HK1199096B - Inkjetsystem for printing a printed circuit board - Google Patents

Description

Ink jet system for printed circuit board

The present invention relates generally to an apparatus, method and use for manufacturing a substrate comprising an ink pattern. In particular, the present invention relates to several aspects of a method and an inkjet system for manufacturing printed circuit boards by printing an ink pattern on a substrate.

A first aspect of the invention relates to a printing method for printing an ink pattern on a substrate based on a usable pattern layout. The substrate is an electronic substrate, in particular a printed circuit board, PCB. The electronic base has a non-conductive substrate and a conductive layer on top of the substrate. A printing process is performed to provide the conductive pattern on top of the electronic substrate. The pattern layout defines a desired layout of an ink pattern to be printed on the upper surface of the substrate. Furthermore, the first aspect of the present invention relates to an inkjet system. In the printing method, an ink pattern is printed on a substrate by an inkjet system to finally generate a conductive pattern. After the ink pattern is printed on the substrate, the substrate is further processed and finally finished by processing stations such as etching and stripping stations. Before selling the substrates, each substrate is independently subjected to a final quality inspection in which the quality of the substrate is checked. Quality inspection means that any defect of the substrate is inspected. The defects may be defects in the printed ink pattern, etch failures, scratches, and the like.

US2007/0154081 discloses a system for inspecting and verifying circuits. The system has a chassis (chassis) including a first station having an Automated Optical Inspection (AOI) apparatus that performs AOI of a circuit to identify defects of candidate objects on the circuit. Further, the backplane comprises a second station having a verification device that performs verification of defects of candidate objects identified by the AOI device. The system includes first and second transportable tables for supporting and transporting first and second circuits, respectively, between first and second stations. After the circuit is fabricated, the substrates are gathered into a batch and transferred to the system for inspection and verification. Each substrate in a batch of substrates is provided to an integrated inspection, verification and correction system in sequence. Integrated inspection means that verification and correction of suspected defects on the inspected substrate is generally performed simultaneously with the inspection of a new substrate. After performing the inspection, verification and correction, additional printed circuit board processing steps, such as applying solder masks, may be performed to finalize the printed circuit board.

Inspection, verification and correction are performed simultaneously to improve productivity. A disadvantage of the disclosed system is that despite this simultaneous operation, the overall production time of each substrate still requires too long time intervals. Inspection and handling of batches of substrates is time consuming and takes up production of printed circuit boards.

It is a general object of the present first aspect of the invention to at least partly obviate the above-mentioned disadvantages and/or to provide a usable alternative. More specifically, it is an object of the first aspect of the invention to provide a method of printing a circuit and a quality inspection which is less time consuming and capable of improving productivity.

According to a first invention of the present invention, this object is achieved by a printing method according to claim 1.

According to a first aspect of the present invention, a printing method for printing an ink pattern onto a substrate is provided. In particular, the substrate is an electronic substrate for electrically connecting electronic devices, more particularly printed circuit boards. The ink pattern to be printed is based on the available pattern layout. The pattern layout defines a desired layout of the ink pattern to be printed.

The printing method according to the first aspect of the present invention comprises the step of providing an ink jet system. The ink jet system includes a frame for housing ink jet system components. The inkjet system includes a printhead assembly for ejecting drops of ink onto a substrate. The printhead assembly is mounted to a frame. The printhead assembly is placed in a printing region of an inkjet system. In the printing process, a printhead assembly is used to print an ink pattern on a substrate. The ink jet system comprises control electronics for controlling the ink jet system. The inkjet system further comprises a scanning unit for scanning the printed ink pattern on the substrate. The scanning unit is mounted to a frame of the inkjet system. Preferably, the scanning unit is positioned adjacent to the printhead assembly to immediately scan the printed ink pattern.

A printing method according to the first aspect of the invention comprises the step of generating an input image for dispensing dot positions of an ink pattern to be printed by a printhead assembly. The input image is based on a pattern layout. Preferably, generating the input image means rasterizing the pattern layout into a raster input image. The raster input image provides an assignment of dot positions of the ink pattern to be printed. The print head assembly is configured to operate and eject ink droplets based on an input image that is input.

A printing method according to the first aspect of the invention comprises the step of providing a substrate to be printed. The substrate may be transported by a substrate conveyor to a printing zone of an inkjet system for printing an ink pattern on an upper surface of the substrate. The upper surface of the substrate may be the front or bottom side of the substrate.

A method of printing according to the first aspect of the invention comprises the step of printing an ink pattern based on an input image onto a substrate by a print head assembly of an inkjet system.

The printing method according to the first aspect of the present invention includes the step of scanning the printed ink pattern by the scanning unit. The scanning unit is arranged to obtain a scanned image, in particular a raster scanned image, of the printed ink pattern.

The printing method according to the first aspect of the present invention comprises the step of comparing the scanned image with the input image to perform a quality check. A quality check is performed to detect any printing defects in the printed ink pattern.

The printing method according to the first aspect of the present invention comprises the step of providing a decision to approve or reject the printed ink pattern on the substrate. In the case of approval, the substrate may be provided to a subsequent processing station to finalize the substrate. The next processing station may be placed adjacent to the ink jet system. In particular, the processing station is an etching station for etching a substrate. In the case of rejection, the substrate including the printing defect may be ejected.

The printing method according to the first aspect of the invention provides quality inspection of the printed substrate, wherein the quality inspection is incorporated in the printing method. Advantageously, the quality check is performed relatively simply by comparing only the scanned image with the input pattern layout. In particular, the scanned image is compared to the input image. Preferably, the scanned image is a raster scanned image which is compared to the raster input image.

Each individual printed substrate can be inspected immediately before further processing steps are carried out. Substrates including printing errors can be directly ejected from the inkjet system. Substrates with printing errors no longer take up the printing process, which increases the productivity of the system. When a printing error is found on the substrate individual, an alarm signal can be generated by the control electronics. The alarm signal may indicate the relevant cause of the printing error. Maintenance may be performed to prevent similar printing errors on subsequent substrates. Thus, embedded quality checks may prevent a series of substrates all including printing errors starting from the same source (e.g., a disturbed nozzle).

The quality check is performed in-line and is controlled by the control electronics of the inkjet system. Embedding means that the quality check is performed after printing the ink pattern on the substrate and before etching the substrate. The quality check may be performed during the step of the first substrate being subjected to printing of the ink pattern on a subsequent substrate. The quality check is preferably performed on the inkjet system. The quality check is preferably performed on a board of the ink jet system, which means that the quality check is performed for a substrate located on the ink jet system. No additional separate inspection system, such as an AIO device, is required. The control electronics and scanning unit of the ink jet system itself are used to perform the quality check.

The quality check is an intermediate quality check performed after printing the ink pattern onto the substrate and before further finishing methods such as etching or peeling of the substrate occur. This intermediate quality check may be performed between two printing steps on the same surface of the substrate. This intermediate quality check may be followed by a final quality check after the manufacture of the substrate is completed. The quality check is performed in an intermediate state of the substrate. Advantageously, the final quality check after etching the substrate may be less extensive. The typical defects of the substrate have been inspected during an intermediate quality inspection at an intermediate stage of the manufacturing process, which allows a more rapid final quality inspection at the end of the manufacturing process.

Intermediate quality checks on the plates of the inkjet system enable several advantageous embodiments.

In an embodiment of the printing method according to the first aspect of the invention, the scanned image is a raster-scanned image which is compared with an input image as a raster input image. The raster input image is generated by rasterizing the pattern layout into a raster input image that is used to assign dot locations of an ink pattern to be printed by the printhead assembly. Advantageously, by comparing only the raster scan image and the raster input image, a quality check can be performed relatively quickly. Rapid quality inspection reduces the support of the substrate and improves the productivity of the inkjet system.

In an embodiment of the printing method according to the first aspect of the invention, the substrate is discharged to a discharge station in case the substrate is rejected. The discharge station may be a waste station for buffering rejected substrates. Each individual substrate is subjected to an embedded quality check before the substrate is finally completed by the etching process. Rejected substrates including printing errors can be separated from the main production stream of substrates being transported through the inkjet system and can be discharged from the main production stream. The rejected substrate will not be transferred to final stations such as etch baths and stripping stations. Early discharge of the rejected substrate no longer reduces the efficiency of the final finished process after the printing process. Advantageously, the finalizing station may only be used to finalize a substrate that has been checked for printing errors. Only approved substrates can be further processed, which provides high efficiency and yield of the manufacturing process for electronic substrates. Substrates that include printing errors will not adversely affect the operational capabilities of further finishing processes.

In addition, a rejected printed substrate does not survive the final inspection of an automated optical inspection AOI unit with a normal length of working time. Thereby, the overall printing process and manufacturing of the electronic substrate may be performed more efficiently. The productivity is improved.

In an embodiment of the printing method according to the first aspect of the invention, the discharge station is a recycle station for recycling (recycle) substrates. After quality inspection is performed on the board of the inkjet system, the rejected substrates are discharged to a recycle station. In the recycle station, the rejected substrate is cleaned by removing the printed ink pattern. The cleaned substrate can then be reused again in the inkjet system. The cleaned substrate may be returned to an input station for inputting the substrate into an inkjet system. Advantageously, process quality inspection, such as etching, after printing the ink pattern and before the final completion of the process allows for recycling of the printed substrate. Recycling the substrate after etching would not be possible in this easy way.

In an embodiment of the printing method according to the first aspect of the invention, the quality check is performed on the substrate in a buffer unit of the inkjet system. The buffer unit is connected to a frame of the inkjet system. The substrate is transported to a buffer unit of the inkjet system. Quality inspection of the substrate is performed in the buffer unit. Preferably, the buffer unit is placed adjacent to the scanning unit of the inkjet system. During the comparison of the scanned image with the input image by the quality inspection, the substrate is temporarily stored in the buffer unit. Upstream substrates in the substrate stream passing through the inkjet system may be printed during quality inspection of downstream placed substrates in the buffer unit.

In an embodiment of the printing method according to the first aspect of the invention, the quality-verifying step is performed on the first substrate while performing the printing step of printing the ink pattern onto the second substrate in the production stream of substrates. The first substrate is placed downstream of the second substrate in a flow of substrates through the inkjet system. The first substrate is subjected to a quality check while the second substrate is printed. The first substrate is placed outside the print area, wherein the second substrate is placed inside the print area. The first substrate is transported to a separate location remote from the print zone to perform a quality check. A separate location may be located in the buffer unit to temporarily store the at least one substrate. By performing a quality check on the substrate in the buffer unit, the quality check does not support the production flow of the substrate. Advantageously, a higher efficiency of the printing method performed by the inkjet system can be achieved.

In particular, the buffer unit may be a rotation buffer unit including a rotation unit for rotating the substrate. In a first step, a substrate may be received in a rotating buffer unit in which an ink pattern is printed on a top side of the substrate. Subsequently, a first quality check may be performed to check the printed ink pattern of the top side. After approval, the first substrate may be turned around by rotating the buffer unit and re-provided in a subsequent step in the printing area of the inkjet system for a subsequent printing step of providing an ink pattern to the bottom side of the substrate. After printing the bottom side of the substrate, a second quality check is performed to check for any defects in the ink pattern printed on the bottom side of the substrate. If the first quality inspection of the ink pattern on the top side shows any defects, the substrate can be discharged from the production stream of substrates.

In a specific embodiment, the inkjet system comprises an input unit arranged as a rotational buffer unit. In the first position, the input unit is arranged for inputting a blank substrate to a printing area of the inkjet system. In the second position, the input unit is arranged for receiving, rotating and inputting the topside printed substrate from the printing area of the inkjet system to the printing area of the inkjet system.

In an embodiment of the printing method according to the first aspect of the invention, the printing method comprises a preparatory step of filtering at least one control feature from an input image (in particular a raster input image) before performing the quality check. The control features are filtered by the control electronics of the ink jet system. The control features define candidate defects for the ink pattern. Candidate defects defined by the control features are inspected during quality inspection. The control features may define specific locations and/or geometries of the input image that may be suspected of being a typographical error. The control features may indicate key geometries and/or blobs of the input image. The control features may define a trajectory, pad, or area. The critical spots may be formed, for example, by small gaps between the distinct geometries. The control features may define areas of the ink pattern that have a higher risk of printing faults during the printing process. During the preparation for the quality-checking step, control features of the input image that contribute to a higher risk of typographical errors are identified and marked. During the comparison step of the quality check, the control features are taken into account in the comparison of the input image and the scanned image, in particular the raster-scanned image. By checking only the control characteristics in making the comparison, the quality check can be performed in a short work time. Due to the filtering control feature, it is not necessary to compare the full details of the scanned image. Thereby, the quality check step can be performed in a relatively short period of time of about thirty seconds. The embedding quality check enables a fast and almost continuous printing process.

In an embodiment of the printing method according to the first aspect of the invention, the preparing step of filtering the at least one control feature to define the candidate defect from the input image is performed at least partly during the printing and/or scanning step of the printing method. The preparatory step of quality checking may be performed at least partially while other steps of the printing method are being performed. The preparatory quality inspection step may be performed over a period of about five minutes. The step of quality inspection may be performed before the printing step of depositing the ink pattern on the substrate is finished. A quality check is performed on the basis of the input image (preferably a raster input image) which is already available before the printing of the ink pattern. Based on the input image, candidate defects may have been identified. The preparatory quality inspection step may be completed at the end of the scanning step of the printing method. The comparison step of the quality check can then be performed directly by comparing the control features of the input image with the scanned image. The intermediate quality checks according to the first aspect of the invention, which are performed at least partially simultaneously in the printing method, can be performed in shorter time intervals compared to the quality checks in separate consecutive steps. Quality checks may be less time consuming. The productivity of the substrate is advantageously increased.

In an embodiment of the printing method according to the first aspect of the invention, the control feature may be of a specific type. The type of control feature may be, for example, an arcuate portion or a chamfered corner portion of the ink pattern to be printed. The control feature may be the location of a connection between two typically distinguishable geometries of the ink pattern. The control feature may indicate, for example, the position of such an input image in which a linear portion is connected to an arc portion. Such connected portions of the ink pattern may provide a higher risk of printing errors. This may result in a poor electrical connection if the connection portion does not provide a reliable bond. Advantageously, by categorizing the control features, quality checks can be performed to minimize the risk of printing errors.

In an embodiment of the printing method according to the first aspect of the invention, each control feature may be grouped in a corresponding group. The first set of control features may be defined, for example, by an annular portion of the ink pattern or a shim. The second set of control features may define line elements of the shape signal trace. The third set may define a hole that forms an electrical connection in the middle of the layered multi-layer substrate. The fourth set of control features may define key blobs, such as gaps (gaps), of the ink pattern. Advantageously, a quality check can be performed on the independent set of control features. Thereby, the quality check may be flexible. The accuracy of the quality check and the working time may be affected by the operator of the printing method by selecting a set of one or more control features to be checked.

In an embodiment of the printing method according to the first aspect of the invention, the control features are selected by applying a mask to the input image, in particular to the raster input image. The mask is arranged to filter out a control feature from the input image. A mask may be applied to mask incoherent regions of the input image to filter out a control feature from the input image. The mask can be preprogrammed in the control electronics of the ink jet system. Advantageously, the selection of the control features by the mask provides a simple way of subtracting the relative positions and geometries of the ink pattern to be inspected during quality inspection.

In an embodiment of the printing method according to the first aspect of the invention, the filtering of the control features comprises at least one selection criterion for filtering at least one critical portion of the input image. The selection criteria make the filtering of the control features dependent on the production environment. The selection criteria define in which circumstances the control feature is selected. The selection criteria may comprise input parameters that may be adjusted by an operator of the inkjet system. The selection criteria may be turned on or off, for example, to consider or not consider critical portions of the ink pattern, respectively. Preferably, the selection criteria are automatically controlled by the control electronics. The selection criteria may be associated with the printing mode and may relate to a desired accuracy or a required printing speed. Other print characteristics may also define criteria. The selection criteria may be print job dependent. Advantageously, by selectively defining the selection criteria, the extraction of control features and quality checks can be performed in a selective and efficient manner.

In an embodiment of the printing method according to the first aspect of the invention, the step of scanning is performed by a scanning unit of an inkjet system. The scanning unit is connected to a frame of the inkjet system. Preferably, the scanning unit is positioned adjacent to a printhead assembly of the inkjet system. The scanning unit includes at least a portion of a light source for illuminating the ink pattern of the substrate. Further, the scanning unit includes an imaging unit for capturing a raster-scanned image. Preferably, the light source is arranged to provide optimal contrast between the ink pattern printed on the substrate and the background formed by the area of the upper surface of the substrate outside the ink pattern. The light source produces illumination of the ink pattern in a particular light color. Preferably, the light source is monochromatic. The emitted light color of the light source is tuned to the extreme reflectance values of the ink pattern and/or the background surface. In practice, the emitted light color corresponds to the color of the ink drop used or to the color of the substrate's upper surface. In particular, the selected blocking color is blue to achieve the best optical contrast with the upper copper surface of the substrate, with the corresponding illumination being red for maximum absorption of the blocking and maximum reflection at the upper copper surface. Thereby, an optimal contrast can be obtained, which improves the scanning process and allows an improved accuracy of the quality check.

In an embodiment of the printing method according to the first aspect of the invention, the printing method comprises the step of marking the substrate before transporting the approved substrate to a further process station. The substrate may be marked with a unique identifier by a marking station to enable tracking of the substrate during manufacturing and on the market. Approved substrates may be labeled with a sequence number.

In an embodiment of the printing method according to the first aspect of the invention, the printing method is incorporated in a manufacturing process for manufacturing an electronic substrate. The printing method is performed in a first stage of the manufacturing process. In the final stage of the manufacturing process, the printed substrate is etched and peeled off. The quality check is performed at the end of the first stage of the manufacturing process, before the beginning of the last stage.

Further, the first aspect of the invention relates to the use of a printing method for manufacturing an electronic substrate. A first aspect of the invention relates to a manufacturing process for manufacturing printed electronic substrates. The electronic substrate is, for example, a display panel or a printed circuit board. In particular, the present invention relates to a printing method for manufacturing a Printed Circuit Board (PCB).

In an embodiment of the manufacturing process according to the first aspect of the invention, the next process station placed after the inkjet system is an etching station for etching the substrate. The etching station may comprise an etching bath filled with an etching liquid. The substrate may be immersed in an etch bath to remove the top layer (specifically the copper layer) from the substrate. After etching the substrate, the substrate may be further processed to a stripping station to strip away the etch-resistant ink. After the ink pattern of the substrate is removed, the substrate is ready for use. Final quality inspection of the substrate may be performed by automated optical inspection. Advantageously, the final inspection can be focused on typical damage that may occur during etching or stripping of the substrate. Typical damage that may result from the printing step has already been checked in the intermediate embedding quality checking process and can advantageously be taken out of the scope of the check in the last stage. This makes the inspection more efficient and less time consuming.

Further, embodiments are defined in the claims.

Further, the first aspect of the present invention relates to an inkjet system for printing an ink pattern on a substrate. The inkjet system includes a substrate conveyor for conveying and moving the substrate. The inkjet system includes an inkjet print head assembly for ejecting ink drops onto the upper surface of a substrate to print an ink pattern. Further, the inkjet system comprises a scanning unit for scanning the printed ink pattern of the substrate. The ink jet system contains control electronics for controlling the ink jet system. The control electronics are configured to perform a printing method according to the first aspect of the invention.

In an embodiment of the ink jet system according to the first aspect of the invention, the control electronics comprise logic circuitry for performing a quality check by comparing a scanned image, in particular a raster scanned image, generated by the scanning unit with an input image, in particular a raster input image generated by the pattern layout. In particular, the logic circuit is configured to extract control features from the input image for preparing a quality check.

In an embodiment of the ink jet system according to the first aspect of the invention, the logic circuit is embedded in the chip. Preferably, the chip is a field programmable chip (FPGA chip). Logic circuitry embedded in the chip may include image modification to improve linearity, up-sampling to improve resolution, noise filtering, and threshold functionality. Advantageously, the logic in the chip runs faster and more reliable than the logic written in software.

In an embodiment of the inkjet system according to the first aspect of the invention, the inkjet system comprises a buffer unit for temporarily storing the substrate. While printing a subsequent substrate in a printing area of the inkjet system, quality inspection of the substrate is performed on the temporarily stored substrate in the buffer unit. In a first stage of the printing method, the substrate is received in a printing area of an inkjet system and printing is performed on a top side of the substrate. Subsequently, the printed ink pattern is checked by quality checking the printing error in the buffer unit. After performing the quality check and approving the substrate, the substrate may be transported out of the inkjet system to a subsequent process station.

In particular, the buffer unit is a rotation buffer unit for temporarily storing the substrate and revolving the substrate. The rotation buffer unit has a rotation unit for rotating the received substrate. The received substrate may be rotated by the rotating unit. The printing method may comprise the step of rotating the substrate in a rotating buffer unit before re-supplying the substrate to the printing zone of the ink jet system. Thereby, both the top side and the bottom side of the substrate may be printed.

The substrate may be rotated by a rotation buffer unit of the inkjet system. After the first stage of the printing method, which comprises the first printing step and the first quality check, the substrate may be again provided to the printing area of the inkjet system in the second stage of the printing method to print the bottom side of the substrate.

In a specific embodiment, the inkjet system comprises an input unit for inputting the substrate into a printing area of the inkjet system, wherein the input unit is arranged to rotate the buffer unit. In a first stage of the printing method, an input unit is arranged for inputting a blank substrate to a printing area of the inkjet system. The blank substrate has a non-printed top side and a bottom side. In a second stage of the printing method, the input unit is arranged for receiving, rotating and inputting the topside printed substrate from the printing area of the inkjet system to the printing area of the inkjet system.

In an embodiment of the ink jet system according to the first aspect of the invention, the scanning unit comprises a light source for illuminating at least a part of the ink pattern of the substrate. Further, the scanning unit includes an imaging unit for capturing a raster-scanned image. Preferably, the light source is arranged to provide optimal contrast between the ink pattern printed on the substrate and the background formed by the area of the upper surface of the substrate outside the ink pattern. The light source produces illumination of the ink pattern in a particular light color. Preferably, the light source is monochromatic. The emitted light color of the light source is tuned to the extreme reflectance values of the ink pattern and/or the background surface. In practice, the emitted light color corresponds to the color of the ink drop used or to the color of the substrate's upper surface. In particular, the selected blocking color is blue to achieve the best optical contrast with the upper copper surface of the substrate, with the corresponding illumination being red for maximum absorption of the blocking and maximum reflection at the upper copper surface. Thereby, an optimal contrast can be obtained, which improves the scanning process and allows an improved accuracy of the quality check.

In an embodiment of the inkjet system according to the first aspect of the invention, the scanning unit comprises an LED light bar as light source. Advantageously, the LED light bar is adapted to provide illumination of monochromatic light. In addition, the intensity of the illumination is fully adjustable.

Further, the present invention relates to a substrate production line for producing electronic substrates, in particular printed circuit boards. The substrate production line comprises an ink jet system according to the first aspect of the invention and further comprises an etching station for etching the substrate. The substrate production line has a main production flow of substrates, in which the substrates are first printed on an inkjet system and subsequently etched at an etching station. The etching station is positioned downstream of the ink jet system. The main production stream is branched. The main production stream is branched off before the etching station. The main process stream contains a substream upstream of an etching station which extends from the inkjet system to a discharge station for discharging the substrates from the main process stream. The substrate may be discharged through the branch flow after the quality inspection of the printed ink pattern of the substrate is performed.

Further embodiments of the first aspect of the invention are defined by the claims.

A second aspect of the invention will now be explained.

A second aspect of the invention relates to an inkjet system, in particular a drop on demand inkjet system for industrial applications.

Drop-on-demand ink jet systems are well known, and have proven successful over the past few years, particularly in the consumer market for inkjet printers for paper applications. An advantage of the ink jet system over other printing techniques, such as impact printing, is that no direct contact between the ink jet system and the substrate is necessary to provide the desired pattern to the substrate. A part of the achievements in consuming inkjet printers is also that manufacturers find ways to develop small and relatively inexpensive inkjet printers.

Recent developments have been directed to the use of ink jet systems in applications other than traditional paper applications. However, these developments have not been very successful, especially when high accuracy and reliability are required.

Due to its simplicity and rapidity, inkjet systems are considered as promising examples of applications for manufacturing tools:

-providing an etch-resistant mask on a Printed Circuit Board (PCB);

-providing a solder mask for PCB manufacturing;

-providing the solar cell with a mask forming an electrode pattern; or

-manufacturing active or passive circuit elements, display elements, antennas and/or electronic components on a substrate comprising a flexible substrate.

The ink jet system can be used to deposit the desired mask layer or structure in a desired pattern, for example, a pattern corresponding to electronic circuitry on a PCB. Depending on the line width of the electronic circuit desired and the size of the ink drops used, missing or misplaced drops can have a significant impact on the operation of the electronic circuit and, therefore, the PCB. For example, missing ink drops may cause the wires to have an undesirably high local resistance, which may even lead to electromigration. The result may be a malfunctioning PCB.

Due to the small drop size of current inkjet systems (typical drop size is 5-50PL), many drops are required to make a typical pattern. For example, the amount of ink drops applied to a substrate, such as a typical 21x24 inch PCB board, will typically be about 109. When a reasonable yield of, for example, 99% is desired, only one error in 1011 drops is allowed. Such a highly reliable ink jet system has not been realized.

Thus, two major challenges in developing an industrially applicable inkjet system are improving the placement accuracy and reliability of the ink droplets to be able to ensure that each desired ink droplet of the pattern has been truly generated and placed on the substrate.

It is therefore an object of the second aspect of the present invention to provide an inkjet system with improved accuracy and/or improved reliability.

To achieve this object, an ink jet system according to item 1 prefixed with 971 is provided.

The advantage of this inkjet system is that each nozzle is already a spare nozzle, which improves reliability, since in case of a nozzle failure another nozzle can take over the printing job of the failed nozzle. Further, by providing spare nozzles in the form of spare print heads, a fault affecting the entire print head is less likely to affect another print head, thereby further increasing reliability. This is in contrast to the situation where spare nozzles are provided in the same way as the print head.

In one embodiment, each print head contains a row (row) of nozzles, which row is placed non-perpendicular to the printing direction, for example at an angle between 45 and 65 degrees with respect to the printing direction. Due to this orientation of the nozzles, the nozzles do not have to be placed very close to each other in order to obtain sufficient resolution in the direction perpendicular to the printing direction. The nozzles are then placed at relatively small distances from each other in a direction perpendicular to the printing direction and at relatively large distances from each other in the printing direction. As a result, the overall distance between nozzles is large enough to prevent, or at least minimize, cross-talk between adjacent nozzles. The advantage is that the required resolution can be obtained by a single print head, and not by combining multiple print heads, which have to be properly aligned to each other after combination.

In an alternative embodiment, the spacing between the nozzles in the horizontal direction perpendicular to the printing direction is not sufficient to obtain the required resolution in a single pass of the substrate, but the resolution is obtained by making multiple passes, i.e. using multiple rows (swing), where the substrate is placed differently each time in said direction perpendicular to the printing direction. While such embodiments may require multiple rows depending on the pattern to be printed, an advantage is that fewer nozzles and/or fewer printheads are required.

In one embodiment, each primary print head (primary print head) has an associated tertiary print head (tertiary print head) arranged at a distance from the primary and secondary print heads (secondary print heads) in the printing direction, wherein each nozzle of the primary print head has a corresponding nozzle at the associated tertiary print head, and wherein the primary print head and its associated tertiary print head are arranged relative to each other such that the virtual printed lines of the corresponding nozzles are located substantially at the same position. This further increases the reliability, since each nozzle now has two redundant nozzles, which can take over the printing operation in the event of a failure. The three redundant nozzles also allow one nozzle to be unusable, for example for either measurement or analysis reasons or for repair reasons, while the other two nozzles can continue printing without any loss of reliability, since one of the two nozzles can still take over printing of the other of the two nozzles.

In one embodiment, the print head assembly comprises a print head holder for holding a plurality of print heads. The print head holder is preferably supported in three different places, for example by a frame, so that the print head holder is stably and statically firmly supported, which improves the positional accuracy of the print head and thus the accuracy of the placement of ink drops by the print head.

In one embodiment, the print head support is held stationary and the substrate holder is allowed to move relative to the print head support. As a result, no disturbances are introduced into the print head holder due to the movement and actuation of the print head holder, which allows the print heads to be accurately positioned relative to each other. In addition, maintenance may be easier once accurate positioning is established, as dynamic variations are not possible.

In one embodiment, the dimension of the printing plane in a direction perpendicular to the printing direction is at least as large as the maximum substrate dimension allowed in said direction to be held by the substrate holder. As a result, less substrate movement is required to complete the printed pattern, which improves the achievable accuracy compared to the case where the size of the printing plane is small.

It is well known from prior art inkjet systems that in the case of a plurality of print heads, aligning the print heads relative to each other is a challenge, especially when thermal effects such as thermal expansion of the print head support are also to be taken into account.

In one embodiment each print head has an associated print head positioning device arranged between said print head and the print head holder for positioning said print heads relative to the print head holder, thereby allowing alignment of the primary print heads to their associated secondary print heads for alignment of the virtual print lines of the corresponding nozzles and for alignment of the primary print heads to each other. In case there are also third level print heads or even more print heads in relation to the primary print heads, they will be aligned properly.

An advantage of providing the print head positioning apparatus separately from the print head support may be that the print head support may be assembled less accurately and can be optimized from a mechanical (strength and stiffness) and thermal (stability) point of view without having to worry about positioning of the print head. Inaccuracies in the print head support can be compensated for by the print head positioning device.

Preferably, each print head positioning device comprises a base member removably mounted on a print head support, and a body connected to the base member for supporting a print head, the body being movable relative to the base member by at least one actuator in a plane substantially parallel to the printing plane. The detachability of the base member has the advantage that the print heads comprising the print head positioning device can be combined and introduced into the print head holder as a single unit. In case of a malfunction it is also easy to remove such a unit and replace it with another unit comprising a print head and a print head positioning device.

The actuators positioning the body of the print head positioning device are preferably arranged between the base member and the body to be replaced together with the unit, but may alternatively be arranged between the print head holder and the body. As a result, the actuators do not have to be replaced with the unit, which may be beneficial from an electrical connection point of view, since both power and data can now be supplied to the actuators via the print head holder.

In one embodiment, the body is movable relative to the base member in a translational direction and a rotational direction, wherein the translational direction preferably has a component in a direction perpendicular to the printing direction. When the print head comprises a row of nozzles and the row is not perpendicular to the printing, the direction of translation is preferably perpendicular to the row. These two degrees of freedom enable setting the desired distance (i.e. pitch or resolution) between adjacent nozzles in a direction perpendicular to the printing direction and enable aligning the print head with another print head in said direction, if no other movement is allowed. In other words, the rotational direction can set the resolution, while the translational direction can align the individual print heads in a direction perpendicular to the printing direction.

In one embodiment, the print heads may not be aligned in the print direction at the same time. However, the alignment problem in that direction can be addressed in different ways, for example by measuring the distance between the print heads and adjusting the timing for each nozzle.

In one embodiment, the body is connected to the base via a resilient hinge such that the body is only movable relative to the base member in a plane parallel to the printing plane. The advantage is that this connection does not introduce motion (play), which results in a better accurate positioning of the print head. Further, a hysteresis free positioning of the print head can be obtained. Preferably, the elastic hinge is made of a locally removed material to allow elastic deformation of the remaining material.

Any connection between the print head and the print head holder is preferably facilitated for manufacturing and for disconnection when the unit formed by the print head and the print head positioning device is to be placed into and/or removed from the print head holder. However, this may not be straight due to the movability of the print head relative to the print head support.

To address this, one or more electrical connections between the print heads and the print head holder are formed via the base member of the print head positioning device, i.e. each print head is electrically connected to the print head holder via the base member of the associated print head positioning device. This can easily be achieved in that the base member is always connected to the print head holder more or less in the same way. The connection from the base member to the print head can then be incorporated into the unit and is preferably flexible in order to cope with the movability of the print head.

In addition to electrical connections, the print head may also require connections to pressure supplies. Such pressure may also be provided to each print head from the print head support via a base member of the associated print head positioning apparatus.

Typically, the print head requires two types of pressure supplies. A pressure supply provides a negative pressure to the printhead that can be used to prevent ink liquid from 'falling' (i.e., leaking) out of the nozzles due to gravity. The overpressure supply provides an overpressure to the print head that can be used to purge the nozzles during maintenance by squeezing ink liquid through the nozzles, without having to use actuators that are used to eject ink drops during normal operation.

In one embodiment, the print head support comprises at least one cavity for applying a negative pressure to one or more print heads, said cavity being connected to said print heads via a base member of an associated print head positioning device.

In one embodiment, the print head support comprises at least one cavity for applying an overpressure to one or more print heads, said cavity being connected to said print heads via a base member of an associated print head positioning device.

In a preferred embodiment, the at least one underpressure chamber and/or the at least one overpressure chamber are incorporated into the print head holder.

Using one or more of the above-mentioned features of operating the connection between the print head and the print head holder via the base member of the associated print head positioning device, the print head holder can advantageously be used to support, for example, the pressure supply and the necessary supply of control electronics, which may be provided on a PCB board to be supported by the print head holder.

In one embodiment, the print head support may further comprise a cooling unit to provide cooling to a predetermined portion of the print head support, e.g. the control electronics and/or the print head. For example, the cooling unit may provide cold air between the control electronics and the print head holder and/or between the control electronics and the print head to reduce heat transfer from the print head holder and/or the print head to the control electronics.

In one embodiment, the print head support comprises a composite material, such as carbon fiber reinforced plastic, in order to minimize thermal expansion and improve thermal stability. Further, a composite material may be applied such that the stiffness of the print head support in a plane parallel to the printing plane is sufficiently high to obtain a precise positioning of the print head. Further, the stiffness of the print head holder may be such that the print head holder can stably support the weight of the print head, which may be up to 45 kg in the case of sixty print heads.

In one embodiment, the unit formed by the print head and the print head positioning device contains a visual indicator to indicate the status of the unit, thereby allowing a distinction to be made between at least a properly functioning print head and a improperly functioning unit that requires maintenance or replacement. In that case, the information provided to the visual indicator is preferably generated from a suitable detection system capable of detecting the status of the print head. Maintenance personnel can benefit from such a visual indicator because it can easily see which unit needs to be replaced/serviced.

In order to minimize thermal effects on the positioning of the print head, the print head positioning device preferably has a symmetrical configuration.

In some ink jet systems, heat may be generated. This is the case, for example, when thermal actuators are used to generate ink droplets, for example, when used in commercially available bubble jet printers. Another possibility is that the ink liquid requires a high working temperature, for example in order to obtain a suitable viscosity and/or to become liquid phase, e.g. a hot melt ink.

However, heat may affect the operation of other components and may have a severe impact on the accuracy of the inkjet system. To minimize the effects of heat, one or more of the following measurements may be made.

-each print head comprises drive electronics, wherein the print head and the print head holder are configured such that the drive electronics are arranged on a part of the print head extending outside the print head holder, and wherein the print head holder comprises a thermal shield, preferably in the form of a thermally isolating layer, on a surface of the print head holder facing the drive electronics in order to minimize heat transfer to the drive electronics,

-the print head holder comprises a heat shield, preferably in the form of a heat isolating layer, on the surface of the print head holder facing the substrate in the printing process to minimize heat transfer to the substrate, and

the print head support is configured to have minimal thermal expansion within the temperature operating range of the inkjet system (e.g. 40-120 degrees celsius), for example by using a suitable material (e.g. carbon fibre reinforced plastic).

The above-mentioned measures in order to minimize the influence of heat can be combined with an active cooling section, which provides cold air from the cooling device to the control electronics or the print head, for example.

In order to be able to position the print heads relative to each other, the inkjet system preferably comprises a droplet detection unit configured to detect the position of droplets ejected onto the substrate in a direction perpendicular to the printing direction.

A calibration unit may be provided which adjusts the position of the print heads based on the output of the drop detection units by driving the actuators of the respective print head positioning devices. In other words, the calibration unit drives the respective print head positioning devices to align the plurality of primary print heads with each other and to align the secondary print heads with their associated primary print heads in a direction perpendicular to the printing direction. The driving of the individual print head positioning devices is done in dependence of the output of the drop detection unit.

The sequence of detecting and adjusting the position of the print head may be performed several times until the desired positional accuracy of the ejected ink drops is obtained.

When desired, the droplet detection device may also be configured to detect droplets ejected onto the substrate in the printing direction. The calibration unit is then preferably configured to determine, for each nozzle, timing information that enables the nozzle to eject at precise times in order to obtain individual ink drops that are placed at desired locations on the substrate.

To improve the accuracy of the drop detection unit, the drop detection unit may emit light having a frequency that is readily absorbed by the ink liquid and not absorbed by the substrate (or vice versa), and/or be sensitive to such light. This has the advantage that maximum contrast is obtained.

In one embodiment, the drop detection unit is disposed next to the printhead assembly in the printing direction. The droplet detection unit is preferably a line scanner which scans the surface of the substrate while the substrate is moved (e.g. moved downwards) relative to the droplet detection unit. The scanning may be performed at full pass speed so that a full image of the substrate can be obtained at speed.

In one embodiment, the drop detection unit comprises a plurality of optical units, each of which is capable of scanning a portion of the substrate surface, wherein each of the plurality of optical units has a detection range that at least partially overlaps the detection range of an adjacent optical unit, and wherein the detection ranges are combined electronically or by using software to act as a single optical unit. The optical unit may contain a lens imaging system and a linear CMOS sensor in combination with image capture electronics hardware. The time at which the detection ranges at least partially overlap can be advantageously used to improve the detection accuracy in the overlapping range, since twice as much data is obtained in this overlapping region.

In one embodiment, the drop detection unit is supported by a strong and rigid support member, preferably made of a composite material with high thermal stability (e.g. carbon fibre reinforced plastic).

The drop detection unit preferably has a relatively large depth of focus, for example about 50 microns, in order to enable the thickness or height of the substrate to be varied without having to adjust the drop detection unit or adjust the position of the substrate.

In one embodiment, the drop detection unit can be calibrated by scanning a precise pre-pattern that can be used to combine different optical units to act as a single optical unit in the presence of multiple optical units, but can also be used to compensate for lens distortion in one or more optical units, for example.

In one embodiment, the drop detection unit may also be used to inspect the printed pattern to verify the printing performance for a particular print job, i.e. the obtained pattern is compared to a desired pattern, e.g. to verify the quality of the equipment manufactured by the inkjet system.

The second aspect of the invention also relates to a method for mutually accurate positioning of a plurality of print heads, the method comprising at least the following steps:

-printing a test pattern on a test substrate using all print heads;

-obtaining an image of the printed test substrate by means of a drop detection unit;

-determining a centroid for each printed drop from the obtained image;

-comparing the determined centroid with a desired centroid for each ink drop;

-determining a position adjustment for each print head by comparison; and is

-adjusting the position of the print head based on the position adjustment information.

The method can be repeated as many times as necessary to obtain the desired positional accuracy of the print head.

The test substrate may contain a pre-formed calibration pattern which is first measured by the drop detection unit and which can advantageously be used to calibrate the drop detection unit itself, or can be used as a reference for comparing the printed test pattern with the desired test pattern.

In addition to obtaining information about the position adjustment for each print head, the method can also be used to obtain timing information for the print heads, which is advantageously used to properly time the ejection of the nozzles so as to place the ink drops in the correct locations on the substrate. In this case, the timing determines the location of the ink drops on the substrate in the print direction, and the position of the nozzles (i.e., print head alignment) determines the location of the ink drops on the substrate in a direction perpendicular to the print direction.

The second aspect of the invention further relates to a method for printing a pattern on a substrate using an inkjet system having a primary, a secondary and a tertiary print head as described above, wherein the method comprises the steps of:

-alternately printing with at least one primary print head and its associated secondary print head;

-measuring the print performance of the primary or associated secondary print head at each nozzle of the other (i.e. the primary or associated secondary print head that is not printing) while printing with the primary or associated secondary print head;

-predicting a future printing performance of each nozzle based on the measured printing performance;

-if the predicted future printing performance of a nozzle is not satisfactory, stopping printing with said nozzle and continuing printing with the corresponding nozzle of the third stage print head until the printing performance of said nozzle and the predicted future printing performance have improved to the desired level.

In one embodiment, the method is dependent on the direction in which the substrate is moved relative to the printhead assembly. Because the substrate is movable in the printing direction relative to the print head assembly, both directions of movement are possible, i.e., a positive printing direction is alternatively referred to as a leading line and a negative printing direction is alternatively referred to as a trailing line. The first two print heads through which the substrate passes during a row are preferably printed alternately, and the last print head to pass is preferably used to replace the nozzles of the first two print heads if necessary. This has the advantage that replacement nozzles can always be realized, since the substrate to be printed still has to pass the last print head.

In one embodiment, control electronics are provided to determine which nozzle must eject a drop in order to achieve the desired pattern. From the perspective of the control electronics, the primary print head and its associated secondary and tertiary print heads are preferably considered a print head. The control electronics then send information to the printhead cluster controller about the nozzles that must be printed. The group controller receives information about the printing performance of the nozzles and, if necessary, knows whether forward or backward travel has been performed. Based on this information, the group controller, independent of the other group controllers and control electronics, decides which print head, i.e. which primary, secondary or tertiary print head, is to be used to print the pattern received from the control electronics. In this way the amount of data that has to be transported through the system is reduced compared to the case where the control electronics have to drive all print heads (primary, secondary and tertiary) independently. As a result, switching between nozzles can be performed more quickly.

In one embodiment, when the third stage print head takes over the printing job of at least one nozzle of the primary or secondary print head, it may occur that the primary or secondary print head still printing or the corresponding nozzle of the third stage print head also shows unsatisfactory performance. In this case, the remaining nozzles will be used to continue printing without alternating between the two print heads. Preferably, the method comprises: if at most one nozzle of a corresponding set of nozzles is available for printing as described above, an alarm signal is provided, since the risk of missing ink droplets may become undesirably high.

Based on the alarm signal, printing may be temporarily stopped and/or maintenance may be performed, for example by performing an automatic maintenance procedure using a maintenance unit such as a wiper, or maintenance personnel may be alerted to manually check the system.

The second aspect of the present invention further relates to a method for printing a pattern on a substrate using the ink jet system according to the second aspect of the present invention, wherein the method comprises the steps of:

-measuring the printing performance of the nozzle;

-comparing the measured printing performance of the primary print head corresponding nozzle with its secondary and, if present, tertiary print heads and determining the nozzle with the best printing performance;

printing with the nozzle having the best printing properties.

The method may be performed periodically or even continuously in order to minimize the risk of the printing performance dropping to an undesirable level. It is even possible to periodically temporarily suspend printing in order to be able to carry out the method, whereby printing with the nozzles having the best printing performance can be continued subsequently.

This has the advantage of printing with the best performing nozzles at all times in order to improve accuracy and reliability.

An embodiment according to the second aspect of the invention may be defined by the following 971 as a prefix term:

971 — 1. the ink jet system comprises:

a print head assembly having a plurality of print heads, wherein each print head comprises at least one nozzle which can eject a drop of ink liquid towards a substrate in an ejection direction, and wherein the plurality of print heads together define a printing plane perpendicular to the ejection direction,

a substrate holder for holding a substrate,

wherein the substrate support is movable relative to the print head assembly in a printing direction parallel to the printing plane,

and wherein each nozzle has a virtual printed line on the substrate on which droplets of ink liquid can be deposited as the substrate is moved relative to the printhead assembly in only the printing direction,

it is characterized in that

The plurality of print heads comprises at least one primary print head, each primary print head having an associated secondary print head arranged at a distance from the primary print head in the printing direction, wherein each nozzle of the primary print head has a corresponding nozzle on the associated secondary print head, and wherein the primary print head and its associated secondary print head are arranged relative to each other such that the virtual printed lines of the corresponding nozzles are located substantially at the same position.

971_2 an ink jet system according to clause 971_1, wherein each print head comprises a row of nozzles, said row being positioned not perpendicular to the printing direction, preferably at an angle of 45 degrees with respect to the printing direction.

971_3. an ink jet system according to clauses 971_1 or 971_2, wherein each primary print head has an associated tertiary print head arranged at a distance from the primary and secondary print heads in the printing direction, wherein each nozzle of the primary print head has a corresponding nozzle on the associated tertiary print head, and wherein the primary print head and its associated tertiary print head are arranged relative to each other such that the virtual printed lines of the corresponding nozzles are located substantially at the same position.

971_4. an inkjet system according to the previous 971_ version, wherein the printhead assembly comprises a printhead support for supporting a plurality of printheads.

971_5 an inkjet system according to clause 971_4, wherein the print head holder is supported only at three different locations.

971_6 inkjet system according to one or more of the previous 971_ clauses, wherein the printhead assembly is kept stable and the substrate holder is movable.

971_7. the ink jet system according to item 971_6, wherein in a direction perpendicular to a printing direction, a dimension of the printing plane is at least as large as a maximum dimension allowed in said direction that can be held by the substrate holder.

971_8 an ink jet system according to clause 971_4, wherein each print head has an associated print head positioning device arranged between said print head and print head holder for positioning said print head relative to the print head holder, so as to be able to align the primary print heads with their associated secondary print heads, thereby causing the virtual print lines of the corresponding nozzles to be located at the same position.

971_9 an ink jet system according to clause 971_8, wherein each print head positioning device comprises a base member removably mounted to a print head support and, connected thereto, supports a body of a print head, wherein the body is movable relative to the base member by an actuator in a plane substantially parallel to the printing plane.

971_10 the ink jet system according to item 971_9, wherein the main body is movable relative to the base member in a translational direction and a rotational direction.

971_11 inkjet systems according to clauses 971_2 and 971_10, wherein the direction of translation is perpendicular to the direction in which the rows extend.

971_12 an ink jet system according to item 971_9, wherein the main body is connected to the base member via a resilient hinge, whereby the main body is movable relative to the base member only in said plane parallel to the printing plane.

971_13 an inkjet system according to clause 971_9, wherein each print head is electrically connected to the print head holder via a base member of an associated print head positioning device.

971_14. an ink jet system according to clause 971_9, wherein pressure is provided to each print head from the print head holder via a base member of the associated print head positioning device.

971_15 an inkjet system according to clause 971_14, wherein the print head holder comprises a chamber for applying a negative pressure to one or more print heads, said chamber being connected to said print heads via a base member of an associated print head positioning device.

971_16 an inkjet system according to clause 971_14, wherein the print head holder comprises a chamber for applying an overpressure to one or more print heads, said chamber being connected to said print heads via a base member of an associated print head positioning device.

971_17 inkjet system according to one or more of the previous 971_ clauses, wherein the print head holder comprises a cooling unit providing cooling to the print head holder and/or a predetermined portion of the print head.

971_18 an ink jet system according to clause 971_8, wherein the unit formed by the print head and the print head positioning device contains a visual indicator indicating the status of the unit, thereby allowing a distinction to be made between at least a normally operating print head and a malfunctioning unit that needs to be replaced.

971_19 an inkjet system according to clause 971_8, wherein the print head positioning device has a symmetrical configuration to minimize thermal variations.

971_20 an inkjet system according to clause 971_4, wherein each print head comprises drive electronics, wherein the print head and the print head holder are configured such that the drive electronics are arranged on a portion of the print head extending from the print head holder, and wherein the print head holder comprises a thermal shield, preferably in the form of a thermal isolation layer, on a surface facing the drive electronics in order to minimize heat transfer to the drive electronics.

971_21 an inkjet system according to clause 971_4, wherein the print head holder comprises a thermal shield, preferably in the form of a thermal isolation layer, on a surface facing the substrate in the printing process, to minimize heat transfer to the substrate.

971_22 an inkjet system according to clause 971_4, wherein the print head support comprises a composite material, such as carbon fiber reinforced plastic, in order to minimize thermal expansion.

971_23. the ink jet system according to item 971_8, wherein a droplet detecting device is provided to detect a position of a droplet ejected on the substrate in a direction perpendicular to a printing direction.

971_24. the ink jet system according to clause 971_23, wherein a calibration unit is provided which drives the respective print head positioning devices based on the output of the droplet detection devices so as to align the primary print heads with each other and to align the secondary print heads with their associated primary print heads.

971_25. the ink jet system according to clause 971_23, wherein the droplet detecting device is further configured to detect a position of a droplet ejected onto the substrate in the printing direction.

971_26 the ink jet system according to clauses 971_24 and 971_25, wherein the calibration unit is configured to determine, for each nozzle, timing information capable of accurately timing the ejection of the nozzle so as to obtain an ink droplet ejected from the nozzle at a desired location.

971_27. the ink jet system according to clause 971_23, wherein the ink droplet detecting device emits and detects light at a frequency that is readily absorbed by the ink liquid and not absorbed by the substrate.

971_28 the ink jet system according to item 971_23, wherein the droplet detection unit is disposed close to the head assembly in the printing direction.

971_29. the ink jet system according to clause 971_23, wherein the droplet detection unit is a line scanner that scans the surface of the substrate while the substrate moves relative to the droplet detection unit.

971_30. the ink jet system according to clause 971_23, wherein the ink droplet detecting unit comprises a plurality of optical units each capable of scanning a portion of the surface of the substrate, wherein each of the plurality of optical units has a detection range at least partially overlapping a detection range of an adjacent optical unit, and wherein the detection ranges are combined electronically or by using software to act as a single optical unit.

971_31. the ink jet system according to item 971_23, wherein the ink droplet detecting unit is supported by a strong and rigid support member preferably made of a composite material having high thermal stability, such as carbon fiber reinforced plastic.

971 — 32. a method for mutually accurate positioning of a print head, the method comprising at least the steps of:

-printing on a test substrate using all print heads;

-obtaining an image of the printed test substrate by means of a drop detection unit;

-determining a centroid for each printed drop from the obtained image;

-comparing the determined centroid with a desired centroid;

-determining a position adjustment for each print head based on the comparison; and is

-adjusting the position of the print head relative to the print head support based on the position adjustment information.

971_33. a printing method for printing a pattern on a substrate, wherein an ink jet system according to item 971_3 is used, characterized in that the method comprises the steps of:

-alternately printing with at least one primary print head and its associated secondary print head;

-measuring the print performance of each nozzle of the other of the primary or related secondary print heads, i.e. the primary or related secondary print head that is not printing, while printing with the primary or related secondary print head;

-predicting a future printing performance of each nozzle based on the measured printing performance;

-in case the predicted future printing performance of a nozzle is not satisfactory, stopping printing with said nozzle and continuing printing with the corresponding nozzle of the third stage print head until the printing performance of said nozzle and the predicted future printing performance have improved to the desired level.

971_34. a printing method for printing a pattern on a substrate, wherein an ink jet system according to item 971_1 is used, characterized in that the method comprises the steps of:

-measuring the printing performance of the corresponding nozzles of the primary print head and its secondary print head, and, if a tertiary print head is present, of the corresponding nozzles of the tertiary print head;

-comparing the printing performance of the corresponding nozzles and determining the nozzle with the best printing performance;

printing with the nozzle having the best printing properties.

A third aspect of the invention will now be explained.

A third aspect of the present invention is directed to a hot melt ink metering system. Hot melt inks are materials that can be ejected from an inkjet system. Because the inherent property of hot melt inks is that they are solid at normal room temperature, they need to be heated to an elevated temperature to melt so that they can be jetted by an ink jet system toward a substrate, after which the ink can solidify on the substrate to form the desired pattern on the substrate.

Hot melt inks present some challenges in supplying hot melt inks to inkjet system printheads compared to aqueous inks. One of the challenges is to do this in a reliable manner so that at any time during the printing operation of the inkjet system, there is sufficient hot melt ink properly prepared for ejection by the print head, i.e. sufficient hot melt ink having a suitable predetermined operating temperature.

Another challenge may be that while doing so, the hot melt ink may age due to the thermal load applied to obtain and maintain a predetermined operating temperature of the hot melt ink, which means an undesirable change in the properties of the hot melt ink. Aging is especially a problem when increasing the number of print heads, as this typically results in large size reservoirs and thus in holding large amounts of ink at high temperatures for longer periods of time. From the reservoir, the hot-melt ink is then supplied to the respective print head via a corresponding supply line.

Another disadvantage of having a large reservoir is that during start-up of the system, it takes a relatively long time for the system to heat up a corresponding large amount of hot melt ink.

It is therefore an object of a third aspect of the present invention to provide a hot melt ink metering system in which the risk of ageing of the hot melt ink is reduced whilst ensuring that the hot melt ink is available at a predetermined operating temperature when required.

The object of the present invention is achieved by providing a hot melt ink metering system according to clause 972_1.

The circulation of hot melt ink across the fluidic connections in a closed circuit has the advantage that the size of the required reservoir is substantially independent of the number of print heads connected to the hot melt ink metering system, while at the same time the predetermined operating temperature of the circulating hot melt ink can be easily maintained for reliability purposes, relative to prior art hot melt ink systems where the hot melt ink is substantially steady state. What needs to be adjusted to the number and size of the print heads is the length of the fluid lines and the number of fluid connections that close the circuit. The reservoirs may then be sized for the estimated consumption rate and perhaps the desired refill rate for each printhead to minimize the amount of molten hot melt ink in the metering system.

In one embodiment, the reservoir may be connected to a hot melt ink tank containing a predetermined amount of solid hot melt ink to replenish the closed circuit. The heating system preferably includes a separate heating element to provide heat to the fusible ink tank when connected to the reservoir so that the fusible ink can be melted and provided to the reservoir in the liquid phase. A control system may be provided which controls the heating element in accordance with the amount of hot melt ink circulating in the closed circuit. The control system may be configured to replenish the closed circuit with melted hot melt ink when the amount of hot melt ink in the closed circuit falls below a predetermined minimum value, such that the hot melt ink is subjected to a thermal load only in the event of a consumption requirement of the inkjet system. This further reduces the chance of the hot melt ink changing properties due to aging, since the amount of hot melt ink in the liquid phase in the metering system is relatively low and therefore the average residence time in the hot melt ink metering system is low.

The relatively small amount of liquid hot melt ink in the metering system has the advantage of reducing the start-up time of the system, during which time the hot melt ink in the closed circuit must be melted.

To measure the amount of hot melt ink in the closed circuit, the metering system may include a level sensor to measure the level of hot melt ink in the reservoir. The output of the level sensor is then provided to a control system which in turn drives the heating system dependent thereon.

In one embodiment, the level sensor is configured to detect whether a level of hot melt ink in the reservoir exceeds or is below a predetermined minimum level, wherein the level sensor comprises a tubular metering tank having a bottom open end disposed at a height in the reservoir corresponding to the predetermined minimum level, an air volume displacing device connected to the metering tank to supply a predetermined volume of air to the metering tank, and a pressure sensor to measure an air pressure differential between an air pressure in the metering tank and an air pressure in the reservoir above the hot melt ink.

Supplying a predetermined volume of air to the metering tank with the air volume displacement device will result in a pressure differential between the air pressure in the metering tank and the air pressure in the reservoir above the hot melt ink if the level of hot melt ink in the reservoir is above the minimum liquid level, and will not result in a pressure differential between the air pressure in the metering tank and the air pressure in the reservoir above the hot melt ink if the level of hot melt ink in the reservoir is below the minimum liquid level. Thus, periodically supplying a predetermined volume of air to the metering tank and measuring the pressure differential provides information about the level of hot melt ink in the reservoir being below or above a predetermined minimum level, based on which information it may be decided to replenish the hot melt ink with the control system.

In one embodiment, a predetermined amount of hot melt ink may be automatically provided to the reservoir from the hot melt ink tank when the level of the hot melt ink falls below a predetermined minimum level. In that case, it is preferable that the amount of the hot-melt ink in the cartridge corresponds to a predetermined amount. Alternatively, however, the heating system may be operated to melt the hot melt ink in the cartridge until the level of liquid in the reservoir has risen to a predetermined maximum level. To achieve this, a level sensor similar to that described above may be used for the lowest level, such that the level sensor is configured to detect whether the level of hot melt ink in the reservoir exceeds or falls below a predetermined highest level, wherein the level sensor comprises a tubular metering tank having a bottom open end disposed at a height in the reservoir equivalent to the predetermined highest level, an air volume displacing device connected to the metering tank to supply a predetermined volume of air to the metering tank, and a pressure sensor that measures the air pressure differential between the air pressure in the metering tank and the air pressure in the reservoir above the hot melt ink.

Because the predetermined operating temperature of hot melt inks is above 100 degrees celsius and/or hot melt inks can sometimes be very aggressive, i.e. have a low pH, the level sensor needs to be able to cope with these conditions. Sensors of the above kind are well suited for use in these environments, since they utilize air pressure in combination with a steady-state component. As a result, the level sensor is reliable due to the lack of moving parts. Further, electrical components such as for pressure sensors and drive electronics for air volume displacement devices may be placed at a safe distance from the reservoir and connected to the metering tank and reservoir via tubes to provide an explosion-and spark-free level sensor. The volume of the tube is preferably smaller than the volume of the metering slot.

Another advantage of the level sensor may be that the level sensor is not dependent on the hot melt ink material and/or temperature.

Elements that can be connected to the hot melt ink, such as the metering slot, can be made of a suitable material that is inserted into the hot melt ink, for example, that can withstand corrosion.

In one embodiment, the reservoir has a surface area-to-volume ratio of 50[1/m ], preferably at least 100[1/m ] and most preferably at least 150[1/m ]. This is advantageous because the heating system is typically configured to apply heat to the reservoir via the outer surface of the reservoir such that the larger the surface area-to-volume ratio of the reservoir, the faster the volume inside the reservoir is heated by the outer surface. Since a large surface area-to-volume ratio typically results in one of the dimensions becoming quite large, the reservoir may be folded to give a U-shaped cross-section, thereby keeping the overall size of the reservoir within predetermined values. Preferably, the reservoir is arranged inside the reservoir with a maximum distance of at most 10mm, preferably at most 5mm, from the closest wall of the reservoir.

The hot melt ink cartridge is preferably a replaceable unit that is replaced with a full cartridge after it becomes empty. The reservoir may be configured to be connectable to more than one cartridge at the same time, so that, for example, a cartridge may be filled into the reservoir each time the liquid level in the reservoir drops below a predetermined minimum level, without requiring immediate manual replacement of the cartridge. And then only after the last cassette is empty needs manual replacement.

In one embodiment, the hot melt ink cartridge has a bottom opening in fluid communication with the reservoir when connected to the reservoir so that the molten hot melt ink will automatically flow to the reservoir due to gravity. Preferably, a spacer is placed inside the hot melt ink tank at a distance above the opening between the solid hot melt ink and the opening, wherein the spacer has a surface area at least as large as the opening, and wherein the spacer is arranged inside the hot melt ink tank such that the molten hot melt ink has to flow around the spacer towards the opening. As a result, a vacuum is prevented from being generated in the cartridge, which would prevent the hot-melt ink from flowing out of the cartridge. Thus, emptying of the cartridge may be ensured, which makes the metering system more reliable when used in an inkjet system.

In one embodiment, the spacer is a plate with a plurality of ridges (ridges) that automatically provide the desired distance between the plate and the bottom of the hot melt ink tank.

In one embodiment, the spacer is a plate with extended raised branches to provide a desired distance between the plate and the side walls of the hot melt ink tank.

In one embodiment, the hot melt ink tank may be connected to a connecting element of the reservoir, wherein the connecting element comprises a siphon tube to provide gas separation between air inside the reservoir and air outside the reservoir. Even without a cartridge connected to the reservoir, smoke or gas cannot escape from the reservoir through the connecting element due to the relatively high temperature inside the reservoir, thereby preventing a dangerous situation for other elements or persons working in the vicinity of the metering system.

In one embodiment, the metering valve is operated by air pressure, which provides the same advantages as a level sensor, since the actuation of the metering valve is explosion and spark free due to the use of air pressure.

The third aspect of the present invention also relates to a method for metering hot melt ink to a plurality of print heads of an inkjet system, the method comprising the steps of:

-heating a portion of the hot melt ink to a predetermined working temperature to allow the hot melt ink to flow;

-circulating heated hot melt ink in a closed circuit;

tapping heated hot melt ink from the closing circuit to the print head if required.

In one embodiment, the method further comprises the step of replenishing the hot melt ink in the event that the amount of hot melt ink in the closed circuit falls below a predetermined minimum value. Preferably, refilling is stopped when the quantity of hot melt ink in the closed circuit reaches a predetermined maximum value.

A third aspect of the present invention also relates to a level sensor for detecting whether a level of hot-melt ink in a container is higher or lower than a predetermined level, wherein the level sensor comprises a tubular metering tank having a bottom open end disposed in the reservoir at a height corresponding to the predetermined level, an air volume displacing device connected to the metering tank for supplying a predetermined volume of air to the metering tank, and a pressure sensor for measuring an air pressure difference between an air pressure in the metering tank and an air pressure in the container above the hot-melt ink.

The third aspect of the invention further relates to a hot melt ink tank for an ink jet system, comprising an opening, wherein a spacer is placed inside the hot melt ink tank at a distance from the opening between the solid hot melt ink and the opening, wherein the spacer has a surface area at least as large as the opening, and wherein the spacer is arranged inside the hot melt ink tank such that the molten hot melt ink has to flow around the spacer towards the opening to leave the hot melt ink tank.

The third aspect of the present invention further relates to an ink jet system, in particular a drop on demand ink jet system comprising a hot melt ink metering system according to the present invention.

It is envisaged that the different aspects of the invention may be combined with each other.

An embodiment according to the third aspect of the invention may be defined by prefixing 972:

972_1. a hot melt ink metering system for metering hot melt ink to a plurality of printheads of an inkjet system, comprising:

-a closed circuit comprising a fluid line, a reservoir, a pump and a heating system, wherein the reservoir is arranged in the fluid line and is configured to contain hot melt ink, wherein the pump is arranged in the fluid line and is configured to circulate (circulate) the hot melt ink in the closed circuit, and wherein the heating system is configured to heat the hot melt ink in the closed circuit to a predetermined operating temperature allowing the hot melt ink to flow in the closed circuit;

-one fluid connection per print head, said fluid connections being connected to fluid lines of a closed circuit, wherein each fluid connection comprises a metering valve to meter the amount of hot melt ink provided to the respective print head.

972_2. a hot melt ink metering system according to clause 972_1, wherein a reservoir is connectable to a hot melt ink cartridge containing a quantity of hot melt ink to replenish a closed circuit with hot melt ink.

972_3. a hot melt ink metering system according to 972_2, wherein the heating system comprises a heating element capable of supplying heat to the hot melt ink tank with the reservoir connected to the hot melt ink tank.

972_4. a hot melt ink metering system according to clause 972_1, including a level sensor to detect a level of hot melt ink within the reservoir.

972_5. the hot melt ink metering system according to clause 972_4, wherein the level sensor is configured to detect whether a level of the hot melt ink in the reservoir exceeds or falls below a predetermined minimum level, wherein the level sensor comprises a tubular metering slot having an open end disposed at a height in the reservoir equivalent to the predetermined minimum level, an air volume displacing device connected to the metering slot to supply a predetermined volume of air to the metering slot, and a pressure sensor that measures an air pressure differential between an air pressure in the metering slot and an air pressure in the reservoir above the hot melt ink.

972_6. a hot melt ink metering system according to clause 972_4, wherein the level sensor is configured to detect whether a level of the hot melt ink in the reservoir is above or below a predetermined maximum level, wherein the level sensor comprises a tubular metering tank having an open end disposed at a height in the reservoir equivalent to the predetermined maximum level, an air volume displacing device connected to the metering tank to supply a predetermined volume of air to the metering tank, and a pressure sensor that measures an air pressure differential between an air pressure in the metering tank and an air pressure in the reservoir above the hot melt ink.

972_7. a hot melt ink metering system according to clause 972_1, wherein the reservoir has a surface area to volume ratio of at least 50[1/m ], preferably at least 100[1/m ] and most preferably at least 150[1/m ].

972_8. a hot melt ink metering system according to clause 972_7, wherein the reservoir has a U-shaped cross-section.

972_9. a hot melt ink metering system according to clause 972_7, wherein the reservoir is configured such that inside the reservoir, the maximum distance from the closest wall of the reservoir is at most 10mm, preferably at most 5 mm.

972_10. a hot melt ink metering system according to clause 972_2, comprising at least one hot melt ink cartridge.

972_11. a hot melt ink metering system according to clause 972_10, wherein when the hot melt cartridge is connected to a reservoir, the hot melt ink cartridge comprises an opening in a bottom of the hot melt ink cartridge, thereby enabling the molten hot melt ink to flow into the reservoir due to gravity, wherein a spacer is placed inside the hot melt ink cartridge at a distance from the opening between the solid hot melt ink and the opening, wherein the spacer has a surface area at least as large as the opening, and wherein the spacer is arranged inside the hot melt ink cartridge such that the molten hot melt ink must flow around the spacer to the opening.

972_12. a hot melt ink metering system according to clause 972_11, wherein the spacer is a plate with a plurality of ridges that automatically provide a desired distance between the plate and a bottom of the hot melt ink cartridge.

972_13. a hot melt ink metering system according to clause 972_11, wherein the spacer is a plate with a divergent path extending to provide a desired distance between the plate and a sidewall of the hot melt ink tank.

972_14. a hot melt ink metering system according to clause 972_2, wherein the hot melt ink cartridge is connectable to a connecting member of the reservoir, and wherein the connecting member comprises a siphon tube to provide a gas separation between air inside the reservoir and air outside the reservoir.

972_15. a hot melt ink metering system according to clause 972_1, wherein the metering valve is operated by air pressure.

972_16. a method for metering hot melt ink to a plurality of print heads of an inkjet system, the method comprising the steps of:

-heating a portion of the hot melt ink to a predetermined working temperature to enable the flow of the hot melt ink;

-circulating heated hot melt ink in a closed circuit;

tapping heated hot melt ink from the closing circuit to the print head if required.

972_17. the method of clause 972_16, further comprising the step of replenishing the hot melt ink in the event that the amount of hot melt ink in the closed circuit falls below a predetermined minimum.

972_18. method according to clause 972_17, wherein refilling is stopped when the quantity of hot melt ink in the closed circuit reaches a predetermined maximum value.

A fourth aspect of the invention will now be explained.

A fourth aspect of the invention relates to an inkjet system, in particular a drop on demand inkjet system for industrial applications.

Drop-on-demand ink jet systems are well known, and have proven successful over the past few years, particularly in the consumer market for inkjet printers for paper applications. An advantage of the ink jet system over other printing techniques, such as impact printing, is that no direct contact between the ink jet system and the substrate is necessary to provide the desired pattern to the substrate. A part of the effort in consuming inkjet printers is also that manufacturers have found ways to develop small and relatively inexpensive inkjet printers.

Recent developments have been directed to the use of ink jet systems in applications other than traditional paper applications. However, these developments have not been very successful, especially when high accuracy and reliability are required.

Examples of applications for which inkjet systems are considered promising manufacturing tools due to their simplicity and rapidity are:

-providing an etch-resistant mask on a Printed Circuit Board (PCB);

-providing a solder mask for PCB manufacturing;

-providing the solar cell with a mask forming an electrode pattern; or

-manufacturing active or passive circuit elements, display elements, antennas and/or electronic components on a substrate comprising a flexible substrate.

The ink jet system can be used to deposit the desired mask layer or structure in a desired pattern, for example, a pattern corresponding to electronic circuitry on a PCB. Depending on the line width of the electronic circuit desired and the size of the ink drops used, missing or misplaced drops can have a significant impact on the operation of the electronic circuit and, therefore, the PCB. For example, missing ink drops may cause the wires to have an undesirably high local resistance, which may even lead to electromigration.

Inkjet systems typically include a printhead assembly having at least one printhead, which is an integrated unit configured to eject drops of ink fluid from nozzles disposed in a printhead surface toward a substrate. Ink fluid that has accumulated on the printhead surface and that interacts with ink fluid inside the nozzles or with ink drops exiting the nozzles, thereby altering the intended trajectory of the ejected ink drops, can cause mispositioning of the ink drops to occur.

Nozzles that are obstructed by dried or cured ink fluid may cause missing ink drops. This can be addressed by purging the nozzle with an overpressure that forces the ink fluid out of the nozzle, thereby removing the portion of the ink fluid that blocks the nozzle. Disadvantageously, purging may cause ink fluid to accumulate on the surface of the printhead, which in turn may cause misplacement of ink drops.

To prevent the misplacement of ink drops due to ink fluid on the surface of the print head, prior art inkjet systems utilize a maintenance unit having a wiper that is moved relative to the surface of the print head to remove the ink fluid present on the surface by moving the wiper while holding the print head steady, moving the print head while holding the wiper steady, or moving both the wiper and the print head.

A disadvantage of the maintenance units used at present is that the wiping performance is unsatisfactory, for example due to changes in the characteristics of the wiper which may occur as a result of ageing of the wiper. As a result, not all of the ink fluid may be removed from the surface of the printhead during the wiping action, which negatively impacts the achievable accuracy and reliability of the inkjet system and thus limits the number of industrial applications in which the inkjet system may be used.

It is therefore an object of a fourth aspect of the invention to provide a service unit with improved wiping properties, which in turn preferably leads to a more accurate and reliable ink jet system.

According to a first subsidiary aspect of the fourth aspect of the invention, this object is achieved by providing a maintenance unit according to clause 973_1. A first sub-aspect of the fourth aspect of the invention is based on the understanding that: an important parameter of the wiping action is the force, i.e. the wiping force with which the wiper is pressed against the surface of the print head, and the wiping force has to be controlled in order to cope with the changing properties of the wiper. The position control of the prior art wiper cannot be used to reliably control the wiping force, since the wiping force with which the wiper is pressed against the print head surface also typically varies undesirably when, for example, the properties of the wiper change, for example due to ageing, and is not corrected because the wiper remains in the same position.

The maintenance unit according to the first sub-aspect of the invention is configured to apply a wiping force of a substantially predetermined value, resulting in a constant wiping performance and thus in a more accurate and reliable ink jet system. A wiping force of a substantially predetermined value is obtained by using position control of the set point which cannot be reached by the wiper due to the presence of the print head, in combination with a limitation of the maximum applicable force of the force actuator. As a result, the controller will continuously apply the maximum force to the wiper to urge the wiper toward the position corresponding to the set point. When, for example, the characteristics of the wiper change, the controller will automatically change the position of the wiper so that the maximum force is still applied by the force actuator and no change in wiping performance occurs.

When the wiper does not have to wipe, the setpoint generator is preferably configured to provide the setpoint to a controller corresponding to the position of the wiper at a distance from the surface of the at least one print head, seen in a direction perpendicular to the surface of the at least one print head. In this way, the wiper is placed in the retracted position when no wiping action is required. As a result, when the wiper is required to perform a wiping action, the setpoint generator will once again provide a setpoint corresponding to the position of the wiper, which is at least partially located inside the at least one print head, as seen in a direction perpendicular to the surface of the at least one print head.

In one embodiment, the maintenance unit comprises a wiper moving device for moving the wiper, wherein the controller is connected to the wiper moving device, and wherein the controller is configured to drive the wiper moving device so as to move the wiper along the surface of the at least one print head to remove ink from the surface with the wiper.

Preferably, the force actuator is provided to control only the position in a direction perpendicular to the surface of the at least one print head, thereby only being able to press the wiper against the surface of the at least one print head, while the wiper moving device is provided only to move the wiper parallel to the surface of the at least one print head. In such embodiments, the wiping action is a combination of operating the force actuator and operating the wiper movement device.

In one embodiment, the wiper is guided, i.e. movably supported, by the guiding means relative to the frame in a direction perpendicular to the at least one printhead surface (i.e. parallel to the direction in which the force actuator applies the wiping force). Preferably, the wiper is guided only in said direction. The guide defines a range of movement that allows the wiper to move.

In one embodiment, the maintenance unit comprises a frame (frame), wherein the wiper moving device is configured to operate on the frame of the maintenance unit in order to move the wiper. The force actuator may then be placed between the frame and the wiper so that the moving device is independently controlled with respect to the wiper.

In one embodiment, the force actuator is an electromagnetic actuator, preferably a lorentz actuator (Lorentzactuator), preferably such that the force generated by the electromagnetic actuator is directly proportional to the current applied to the force actuator. The controller may then limit the maximum applicable force of the force actuator by limiting the current applied to the force actuator. Preferably, the current versus force relationship is substantially constant over the range of movement of the wiper, such that the current becomes representative of the force applied over the range of movement.

In one embodiment, the guiding means does not exert a significant force on the wiper in a direction parallel to said wiping force, or in case the guiding means exerts a force, this force is preferably constant and independent of the position of the wiper within the range of movement. The result is that once compensated into a constant force, the force actuator applies a force proportional to the wiping force used to press the wiper against the surface, if necessary. Thus, adjusting the maximum applicable force applied by the force actuator will automatically adjust the wiping force with which the wiper is pressed against the surface

In one embodiment, the guiding means is configured to guide the wiper substantially without hysteresis, for example by using leaf springs (e.g. leaf springs arranged parallel to each other), thereby providing a linear guiding means.

In one embodiment, the force actuator comprises two parts, namely a first part mounted on the frame and a second part mounted on the wiper, wherein the first and second parts interact with each other to exert a force between the first and second parts. For example, the first part may be a coil and the second part may be a permanent magnet interacting with the coil via respective magnetic fields.

In one embodiment, the position sensor is configured to measure a position of the wiper relative to the maintenance unit frame. For example, a position sensor measures the position of the second part relative to the first part. Preferably, the distance between the frame and the at least one printhead face is known and constant, so that measuring the position of the wiper relative to the frame is representative of the position of the wiper relative to the at least one printhead face.

In one embodiment, the wiper moving device is configured to move the wiper in a single direction along the surface. This requires a certain initial alignment between the wiper moving device and the print head surface when a maintenance unit is provided in the inkjet system, but has the advantage that the control of the wiper is relatively simple.

In one embodiment, the wiper width is greater than the width of the surface, wherein the wiper moving device is configured to move the wiper in a longitudinal direction of the surface.

The wiper moving device may additionally be configured to move the wiper in two degrees of freedom, which reduces the required alignment accuracy, but may increase the control requirements.

In one embodiment, the wiper moving device is configured to move the wiper in one or more directions parallel to the at least one printhead surface.

In one embodiment, multiple wipers of a device are provided on a common wiper frame, each wiper moving so that each wiper can move independently of the other wipers. Alternatively, a plurality of wipers may be stably mounted on a common wiper frame, which is integrally moved so as to move the plurality of wipers simultaneously. This considerably reduces the control complexity of the maintenance unit, but does not allow individual control of the wiper movement.

In one embodiment, the wiper frame may be movable in one direction, wherein the wiper moving device is configured to move the individual wipers in another direction, thereby obtaining two degrees of freedom of movement possibilities of the wipers while keeping the control relatively simple.

In one embodiment, after driving the wiper movement device to cause the wiper to perform a wiping action while the wiper frame remains stable relative to the printhead assembly, the wiper frame may be controlled in a stepped manner to position the wiper frame relative to the printhead assembly. After performing the wiping action, the wiper frame may be moved to another position to allow the wiper to perform the wiping action on another print head. Alternatively, the wiper frame may be configured to be moved during a wiping action to engage the wiper moving device to provide the desired movement of the wiper. The manner in which the wiper frame operates may depend on the orientation of the print head. In case all print heads are equally oriented, a stepwise approach may be applied, but when the print heads have different orientations, it may be necessary to move the wiper frame during the wiping action.

In one embodiment, a heating device is provided to heat the wiper. This is particularly advantageous when the ink fluid is a hot melt ink fluid having a melting temperature that exceeds room temperature, as the ink fluid may remain behind the wiper, which may negatively impact the wiping performance of the wiper. By heating the wiper to a temperature above the melting temperature of the ink fluid, the ink fluid can be removed, thereby improving the wiping performance of the wiper.

A first sub-aspect of the fourth aspect of the invention also relates to an inkjet system comprising a print head assembly and a maintenance unit for the print head assembly, the print head assembly comprising at least one print head, wherein the at least one print head is an integrated unit configured to eject ink droplets from nozzles arranged in a surface of the at least one print head towards a substrate, and the maintenance unit is a maintenance unit according to an embodiment of the first sub-aspect of the invention.

In one embodiment, the wiper of the maintenance unit is movable between a maintenance position in which the wiper is capable of performing a wiping action on the at least one print head, and an inoperative position in which the wiper is arranged at a distance from the print head assembly such that the maintenance unit does not interfere with normal printing activities that are typically associated with movement of a substrate beneath the print head assembly.

In one embodiment, the movability of the wiper is provided via a wiper movement device.

Preferably, the movability of the wiper is provided in a plane parallel to at least one print head surface.

In an alternative embodiment, the wiper is stably provided and the print head assembly is moved between an operating position, in which the print head assembly is able to perform printing activities, and a maintenance position, in which the print head assembly is placed close to the maintenance unit to allow maintenance of the at least one print head by the maintenance unit.

The inkjet system may define a print direction that indicates the direction of the substrate past the print head assembly for printing purposes. In one embodiment, the movability of one of the maintenance unit or the print head assembly for maintenance purposes is perpendicular to the printing direction, and preferably in a horizontal direction.

A first sub-aspect of the fourth aspect of the invention also relates to a method of performing maintenance on a print head of a print head assembly, the print head being an integrated unit configured to eject droplets of an ink fluid from nozzles arranged in a print head surface towards a substrate, the method comprising the steps of,

-providing a wiper movable relative to the surface of the print head for removing ink from the surface of the print head,

-pushing the wiper with a force actuator to an unreachable position within the print head while moving the wiper along the surface of the print head;

-keeping the maximum value of the force exerted by the force actuator below a predetermined value while pushing the wiper into said position.

As a result, the wiping force with which the wiper is pressed against the surface of the printhead is substantially constant during the wiping action and will be constant in the future with respect to the subsequent wiping action and therefore independent of the nature of the wiper.

In one embodiment, the ink fluid is purged from the nozzles prior to moving the wiper along the surface of the printhead.

In one embodiment, the wiper is moved to a position away from the printhead face when maintenance is not being performed.

According to a second sub-aspect of the fourth aspect of the invention, the object of the invention is achieved by providing a maintenance unit for an inkjet system having a printhead assembly comprising at least one printhead being an integrated unit configured to eject droplets of an ink fluid from nozzles arranged in a surface of the at least one printhead towards a substrate, wherein the maintenance unit comprises a wiper, wherein the maintenance unit further comprises a force actuator to press the wiper against the surface of the at least one printhead, a force measurement unit configured to determine a wiping force with which to press the wiper against the surface of the at least one printhead, and a controller configured to control the force applied by the force actuator in dependence on an output of the force measurement unit to press the wiper against the surface of the printhead with a predetermined wiping force.

A second sub-aspect of the fourth aspect of the invention is based on the understanding that: an important parameter of the wiping action is the force, i.e. the wiping force with which the wiper is pressed against the surface of the print head, and the wiping force has to be controlled in order to cope with the changing properties of the wiper. If the characteristics of the wiper change due to aging, the wiping force with which the wiper is pressed against the surface of the print head generally also changes. The maintenance unit according to the second sub-aspect of the invention is configured to automatically adjust its settings such that the wiping force is maintained at a predetermined value, resulting in a constant wiping performance and thus in a more accurate and reliable ink jet system.

The difference between the first and second sub-aspects of the fourth aspect of the invention is that more or less predetermined wiping forces are obtained in different ways. In a first sub-aspect of the fourth aspect of the invention, a combination of positional control and limited force application by the force actuator is used to advantage resulting in a predetermined wiping force, while in a second sub-aspect of the fourth aspect of the invention the predetermined wiping force is obtained by appropriately controlling the force applied by the force actuator.

In one embodiment, the maintenance unit comprises a wiper moving device for moving the wiper, wherein the controller is connected to the wiper moving device, and wherein the controller is configured to drive the wiper moving device such that the wiper is moved along the surface of the at least one print head to remove ink from the surface with the wiper.

In one embodiment, the wiper is guided, i.e. movably supported, relative to the frame by the guiding means in a direction parallel to the wiping force producible by the force actuator. Preferably, the wiper is guided only in said direction. The guide defines a range of movement that allows the wiper to move.

In one embodiment, the wiper moving apparatus is configured to operate on a frame of the maintenance unit in order to move the wiper. The force actuator can then be controlled independently of the wiper moving device. In one embodiment, the wiper moving device is configured to move the wiper in a direction perpendicular to a direction of a wiping force that the force actuator can generate.

In one embodiment, the guiding means does not exert a significant force on the wiper in a direction parallel to said wiping force, or in case the guiding means exerts a force, this force is preferably constant and independent of the position of the wiper within the range of movement. The result is that, once compensated to a constant force, the force actuator applies a force proportional to the wiping force used to press the wiper against the surface, if necessary. Thus, adjusting the force applied by the force actuator will automatically adjust the wiping force with which the wiper is pressed against the surface. The force measuring unit is then sufficient to measure the force exerted by the force actuator directly or indirectly.

In one embodiment, the force actuator is an electromagnetic actuator, preferably a lorentz actuator (Lorentzactuator), preferably such that the force generated by the electromagnetic actuator is proportional to the current applied to the force actuator. The force measurement unit can then determine the force applied by the force actuator by measuring the current applied to the force actuator. Preferably, the current versus force relationship is substantially constant over the range of movement of the wiper, such that the current becomes representative of the force applied over the range of movement.

In one embodiment, the guiding means may comprise a resilient member which applies a non-constant guiding force to the wiper, e.g. a guiding force which depends on the wiper position within the range of movement, e.g. a guiding means with spring-like properties. The advantage of the resilient member is that the wiper can be pushed towards the equilibrium position, which is advantageous in particular in the case of a non-operational wiper. However, the guiding force applied by the resilient member may be a significant disturbance force that counteracts the force applied by the force actuator, so that the force applied by the force actuator to the wiper is no longer proportional to the wiping force used to press the wiper against the surface of the printhead.

In order to determine the wiping force with which the wiper is pressed against the surface of the print head, it may be necessary for the force measurement unit to measure a parameter representing the guiding force applied by the guiding means to the wiper and to combine this information with the measured force applied by the force actuator in order to determine the wiping force with which the wiper is pressed against the surface. In case the guiding force exerted by the guiding means depends on the relative position of the wiper with respect to the guiding means, the force measuring unit may comprise a position sensor for measuring said relative position. This allows the controller to drive the force actuator in a manner that can compensate for the guiding force applied by the guiding means.

In other words, the guiding device comprises a resilient member which urges the wiper towards the equilibrium position, wherein the force measuring unit is configured to determine a guiding force applied by the guiding device to the wiper in order to be able to compensate said guiding force by the force actuator. Preferably, the force measuring unit is configured to measure the degree of deviation from the equilibrium position to determine the guiding force applied by the guiding device to the wiper.

In one embodiment, the force measurement unit determines the force applied by the force actuator and from which force the determined guiding force is subtracted to determine the wiping force, which is provided to the controller for control of the wiping force.

In one embodiment, the force actuator can apply a force to the wiper in a direction substantially perpendicular to the surface of the print head.

In one embodiment, the wiper moving device is configured to move the wiper in a single direction along the surface. When a maintenance unit is provided in the inkjet system, this requires a certain initial alignment between the wiper moving device and the print head surface, but has the advantage that the control of the wiper is simple.

In one embodiment, the wiper width is greater than the width of the surface, wherein the wiper moving device is configured to move the wiper in a longitudinal direction of the surface.

The wiper moving device may additionally be configured to move the wiper in two degrees of freedom, which reduces the required alignment accuracy, but may increase the control requirements.

In one embodiment, the wiper moving device is configured to move the wiper in one or more directions parallel to the at least one printhead surface.

In one embodiment, multiple wipers of a device are provided on a common wiper frame, each wiper moving so that each wiper can move independently of the other wipers. Alternatively, a plurality of wipers may be stably mounted on a common wiper frame, which is integrally moved so as to move the plurality of wipers simultaneously. This considerably reduces the control complexity of the maintenance unit, but does not allow individual control of the wiper movement.

In one embodiment, the wiper frame may be movable in one direction, wherein the wiper moving device is configured to move the individual wipers in another direction, thereby obtaining the possibility of two degrees of freedom of movement of the wipers while keeping the control relatively simple.

In one embodiment, after driving the wiper movement device to cause the wiper to perform a wiping action while the wiper frame remains stable relative to the printhead assembly, the wiper frame may be controlled in a stepped manner to position the wiper frame relative to the printhead assembly. After performing the wiping action, the wiper frame may be moved to another position to allow the wiper to perform the wiping action on another print head. Alternatively, the wiper frame must be moved during the wiping action to engage the wiper moving device in order to provide the desired movement of the wiper. The manner in which the wiper frame operates may depend on the orientation of the print head. In case all print heads are equally oriented, a stepwise approach may be applied, but when the print heads have different orientations, it may be necessary to move the wiper frame during the wiping action.

In one embodiment, a heating device is provided to heat the wiper. This is particularly advantageous when the ink fluid is a hot melt ink fluid having a melting temperature that exceeds room temperature, so that the ink fluid may remain behind the wiper, which may negatively impact the wiping performance of the wiper. By heating the wiper to a temperature above the melting temperature of the ink fluid, the ink fluid can be removed, thereby improving the wiping performance of the wiper.

A second sub-aspect of the fourth aspect of the invention also relates to an inkjet system comprising a print head assembly and a maintenance unit for the print head assembly, the print head assembly comprising at least one print head, wherein the at least one print head is an integrated unit configured to eject ink droplets from nozzles arranged in a surface of the at least one print head towards a substrate, and the maintenance unit is a maintenance unit according to an embodiment of the invention.

In one embodiment, the wiper of the maintenance unit is movable between a maintenance position in which the wiper is capable of performing a wiping action on the at least one print head, and an inoperative position in which the wiper is arranged at a distance from the print head assembly such that the maintenance unit does not interfere with normal printing activities that are typically associated with movement of a substrate beneath the print head assembly.

In one embodiment, the noted movability of the wiper is provided via a wiper movement device.

In an alternative embodiment, the wiper is stably provided and the print head assembly is moved between an operating position, in which the print head assembly is able to perform printing activities, and a maintenance position, in which the print head assembly is placed close to the maintenance unit to allow maintenance of the at least one print head by the maintenance unit.

The inkjet system may define a print direction that indicates the direction in which the substrate is passed through the print head assembly for printing purposes. In one embodiment, the movability of one of the maintenance unit or the printhead assembly for maintenance purposes is perpendicular to the printing direction, and preferably in a horizontal direction.

A second sub-aspect of the fourth aspect of the invention also relates to a method of performing maintenance on a print head of a print head assembly, the print head being an integrated unit configured to eject droplets of an ink fluid from nozzles arranged in a print head surface towards a substrate, the method comprising the steps of,

-providing a wiper movable relative to the surface of the print head for removing ink from the surface of the print head,

pressing the wiper against the surface of the print head with a force actuator while moving the wiper along the surface of the print head,

-determining a wiping force with which the wiper is pressed against the surface of the print head by the force actuator,

-driving the force actuator based on the determined wiping force in order to press the wiper onto the surface of the print head with a predetermined substrate wiping force.

In one embodiment, the ink fluid is purged from the nozzles prior to moving the wiper along the surface of the printhead.

In one embodiment, the wiper force is determined indirectly by measuring a parameter of the force actuator representative of the force applied to the wiper by the force actuator when the wiper is guided by the guiding means that introduces substantially no disturbing forces to the wiper.

In one embodiment, when the wiper is guided by a guiding means which introduces a considerable disturbing force to the wiper during the guiding of the wiper, the wiper force is determined indirectly by measuring a parameter of the force actuator which is representative for the force applied to the wiper by the force actuator and by measuring a parameter of the guiding means which is representative for the force applied to the wiper by the guiding means and combining the two measurements.

An embodiment according to the fourth aspect of the invention may be defined by the following 973 prefixed money:

973_1. a maintenance unit for an inkjet system having a print head assembly comprising at least one print head, which is an integrated unit configured to eject droplets of an ink fluid from nozzles arranged in at least one print head surface towards a substrate, wherein the maintenance unit comprises a wiper to wipe along the surface of the at least one print head, characterized in that the maintenance unit further comprises a force actuator to apply a force to the wiper in a direction perpendicular to the surface of the at least one print head, a position sensor to measure the position of the wiper relative to the at least one print head surface, a setpoint generator to generate a setpoint corresponding to a desired position of the wiper relative to the at least one print head surface, as seen in the direction perpendicular to the at least one print head surface, and a controller to drive the force actuator depending on the output of the position sensor and the setpoint, wherein, for wiping along the surface of the at least one print head, the setpoint generator is configured to output a setpoint corresponding to a position of the wiper at least partially inside the at least one print head, and wherein the controller is configured to limit the maximum applicable force of the force actuator to a predetermined value.

973_2. the maintenance unit according to clause 973_1, wherein the maintenance unit comprises a wiper moving device for moving the wiper, and wherein the controller is configured to drive the wiper moving device in such a way that the wiper is moved along the surface of the at least one print head.

973_3. a maintenance unit according to clause 973_1, wherein the maintenance unit comprises a frame and guiding means guiding the movement of the wiper relative to the frame in a direction parallel to the wiping force.

973_4. maintenance unit according to clauses 973_2 and 973_3, wherein the wiper moving device is configured to operate on the frame to move the wiper.

973_5. a maintenance unit according to clause 973_1, wherein the force actuator is an electromagnetic actuator, preferably a lorentz actuator.

973_6. the maintenance unit according to clause 973_3, wherein the guiding means is configured to guide the wiper movement without applying a significant force to the wiper, or the guiding means guides the wiper movement while applying a constant force to the wiper.

973_7. the maintenance unit according to clause 973_2, wherein the wiper moving device is configured to move the wiper with two degrees of freedom in a plane parallel to a surface of the at least one print head.

973_8. maintenance unit according to clause 973_1, wherein a plurality of wipers are arranged on a common wiper frame.

973_9. maintenance unit according to clause 973_8, wherein a respective wiper moving device is provided between the respective wiper and the frame, whereby the movement of each wiper can be independently controlled by the controller.

973_10. a maintenance unit according to clause 973_8, wherein the wiper frame is movable relative to the printhead assembly in only one direction, and wherein a wiper moving device on the wiper frame is configured to move each wiper in a direction different from the one direction of the wiper frame, thereby making the wiper movable in a two-dimensional plane parallel to at least one printhead surface.

973_11. the maintenance unit according to clause 973_1, comprising a heating device for heating the wiper to melt the ink fluid that has accumulated on the wiper and to remove the ink fluid from the wiper.

973_12. maintenance unit for an inkjet system having a print head assembly comprising at least one print head, which is an integrated unit configured to eject droplets of an ink fluid from nozzles arranged in a surface of the at least one print head towards a substrate, wherein the maintenance unit comprises a wiper, characterized in that the maintenance unit further comprises a force actuator for pressing the wiper against the surface of the at least one print head, a force measurement unit configured to determine a wiping force for pressing the wiper against the surface of the at least one print head, and a controller configured to control a force applied by the force actuator in dependence on an output of the force measurement unit so as to press the wiper against the surface of the print head with a predetermined wiping force.

973_13. an inkjet system comprising a printhead assembly having at least one printhead, the printhead being an integrated unit configured to eject droplets of an ink fluid from nozzles disposed in a surface of the at least one printhead toward a substrate, wherein the inkjet system further comprises a maintenance unit according to one or more of clauses 973_1-973_12 to perform maintenance on the at least one printhead.

973_14 an ink jet system according to clause 973_13, wherein the wiper of the maintenance unit is movable between an operating position in which the wiper is able to perform a wiping action with respect to the at least one print head, and a non-operating position in which the wiper is arranged at a distance from the print head assembly, such that the maintenance unit does not interfere with normal printing activities.

973_15 an ink jet system according to clause 973_14, wherein the printing direction is defined to correspond to a direction of passage of the substrate through the print head assembly for printing purposes, and wherein the maintenance unit is movable in a horizontal direction perpendicular to the printing direction.

973_16. a method of performing maintenance on a printhead of a printhead assembly, the printhead being an integrated unit configured to eject drops of ink fluid from nozzles disposed in a printhead surface toward a substrate, the method comprising the steps of:

-providing a wiper movable along a surface of the print head to remove ink from said surface;

-pushing the wiper with a force actuator to an unreachable position within the print head while moving the wiper along the surface of the print head;

-keeping the maximum value of the force exerted by the force actuator below a predetermined value while pushing the wiper into said position.

973_17. a method of performing maintenance on a printhead of a printhead assembly, the printhead being an integrated unit configured to eject drops of ink fluid from nozzles disposed in a printhead surface toward a substrate, the method comprising the steps of:

-providing a wiper movable along a surface of the print head to remove ink from said surface;

-pressing the wiper against the surface of the print head with a force actuator while moving the wiper along the surface of the print head;

-determining a wiping force with which the wiper is pressed against the surface of the print head by the force actuator;

-driving the force actuator based on the determined wiping force in order to press the wiper onto the surface of the print head with a predetermined wiping force.

973_18. the method according to clauses 973_16 or 973_17, wherein the ink fluid is purged from the nozzles before moving the wiper along the print head surface.

A fifth aspect of the invention will now be explained.

A fifth aspect of the present invention relates to an inkjet system and method for printing an ink pattern on a substrate by using the inkjet system and based on a received pattern layout. The method can be applied to any situation where a homogeneous, smooth-walled (smooth-walled) feature in a printed wiring diagram is required. The ink pattern is a two-dimensional pattern. In particular, the ink pattern is an Integrated Circuit (IC) pattern. Inkjet technology is used to print ink patterns.

Printed Integrated Circuit (IC) printing, including printed circuit boards, is an emerging technology that attempts to reduce the costs associated with IC production by replacing expensive photolithography with simple printing operations. IC printing systems can significantly reduce IC production costs by printing IC patterns directly on a substrate without the use of sophisticated and time consuming lithography used in conventional IC manufacturing. The printed IC pattern may contain actual IC features (i.e., elements to be incorporated into the final IC, such as gate and source and drain regions of thin film transistors, signal lines, optoelectronic device elements, etc., or it may be a mask (e.g., etched, implanted, etc.) for subsequent semiconductor processing.

Typically, IC printing involves depositing a printing solution through a solid substrate by rastering a bitmap along a single axis of print movement ("print direction"). Print heads (especially arrangements incorporating one or more ejectors in those print heads) are optimized for printing along this print movement axis. Printing of the IC pattern is performed in a raster fashion, with the print head performing a "print pass" over the substrate as one or more jets in the print head dispense individual drops of printing solution onto the substrate. Typically, at the end of each print pass, the print head makes a vertical shift relative to the print movement axis before starting a new print pass. A plurality of print heads continuously print passes over the substrate in this manner until the IC pattern is completely printed.

Once dispensed from one or more jets of the print head, the drops of printing solution attach themselves to the substrate by wetting and continue to solidify in place. The size and profile of the deposited material is guided by the simultaneous process of solidification and wetting. Depending on the type of ink, the ink is solidified by polymerization, crystallization, heat transfer by infrared radiation, and the like. In the case of printing phase change materials for etch mask production, solidification occurs when the printed ink droplets transfer their thermal energy to the substrate and revert to solid form. In another case, a suspension such as a colloidal suspension of an organic polymer and an electronic material in a solvent or carrier is printed and wetted onto the substrate leaving printed features. The temperature conditions and material properties of the printing solution and the substrate, along with ambient atmospheric conditions, determine the specific ratio of the deposited printing solution to change from a liquid to a solid.

If a first ink drop and a second adjacent ink drop are applied to a substrate in one go before the phase change of the first ink drop, the second ink drop will wet in its liquid or semi-liquid state and coalesce to the first ink drop, forming a continuously printed feature.

When a printed feature is printed in a single print pass (so-called line) in the print direction, adjacent ink drops will be deposited during the single print pass and there will be no time for drying between jetting events. The desired uniformity and smooth sidewall profile results in when optimal droplet coalescence occurs. However, raster printing in a direction perpendicular to the printing direction, in particular, often results in ink patterns having scalloped edges. An ink pattern extending in a direction perpendicular to the printing direction is a typical "multi-pass" feature; that is, the print features are formed by multiple passes (known as multiple rows) of the print head. In a multi-pass feature, ink drops deposited during a continuous pass of the print head are typically dried before any adjacent ink drops from the next print pass are deposited. Consequently, drops of printing solution that make up for multiple passing features cannot coalesce and thus create "scalloped" feature boundaries. This scalloping of the edges can be recognized as separate drops of printing solution used to form the ink pattern are all clearly visible.

Such edges becoming scalloped is associated with a variety of difficult events. For example, if the IC pattern is a mask, irregular edge features can lead to unreliable print quality and pattern defects, which lead to inconsistent device performance. Perhaps more significantly, the edge becoming scalloped indicates a potentially serious underlying defect in real IC features. The electronic properties of an IC feature are affected by its molecular structure. In particular, the molecules of organic printing liquids are typically long chains, which need to self-assemble in a specific order. However, if the drops of such printing solution solidify before adjacent drops are deposited, those chains do not combine properly, resulting in a significant reduction in electrical continuity between the two drops. This in turn can severely impair the performance of devices embodying scalloped printing features.

EP1.392.091 discloses a printing system and method to reduce scalloping effects, but the printing system and method are still unsatisfactory. The disclosed method separates an ink pattern into a first design layer and a second design layer. The first design layer is comprised of features running parallel to a first reference axis aligned with the print direction. The second design layer is comprised of features that run parallel to a second reference axis that is not parallel to the printing direction. The second design layer is printed after the first design layer is printed. The printed pattern may be formed by a series of printing operations, wherein the printing direction of each printing operation is aligned with the parallel layout features of the design layer being printed.

A disadvantage of this method is that it does not provide a satisfactory solution for ink patterns having curved geometries. In particular, a round ink pattern may still have scalloped edges. IC printing includes a plurality of circular ink patterns, particularly at the connection sites at the ends of the circuit rows, for electrically connecting IC components.

A general object of the present fifth aspect of the invention is to at least partly obviate the above disadvantages and/or to provide a usable alternative. More specifically, it is an object of a fifth aspect of the present invention to provide a method for printing an ink pattern, wherein the resulting ink pattern has an increased uniformity and improved smooth sidewalls. A particular object is to obtain an ink pattern with a more accurate outer contour.

According to a fifth aspect of the present invention, this object is achieved by a method for printing an ink pattern according to clause 974_1.

According to a fifth aspect of the present invention, there is provided a method of printing an ink pattern on a substrate based on a pattern layout. In one step of the method, the pattern layout is separated into a discrete outline layer and a discrete inner region layer. In at least one step, the pattern layout is divided into one discrete profile layer comprising at least one profile portion. Further, the pattern layout is separated in at least one discrete inner zone layer comprising at least one inner zone portion. An imaginary X-Y plane is defined for the ink jet system used, which includes a first (X) and a second (Y) axis. The first axis X is defined relative to the inkjet system to extend in a direction perpendicular to a moving direction of the linearly movable substrate positioning stage. The second axis Y is oriented perpendicular to the first axis X and is in projection on the inkjet system in a direction parallel to the movement of the linearly movable substrate positioning stage. Each contour portion of the contour layer of the pattern layout has an orientation in an imaginary X-Y plane. Each outline portion of the selectable portion of the pattern layout has an accompanying inner region portion. At least one outline portion of the selectable portion of the pattern layout having a non-parallel orientation with respect to the Y-axis is printed by outline ink drops prior to printing the inner area portion of the inner area layer of the selectable portion of the pattern layout by filling ink drops. Preferably, at least one of the profile sections has an orientation parallel to the X-axis.

In the method according to the fifth aspect of the invention, an inkjet system is used. The inkjet system receives a pattern layout, in particular an image file. The image file is, for example, a bitmap. The pattern layout may be received from an information carrier, such as a USB stick, CD-rom, etc., or provided via a network connection. The ink jet system contains control electronics for controlling the ink jet system. The control electronics include software for separating the received pattern layout into an outline layer and an inner zone layer. The profile layer is defined separately from the inner zone layer. In the method according to the invention, the contour layer is printed in a first step, wherein the inner zone layer is printed later on in a next step.

The method according to the fifth aspect of the invention is based on an understanding of the interaction mechanism between adjacent ink droplets after deposition on a substrate. The interaction mechanism is a relevant factor in the accuracy of the finally obtained ink pattern.

The ink pattern is composed of a number of adjacent ink drops that will recombine to achieve the desired shape. In inkjet systems, ink droplets are typically deposited in a structured process. Ink drops are typically deposited in a plurality of rows in the printing direction, which is the direction of movement of the substrate. The plurality of rows are placed in series parallel to each other. Adjacent pairs of drops in the same row have a particular interaction mechanism with each other that is different from the interaction mechanism between adjacent drops of successive rows. Between the ink drops in a row, they are deposited shortly after each other to form the row. The deposition time interval for adjacent drops in the same row is typically about 0.1 megaseconds (msec). After the ink drop is deposited, the ink drop begins to solidify and changes from a wet state to a solid state. Solidification occurs in the time interval after deposition and may occur, for example, 10 seconds. The deposition time interval for adjacent drops in successive rows is typically more than 10 seconds, which is much longer than the deposition time interval for adjacent drops in the same row. This difference in time interval leads to another flow behavior and thus to another interaction mechanism between adjacent drops. Due to the different interactions of the ink droplets, the resulting ink pattern changes its geometry as the ink droplets recombine. At a first location in the ink pattern, adjacent ink drops may have started coalescing after a few milliseconds, while at a second location, adjacent ink drops may have started coalescing after, for example, 10 seconds. For that reason, the ink pattern becomes a worse accurate display of the pattern layout.

Advantageously, the method according to the invention reduces this negative effect of different interactions. According to the present invention, the pattern layout is separated into an outline and an inner area, wherein the outline is printed before the inner area is printed. The accuracy of the contour of the obtained ink pattern largely determines whether the ink pattern is an acceptable display of the pattern layout. By printing the outline first, a more accurate outer dimension of the obtained pattern is achieved. The effect of the edge scalloping is also reduced.

Specifically, the contour is first printed by depositing contour ink droplets, and thereafter the inner region is filled with filler ink droplets before the ink solidifies. The outline of the ink pattern primarily determines the accuracy. Advantageously, the contours are generated relatively quickly, whereby the variation of the ink flow behavior remains limited, which results in a more accurate ink pattern.

The pattern layout may represent the entire IC pattern, but may also represent a portion of the IC pattern. The pattern layout may be separated in at least one step. The entire pattern layout can be separated into contours and inner regions in one step. Alternatively, the entire pattern layout may be separated into at least one contour layer and at least one inner zone layer in a plurality of steps. The pattern layout of the entire IC pattern may be subdivided into a set of pattern layout layers prior to printing. Subsequently, according to a fifth aspect of the present invention, each pattern layout layer is considered as an independent pattern layout and is separated into a discrete outline and an inner area, wherein the outline of the pattern layout part is printed before the inner area of the pattern layout part.

In an embodiment according to the fifth aspect of the invention, the received pattern layout is separated into discrete contours and discrete inner regions in one step. The ink pattern is printed by first printing discrete contours and then printing the inner area.

In an embodiment of the method according to the fifth aspect of the invention, the pattern layout comprises at least two pattern layout layers, which are printed in successive printing steps. Each pattern layout layer is printed by printing an outline before printing an inner region of the pattern layout layer.

In a particular embodiment of the method according to the invention, the pattern layout may comprise at least two pattern layout layers, wherein the first pattern layout layer is printed with a constant X-coordinate. The overall pattern layout is subdivided into a set of pattern layout layers based on the substrate's travel movement in the inkjet system. In the first printing step, the X coordinate is kept constant by preventing the substrate from moving in the X direction (X-direction). After the substrate is displaced in the X-direction, a subsequent second pattern layout layer is subsequently printed in a second printing step. The shift may be a distance of at most 100 μm in the X-direction, in particular at most 0.50 μm, but preferably at most 0.25 μm. The first pattern layout layer is printed by first printing the outline and then printing the inner region of the first pattern layout layer. Accordingly, the first pattern layout layer is completely printed. Subsequently, the second pattern layout layer is printed by first printing the outline and then printing the inner region of the second pattern layout layer. Thus, the second pattern layout layer is completely printed after the first pattern layout layer is completely printed. It is advantageous to complete the pattern layout layer before printing the next pattern layer by printing both the outline as well as the inner area, as this can reduce the total printing steps to complete the ink pattern. The entire ink pattern can be printed in a shorter printing time.

In a particular embodiment of the method according to the invention, the pattern layout may comprise at least two pattern layout layers, wherein a first pattern layout layer comprises a first class of contour types and wherein a second pattern layout layer comprises a second class of contour types. The particular classification of the shape depends on the orientation of at least a portion of the contour as described hereinafter. A first layout layer comprising a first category of outlines may be fully printed, wherein both outlines and inner areas are included before starting the printing step of printing a second pattern layout layer comprising a second category of outlines to obtain a final ink pattern corresponding to the received pattern layout. The class of profile types may be characterized by a specific time interval for depositing ink drops. The speed of the substrate positioning stage may correspond to the type of profile that must be thrown. The ink pattern may be generated by successively printing the first and second pattern layout layers.

Advantageously, by subdividing the received pattern layout into several pattern layout layers based on the categories of the outline types, the total printing time to print all of the ink patterns may be reduced. According to a fifth aspect of the present invention, each of the plurality of pattern layout layers is considered an individual pattern layout, wherein each individual pattern layout is divided into discrete outlines and discrete inner areas, wherein the outlines of the pattern layout are printed by outline ink drops before the inner areas of the pattern layout are printed by filling ink drops.

In a particular embodiment of the method according to the invention, the pattern layout may be subdivided into a set of pattern layout features before printing the ink pattern. One feature may be, for example, a connection point for an electrical component on a printed circuit board. Such features have a typical circular geometry. The pattern layout features are divided into discrete outlines and discrete inner regions. The outline of the pattern layout layer feature is printed before the inner region of the pattern layout feature is printed.

In an embodiment of the method according to the fifth aspect of the invention, the pattern layout is divided into a profile layer and an inner area layer. In particular embodiments, the pattern layout may contain only contours. After applying logic to separate the pattern layouts, the inner area may appear to be a blank area, thereby making it possible to omit printing of the inner area.

In an embodiment of the method according to the fifth aspect of the invention, the contour layer of the pattern layout is printed by depositing contour droplets before the inner area layer of the pattern layout is printed by depositing fill droplets. The full contour portion is printed before the inner area portion. Advantageously, there are no exceptions that need to be programmed in the control electronics for having the profile portions oriented parallel to the Y-axis.

In an embodiment of the method according to the fifth aspect of the invention, a contour printing algorithm is applied for printing the contour, wherein the contour printing algorithm converts the contour into a set of drop positions. The ink jet system used includes control electronics to control the system. The control electronics contain software configured to convert the received pattern layout into a set of drop positions. The software includes logic for separating the pattern layout into discrete contours and inner regions. The logic includes a contour printing algorithm. The outline of the pattern layout is converted into a set of drop locations by applying an outline printing algorithm. In the next step, the ink jet system is operated to deposit a contour drop at the calculated drop position.

In an embodiment of the method according to the fifth aspect of the invention, the method comprises the step of defining an orientation of at least a part of the outline of the pattern layout. The orientation of the profile is defined by an angle in a plane relative to the reference axis. In particular, the reference axis corresponds to the printing direction of the inkjet system. The printing direction of the inkjet system may be defined by the direction of movement of the substrate positioning table through which the print head is moved.

For example, the contour or a portion of the contour may be a line. The orientation of the line can be determined by measuring the angle between the line and the reference axis. The orientation of at least a part of the outline of the pattern layout may be defined by determining at least two-dimensional position coordinates of the outline in a cartesian coordinate system. The orientation may be determined by subtracting the position coordinates.

For example, the profile or a portion of the profile may be arcuate in shape. The orientation of the arc-shaped profile can be determined by measuring the angle between the tangent and the reference axis.

Based on the obtained orientation of at least a part of the contours, at least a part of the contours are then classified in a corresponding contour class of the classification system.

In a subsequent step of the method, an outline printing algorithm is selected according to the classified outline class. By applying the selected contour printing algorithm, at least part of the contour of the pattern layout is converted into a set of contour drop positions and at least part of the contour drops of the contour are printed onto the substrate.

By using a dedicated contour printing algorithm for several classes of classification systems, it can be used to account for ink flow characteristics that depend on a portion of the pattern layout orientation. Advantageously, it is thereby possible to manufacture more accurate ink patterns.

In an embodiment of the method according to the fifth aspect of the invention, the profile classification is characterized by an orientation of the profile in an imaginary plane comprising a first X-axis and a second Y-axis oriented in-plane, wherein the first axis is defined as a linear movement perpendicular to the substrate during operation, wherein the second axis Y is oriented perpendicular to the first axis X and in projection on an inkjet system, which is in a moving direction parallel to the linearly movable substrate positioning stage.

In an embodiment of the method according to the fifth aspect of the invention, the sorting system comprises a first profile sort, a second profile sort and a third profile sort, wherein the first, second and third profile sorts comprise the profile orientation in a first quadrant of a cartesian coordinate system comprising X and Y axes, wherein the Y axis corresponds to the printing direction of the inkjet system as the moving direction of the substrate.

The first contour classification (I) corresponds to a set of contour portions oriented in quadrant regions delimited by a direction parallel to the X-axis and a direction less than a predetermined angle with respect to the Y-axis. The first profile class I can also be denoted as X-X \ orientation, where the orientation is aligned with the reference axis in the X-direction, the X-axis, or less than a certain tilt with respect to the X-axis, the X' -axis.

The second contour classification (II) corresponds to a set of contour portions oriented in a quadrant region between a direction smaller than the predetermined angle α and a direction parallel to the Y-axis. The second classification may also be represented as a set of contour portions having an X-Y orientation.

The third profile class (III) corresponds to a set of profile portions oriented in a direction parallel to the Y-axis. The third category may also be represented as a set of contour portions having a Y orientation.

In an embodiment of the method according to the fifth aspect of the invention, the classification system comprises additional classifications corresponding to orientations in the second, third and/or fourth quadrant of a cartesian coordinate system.

In an embodiment of the method according to the fifth aspect of the invention, the method comprises converting the defined orientation of at least a part of the outline of the pattern layout into an orientation falling within the first quadrant. This conversion into the first quadrant may be obtained by mirroring the orientation about the first and/or second reference axis. After applying the selected contour printing algorithm, at least a portion of the contour of the pattern layout is converted into a set of contour drop positions. Subsequently, the set of contour drop positions determined for the first quadrant is reconverted to the second, third, or fourth quadrant. After recovery, the final set of positions is obtained and the at least partially contoured outline ink drops are ready to be printed onto the substrate.

In an embodiment of the method according to the fifth aspect of the invention, the contour printing algorithm comprises an overlay algorithm for converting at least a part of the contour into a set of overlay elements before generating the set of drop positions. Instead of transforming directly from the pattern layout to a set of positions in one step, an intermediate step is introduced to transform a part of the outline of the pattern layout into at least one overlay element. Subsequently, the calculations defined by the algorithm are performed on the overlay elements. The overlay element may be a simplified form of at least a portion of the outline. The cover elements may be, for example, wire, arc or circular elements. Preferably, the covering elements are line-like elements, also called strip-like elements. Advantageously, by applying the overlay algorithm as a feature of the contour printing algorithm, the contour printing algorithm is simplified. By converting at least part of the outline into an overlay element, many of the calculations in the outline printing algorithm may be reduced. The computational power burden of the control electronics is less. Advantageously, the ink jet system may have increased speed and throughput.

In an embodiment of the method according to the fifth aspect of the invention, the contour printing algorithm of the first contour classification I comprises an overlay algorithm comprising at least one of the following parameters: defining parameters for a plurality of ink drops; parameters defining ink drop size; a parameter defining a constant mutual distance between the ink drops; and a parameter defining at least one absolute drop position.

The result of the overlay algorithm of the first contour classification may be a strip-shaped element as an overlay element. The strip-shaped elements have an orientation in the X direction. The strip-like elements may extend under an angle in the X-direction. The band is composed with a constant mutual distance between the drops.

In an embodiment of the method according to the fifth aspect of the invention, the contour printing algorithm of the second contour classification comprises an overlay algorithm comprising at least one of the following parameters: parameters defining ink drop size; a parameter defining at least one absolute drop position; defining parameters for a number of ink drops extending in the Y direction at the X position; and a parameter defining a mutual distance between at least one of the drops as a function of absolute drop placement.

The result of the overlay algorithm of the second contour classification may be a strip-shaped element as an overlay element. The belt may be an inclined belt. Preferably, the cover element is a strip-like element having an orientation in a direction parallel to the Y-axis.

The band is composed of varying mutual distances between the ink drops over a profile of a certain length. Advantageously, the varying mutual distance between the ink drops allows a more precise profiling of the ink pattern.

In an embodiment of the method according to the fifth aspect of the invention, the contour printing algorithm of the third contour classification comprises an overlay algorithm comprising at least one of the following parameters: defining parameters for a plurality of ink drops; a parameter defining a constant mutual distance between the ink drops for at least a part of the contour; and a parameter defining at least one absolute drop position.

The result of the overlay algorithm of the third contour classification may be a strip element as an overlay element. The strip-shaped elements have an orientation in the Y direction. The strip-shaped elements are composed with a constant mutual distance between the ink drops.

In an embodiment of the method according to the fifth aspect of the invention, the contour printing algorithm of the first contour classification comprises an overlay algorithm comprising parameters defining a distance between contour drops and fill drops. Thereby, two adjacent cover elements can be accurately positioned, taking into account ink flow effects that occur when two cover elements comprising a specific orientation are placed adjacent to each other.

In an embodiment of the method according to the fifth aspect of the invention, an inner area printing algorithm is applied to print the inner area of the pattern layout by filling ink drops. The inner region printing algorithm converts the inner region into a set of fill drops. Similar to the outline printing algorithm described above, the inner region printing algorithm may also include an overlay algorithm for converting at least a portion of the inner region into a set of overlay elements prior to generating the set of fill drop locations. Preferably, the cover element is a strip element having an orientation in the Y direction. In an embodiment of the method according to the fifth aspect of the invention, the contour printing algorithm comprises an ink flow algorithm for taking into account ink flow effects prior to generating the set of drop positions. The ink flow effect may depend, for example, on the combination of ink and substrate applied or the time interval for depositing adjacent ink droplets. Advantageously, incorporating the ink flow algorithm into the contour printing algorithm improves the accuracy of the resulting ink pattern.

In an embodiment of the method according to the fifth aspect of the invention, both the overlay algorithm and the ink flow algorithm may be incorporated into the contour printing algorithm. In a first step of the outline printing algorithm, the outline of the pattern layout may be converted to a specific overlay element. In a subsequent step, the covering element is converted into a set of drop positions, taking into account the flow behavior of the drops used to form the particular covering element in dependence on the current situation. The type of ink and substrate material, for example, may be considered when determining a set of drop locations for a particular overlay element. Advantageously, incorporating both the overlay and ink flow algorithms into the contour printing algorithm improves the accuracy of the resulting ink pattern.

In an embodiment of the method according to the fifth aspect of the invention, the ink flow algorithm comprises measuring an ink flow parameter originating from at least one test pattern. In this method, the ink flow parameters are determined by comparing a printed test pattern to a desired pattern (pattern layout).

The test pattern may comprise at least one overlay element. In particular, the test pattern includes a pair of overlay elements positioned adjacent to one another to determine ink flow effects between the pair of overlay elements to define ink flow parameters considered by the measured ink flow effects. The ink flow effect may be a finite effect or a time-dependent effect, which may be compensated for, for example, by adjusting the ink drop size or positioning. Preferably, the measurements are performed in an inkjet system, wherein the inkjet system comprises a calibration scanning unit for capturing images of the printed test pattern. Advantageously, an on-line measurement may be performed to determine the ink flow parameter.

In an embodiment of the method according to the fifth aspect of the invention, the width of the test pattern is measured and compared to the pattern layout to determine the defect and to determine the ink flow parameter to compensate for the defect.

In an embodiment of the method according to the fifth aspect of the invention, the result of the ink flow algorithm determines a predetermined angle α as the borderline between the first and the second classification of the classification system. Advantageously, the contour printing algorithm can be optimized by optimizing the utilization of different overlay elements.

In an embodiment of the method according to the fifth aspect of the invention, the result of the ink flow algorithm determines a value of a parameter of the overlay algorithm.

Furthermore, a fifth aspect of the present invention relates to an inkjet system, in particular a drop on demand inkjet system for industrial applications. The inkjet system is arranged to print an ink pattern, in particular an IC pattern, on a substrate. The ink jet system includes at least one ink jet print head for ejecting ink droplets onto a substrate. The inkjet system comprises a substrate positioning stage for conveying and moving the substrate. The ink jet system also includes control electronics for controlling the ink jet system. The control electronics contain software configured to apply the method according to the fifth aspect of the invention for printing an ink pattern onto a substrate based on the received pattern layout. The software includes logic for separating the pattern layout into discrete contours and inner regions. The software includes logic for extracting discrete contours and discrete inner regions from the received pattern layout. The control electronics are programmed to print the outline of the pattern layout by outlining the ink drops before printing the inner area of the pattern layout by filling the ink drops.

An embodiment according to the fifth aspect of the invention may be defined by the following clause with the 974 prefix:

974_1. method for printing an ink pattern on a substrate based on a received pattern layout by using an inkjet system, wherein the pattern layout is divided in at least one step into at least one discrete contour layer comprising at least one contour portion and at least one discrete inner region layer comprising at least one inner region portion, wherein the at least one contour portion has an orientation in an imaginary plane comprising a first (X) axis and a second (Y) axis, wherein the first axis is defined with respect to the inkjet system to extend in a direction perpendicular to a moving direction of a linearly movable substrate positioning stage and wherein the second axis is oriented perpendicular to the first axis parallel to the moving direction of the linearly movable substrate positioning stage, wherein, before printing the inner region portion of the inner region layer of a selectable part of the pattern layout by filling ink droplets, at least one outline portion having a selectable portion of the pattern layout oriented non-parallel with respect to the Y-axis is printed by outline ink drops.

974_2. the printing method according to clause 974_1, wherein a contour printing algorithm is applied for printing the contour, wherein the contour printing algorithm converts the contour into a set of contour drop positions.

974_3. a method according to clauses 974_1 or 974_2, wherein the method comprises the steps of:

-defining an orientation of at least the contour portion of the pattern layout;

-classifying the at least contour portion according to the orientation defined in the corresponding contour classification in the classification system;

-selecting a contour printing algorithm according to the classified contour classification; and is

-printing contour drops of at least a contour portion of the pattern layout by applying the selected contour printing algorithm.

974_4. the method according to clause 974_3, wherein the profile classification is characterized by: the orientation of the contour portion in an imaginary plane comprising the plane is oriented in an imaginary plane comprising a first (X) axis and a second (Y) axis, wherein the first axis is defined with respect to the inkjet system as extending in a direction perpendicular to a direction of movement of the linearly movable substrate positioning stage, wherein the second axis Y is oriented perpendicular to the first axis X and in projection on the inkjet system, the inkjet system is in a direction of movement parallel to the linearly movable substrate positioning stage.

974_5. a method according to clause 974_3 or 974_4, wherein the sorting system comprises a first profile class I, a second profile class II and a third profile class III, wherein the first, second and third profile classes comprise a profile orientation in a first quadrant of a cartesian coordinate system comprising X and Y axes, wherein the Y axis corresponds to a printing direction in projection on the inkjet system parallel to a moving direction of the linearly movable substrate positioning table, wherein the first profile class (I) corresponds to a set of profile portions oriented in a quadrant region delimited by a direction parallel to the X axis and a direction smaller than a predetermined angle relative to the Y axis; wherein the second contour classification (II) corresponds to a set of contour portions in a quadrant region oriented between a direction smaller than the predetermined angle α and a direction parallel to the Y-axis; wherein the third profile class (III) corresponds to a set of profile portions oriented in a direction parallel to the Y-axis.

974_6. the method according to any of the clauses 974_2-974_5, wherein the contour printing algorithm comprises an overlay algorithm for converting the at least one contour portion into a set of at least one overlay element before generating the set of drop positions.

974_7. according to the method of clause 974_6, the overlay element is a strip-like element having an orientation in a direction parallel to the Y-axis.

974_8. the method according to clauses 974_6 or 974_7, wherein the contour printing algorithm of the first contour classification (I: X-X' orientation) comprises an overlay algorithm comprising at least one of the following parameters:

-defining parameters for a plurality of ink drops;

-a parameter defining the size of the ink drop;

-a parameter defining a constant mutual distance between the drops; and

-a parameter defining at least one absolute drop placement.

974_9. the method according to any of the clauses 974_6-974_8, wherein the contour printing algorithm of the first contour classification I comprises an overlay algorithm comprising parameters defining the distance between contour drops and fill drops.

974_10. the method according to clauses 974_6 or 974_7, wherein the contour printing algorithm of the second contour classification (II: X-Y orientation) comprises an overlay algorithm comprising at least one of the following parameters:

-a parameter defining the size of the ink drop;

-a parameter defining at least one absolute drop placement;

-defining parameters of a plurality of ink drops extending in the Y direction at the X position; and

-defining at least one mutual distance between the drops as a parameter as a function of the absolute drop position.

974_11. the method according to clauses 974_6 or 974_7, wherein the contour printing algorithm of the third contour classification (III: Y orientation) comprises an overlay algorithm comprising at least one of the following parameters:

-a parameter defining the size of the ink drop;

-a parameter defining a constant inter-drop mutual distance for at least a part of the contour;

-a parameter defining at least one absolute drop placement.

974_12. the method according to any of the preceding items, wherein the printing algorithm comprises an ink flow algorithm for taking into account ink flow effects prior to generating the set of drop positions.

974_13. the method according to clause 974_12, wherein the ink flow algorithm comprises an ink flow parameter initiated by measuring at least one test pattern.

974_14. the method according to clause 974_13, wherein the test pattern comprises at least one overlay element.

974_15. the method according to clause 974_13, wherein the overlay element is a strip-like element having an orientation in a direction parallel to the Y-axis.

974_16. the method according to any of the clauses 974_13-974_15, wherein the test pattern comprises a pair of overlay elements positioned adjacent to each other to determine an ink flow effect between the pair of overlay elements to define the ink flow parameter under consideration for the measured ink flow effect.

974_17. the method according to any of the clauses 974_12-974_16, wherein the measurement is performed in an inkjet system, wherein the inkjet system comprises a calibration scan unit for capturing images of printed test patterns, wherein the ink flow parameters are determined by comparing the printed test patterns and the pattern layout.

974_18. the method according to any of the clauses 974_12-974_17, wherein the width of the test pattern is measured and compared to the pattern layout to determine a defect to determine the ink flow parameters to compensate for the defect.

974_19. the method according to any of the clauses 974_5-974_18, wherein the result of the ink flow algorithm determines a predetermined angle α as the boundary between the first classification and the second classification.

974_20. the method according to any of the clauses 974_11-974_19, wherein the result of the ink flow algorithm determines the value of a parameter of the overlay algorithm.

974_21 ink jet system, in particular for drop-on-demand printing of ink patterns on substrates for industrial applications, comprises

An inkjet print head for ejecting ink droplets onto a substrate;

a substrate positioning stage for transferring and moving a substrate;

control electronics for controlling an inkjet system, wherein the control electronics are configured to perform a method according to any of clauses 974_1-974_19, comprising: software configured to apply a method for printing an ink pattern on a substrate based on a received pattern layout, wherein the pattern layout is divided into discrete outlines and discrete inner regions, wherein the outlines of the pattern layout are printed by outline ink drops before the inner regions of the pattern layout are printed by filling ink drops, wherein the software comprises logic for extracting the discrete outlines and the discrete inner regions from the received pattern layout.

974_22. printing an integrated circuit pattern, particularly a pattern layout for a Printed Circuit Board (PCB), using a method according to any of the clauses 974_1-974_ 20.

A sixth aspect of the invention will now be explained.

A sixth aspect of the invention relates to an inkjet system, in particular an IC inkjet system for printing integrated circuits, and a method for calibrating and controlling a substrate holder with respect to a virtual plane, wherein the virtual plane is parallel to an imaginary plane formed by the common positions of a set of nozzles of a print head.

Integrated Circuit (IC) printing, and particularly the printing of printed circuit boards, is an emerging technology that attempts to reduce the costs associated with IC production by replacing expensive lithographic processes with simple printing operations. IC printing systems can significantly reduce IC production costs by printing IC patterns directly on a substrate without the use of sophisticated and time consuming lithography used in conventional IC manufacturing. The printed IC pattern may contain actual IC features (i.e., elements to be incorporated into the final IC, such as gate and source and drain regions of thin film transistors, signal lines, optoelectronic device elements, etc., or it may be a mask (e.g., etch, implant, etc.) for subsequent semiconductor processing.

Typically, IC printing involves depositing a printing solution through a substrate by rastering a bitmap along a single axis of print movement ("print direction"). Print heads (especially arrangements incorporating one or more ejectors in those print heads) are optimized for printing along this print movement axis. Printing of the IC pattern is performed in a raster fashion, with the print head performing a "print pass" over the substrate as one or more jets in the print head dispense individual drops of printing solution onto the substrate. Typically, at the end of each print pass, the print head makes a vertical shift relative to the print movement axis before starting a new print pass. A plurality of print heads continuously print passes over the substrate in this manner until the IC pattern is completely printed.

A disadvantage of this background is that the accuracy of such IC printing systems is limited. The accuracy of IC printing systems is limited due to deviations that occur during the printing movement of the print head and the substrate. Misalignment is typically introduced by the guides and bearings of the IC printing system.

A general object of the present sixth aspect of the invention is to at least partly obviate the above disadvantages and/or to provide a usable alternative. More specifically, an object of the sixth aspect of the present invention is to provide an ink jet system including a relatively simple configuration but having high accuracy performance and a method for controlling the positioning of a substrate in the ink jet system with high accuracy.

According to a sixth aspect of the invention, this object is achieved by an ink jet system according to clause 975_1.

According to a sixth aspect of the present invention, there is provided an ink jet system for printing an ink pattern onto a substrate. The inkjet system includes a substrate holder for holding a substrate.

Furthermore, the inkjet system comprises a substrate positioning stage for positioning the substrate holder in the printing direction. The printing direction is defined as the direction of travel of the substrate positioning stage with respect to the longitudinal axis of the ink jet system. The print direction of an inkjet system may be defined as the direction of movement of the substrate as it passes the print head assembly in order to print a row onto the substrate. The substrate holder is supported by a substrate positioning stage.

Further, the inkjet system includes a stage positioning apparatus. The substrate positioning stage may be moved by a stage positioning device. In particular, the substrate positioning table is movable in the printing direction by a long stroke of about at least 0.5m (meter) and at most 2 m.

In addition, the inkjet system includes a printhead support for supporting a printhead assembly including at least one printhead for ejecting ink from nozzles toward a substrate.

The ink jet system according to the sixth aspect of the present invention is improved such that: the inkjet system further comprises a support positioning device for positioning the substrate support with respect to the substrate positioning stage in at least one degree of freedom. In particular, the substrate positioning stage can move a short stroke of about at least 0.5mm (millimeters) and at most 10mm, more specifically at least 2mm and at most 8mm, with at least one degree of movement. In particular, the support positioning device is supported by the substrate positioning table.

Advantageously, the positioning of the substrate support relative to the substrate positioning table may compensate for deviations occurring during travel of the substrate positioning table. Such deviations from the theoretically perfect straight-line trajectory of the substrate positioning stage may for example be caused by deviations in the diameter of the stage guide. The occurring deviations can be measured during the travel of the substrate positioning table and subsequently compensated for by the substrate holder being moved relative to the substrate positioning table. Thereby, it is possible to guide the substrate held in the substrate holder more precisely along the longitudinal axis of the inkjet system and to guide it through along the print head.

Due to the fact that the substrate holder can always be properly positioned out of operation in the control and measurement links, the support substrate positioning table itself does not need to be very accurate. This enables low cost designs. For example, a belt drive may be used for driving the substrate positioning table in the printing direction. The substrate support can be actively corrected for all positional errors introduced by the lower arranged substrate positioning stage due to e.g. deviations in the frame and guide diameters.

An orthogonal system including an X-axis, a Y-axis, and a Z-axis may be projected onto the inkjet system. The Y-axis may be defined in a longitudinal direction corresponding to the printing direction. Is defined in the transverse direction as the X-axis. The X-axis extends in a direction transverse to the printing direction. In particular, the X-axis and the Y-axis define a horizontal plane. The Z-axis may be defined in an upward direction. The Z-axis is an up-down axis, and particularly the Z-axis defines a vertical direction. The rotation direction may be defined in relation to the X-axis, the Y-axis and the Z-axis. The tilting motion of the direction Rx of rotation about the X axis can be defined as the rotation of the substrate about a lateral axis. A rolling motion in a rotational direction Ry about the Y-axis may be defined as a rotation of the substrate about the longitudinal axis. The rocking motion of the rotational direction Rz about the Z-axis may be defined as the rotation of the substrate about the up-down axis.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the at least one degree of freedom with which the substrate support is placed coincides with a direction defined by one axis of the orthogonal system. In particular, the substrate support is movable, in particular movable in the printing direction by a stroke of approximately at most 10mm, in particular by a stroke of at most 5mm relative to the substrate positioning table.

In an embodiment of the ink jet system according to the sixth aspect of the invention, a minimum one degree of freedom is managed in the printing direction, wherein the substrate holder is positioned relative to the substrate positioning stage in this degree of freedom. Typically, at least one print head ejects ink drops from nozzles at a constant frequency. To obtain an accurate ink pattern, it may be preferable to pass the substrate along the print head at a constant speed, such that drops are thrown off at regular intervals. The constant speed may be obtained by controlling the substrate holder speed by a master-slave control system, wherein the substrate holder compensates for small speed errors of the travel along the substrate positioning table in the longitudinal direction.

In an embodiment of the inkjet system according to an invention, at least one degree of freedom is managed in an upward direction, wherein the substrate holder is positioned relative to the substrate positioning stage with the degree of freedom. Advantageously, the support positioning apparatus can compensate for deviations in the upward or downward direction during travel of the substrate positioning table.

In an embodiment of the inkjet system according to an invention, the support positioning device positions the substrate support with at least three degrees of freedom. In particular, the support positioning device positions the substrate support in an upward direction (Z-direction), in a rotational direction Ry along a longitudinal axis (Y-axis) and in a rotational direction Rx along a transverse axis (X-axis).

The support positioning device provides for orienting the supported substrate in the substrate support in a virtual plane. In particular, the virtual plane coincides with a plane parallel to the X-Y plane of the orthogonal system lying in a particular horizontal plane. The virtual plane is arranged parallel to an imaginary plane in which the set of nozzles is arranged. By positioning the substrate parallel to the virtual plane, the substrate can be arranged parallel to the imaginary plane formed by the nozzle group. The substrate may be spaced a constant distance from the nozzle group, which enables more accurate positioning of the ink drops on the upper surface of the substrate.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the support positioning device positions the substrate support with all degrees of freedom with respect to the substrate positioning stage. Advantageously, the positioning device provides full control over all possible movements of the substrate. The positioning device allows to compensate for all deviations in all directions of the substrate holder relative to the substrate positioning table.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the support positioning device comprises at least one support actuator, wherein the at least one support actuator positions one degree of freedom in translation. The rest of the five degrees of freedom are left unconstrained while the support actuator defines one degree of freedom. Two mating such holder actuators allow for positioning cooperation with the substrate holder in terms of rotational freedom.

In an embodiment of the ink jet system according to an invention, the support positioning device comprises at least one support actuator and at least one support position measurement system. In particular, the holder actuator is a voice coil actuator. The support position measurement system may be incorporated in the support actuator. The support position measurement system can be built into an encoder with an accuracy of at least 1 micrometer (μm). The support actuator has a support actuator base connectable to the base positioning stage and a support actuator body connectable to the base support. The buttress actuator body is movable relative to the buttress actuator base. In particular, the holder actuator body has a body member that defines a movable direction of only one degree of freedom. In particular, the body member has an elongated portion. Especially the body member is in the shape of an antenna. The body member allows movement in five degrees of freedom, but resists movement (more precisely translation) in a direction parallel to the elongate portion.

In an embodiment of the ink jet system according to the invention the print head holder is stably mounted in the ink jet system. The print head holder is fixed to be connected to a frame of the inkjet system. The print head support may be beam-shaped. As a result, at least one print head is stably mounted in the inkjet system during the printing step of ejecting ink droplets. By moving the substrate holder relative to the stably arranged print head holder, the necessary relative movement of the substrate relative to the print head during the printing step is obtained. Advantageously, the stable mounting of the print head support provides a more accurate ink jet system. No deviations are produced that would occur by moving the print head holder.

In an embodiment of the inkjet system according to the invention, the print head support comprises at least three reference marks. The three reference marks may be incorporated into a print head holder reference surface. The three reference marks define an imaginary plane that is parallel to the imaginary plane formed by the nozzle groups of the print head. In particular, the imaginary plane has a normal vector in the upward direction (Z direction). Advantageously, the substrate support may be aligned by contact with a reference surface of the print head support to align the substrate support to the virtual plane. After the alignment step, also called homing of the substrate holder in the homing position, the holder positioning device is programmed to control the substrate holder parallel to the virtual plane. In particular, during the homing of the substrate support relative to the virtual plane, the support positioning device is programmed with a z-coordinate, a y-coordinate and an x-coordinate to keep the substrate parallel to the virtual plane over an approximately complete printing area, wherein the printing area is determined by the area of the nozzles.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the ink jet system comprises an X calibration element comprising a calibration element X reference surface. The X calibration element is referenced to a surface extending in the printing direction (Y direction) parallel to a plane oriented in the Z and Y axes. The X calibration element is fixedly attached to the frame of the inkjet system. The base support comprises at least two sensors, known as X-sensors, for measuring the relative distance in the X-direction between the base support and the X-reference surface of the calibration element. Preferably, the at least two X sensors are arranged at a predetermined distance (shift) from each other in the Y direction. The at least two X sensors are placed at the same height in the Z direction. Advantageously, the arrangement of the substrate support comprises at least two X sensors, which can be used in the support calibration method according to the sixth aspect of the invention described hereinafter. In particular, at least two X-sensors may be used to provide a more accurate positioning of the substrate support in the X-direction. Advantageously, after the substrate support is repositioned onto the imaginary plane to the repositioned position, the repositioned position of the substrate support can be maintained more accurately during the travel of the substrate positioning stage. In addition, more accurate rotational positioning about the upward axis Rz can be obtained.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the ink jet system comprises a Z calibration element comprising a calibration element Z reference surface. The calibration element is referenced to a surface extending in the printing direction (Y-direction) parallel to a plane oriented in the X-axis and the Y-axis. The Z calibration element is fixedly attached to the frame of the inkjet system. The substrate support comprises at least two sensors, also called Z-sensors, for measuring the relative distance between the substrate support and the Z-reference surface of the calibration element in the Z-direction. The at least two Z sensors are arranged at a predetermined distance (displacement) from each other in the Y direction. The at least two Z-sensors are preferably placed at the same lateral level in the Z-direction. Advantageously, the arrangement of the substrate support comprises at least two sensors, which can be used in the support calibration method according to the sixth aspect of the invention described hereinafter. In particular, at least two Z-sensors may be used to provide a more accurate positioning of the substrate holder in the Z-direction. In particular, the at least two Z-sensors may furthermore be used to provide a more accurate rotational positioning around the transverse axis Rx.

In a further embodiment of the ink jet system according to the sixth aspect of the invention, the ink jet system comprises a Z calibration element comprising a calibration element Z reference surface. The calibration element is referenced to a surface extending in the printing direction (Y-direction) parallel to a plane oriented in the X-axis and the Y-axis. The substrate support comprises at least a third sensor, also called Z3 sensor, for measuring the relative distance in the Z direction between the substrate support and the reference surface of the calibration element Z. The at least third Z3 sensor is arranged at a predetermined distance (shift) in the X direction from at least one other Z sensor. Advantageously, the arrangement of the substrate support comprises at least three sensors, which can be used in the support calibration method according to the sixth aspect of the invention described hereinafter. In particular, the at least three Z-sensors may be used to provide a more accurate positioning of the substrate support in the Z-direction and a more accurate rotational positioning around the longitudinal axis Ry.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the X calibration element and the Z calibration element are combined into one XZ calibration element. Instead of two separate calibration elements, the XZ calibration element advantageously provides one element with a higher functionality. The XZ calibration element includes an X reference surface and a Z reference surface. The XZ calibration element is fixedly attached to the frame of the inkjet system.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the ink jet system comprises a marking unit for marking the substrate by applying at least two fiducial members in a reference surface of the substrate. In particular, the substrate reference surface is the upper surface of the substrate. Further, the inkjet system includes a scanning unit for scanning the reference surface of the substrate to determine the position of the fiducial member. Preferably, the metrology frame supports a scanning unit for scanning the substrate. In particular, the scanning unit is arranged to determine the position of at least two fiducial members in a substrate reference plane of the substrate relative to a scanning reference axis. The scan reference axis has a predetermined orientation in the X-Y plane, for example in the X-direction or the Y-direction.

In an exemplary embodiment of the ink jet system according to the sixth aspect of the invention, the scanning reference axis extends parallel to the ink jet system X-axis. The scanning unit outputs scanned positions of at least two reference members. The scanned position includes a first coordinate in the X direction and a second coordinate in the Y direction. The control electronics of the ink jet system are configured to determine the deviation in the original position of the substrate in the rotational direction Rz about the Z-axis from the at least two scanned positions. The deviation can be compensated for by bringing the substrate into the printing position by a rotational movement of the substrate holder. In the printing position, the substrate is ready to be printed. Further, the control electronics are configured to store the X-calibration values and/or the Y-calibration values to establish X-positions and/or Y-positions, respectively, of the substrate in the printing position.

In an embodiment of the inkjet system according to the sixth aspect of the invention, the inkjet system comprises control electronics comprising software configured to perform the method for calibrating the substrate holder with respect to the virtual plane as described above. The method for calibrating a substrate holder with respect to a virtual plane is performed in an inkjet system.

In an embodiment of the ink jet system according to the sixth aspect of the invention, the ink jet system is a printed circuit board ink jet system, commonly known as a PCB ink jet system. The ink jet system is designed for printing substrates suitable for use as printed circuit boards. The ink jet system is designed to produce printed circuit boards.

Furthermore, a sixth aspect of the invention relates to a method for calibrating a substrate support with respect to a virtual plane. This method is also called a support calibration method. The method comprises at least one step to align at least one degree of freedom of the substrate support with respect to a virtual plane.

Preferably, the substrate is supported by a substrate support during the support calibration method. The support calibration method may be performed for each individual substrate as a preparatory step prior to initiating a printing operation that deposits ink drops onto the substrate. The upper surface of the supported substrate may be used as a substrate reference surface. Advantageously, this may directly result in a varying thickness for the substrate which increases the accuracy of the printing process.

In a method embodiment of performing the steps of the support calibration method, wherein the substrate support is aligned to the print head support. The substrate support is aligned to the print head support by positioning the substrate support, in particular a substrate reference plane of the supported substrate, onto a virtual plane of the print head support at least three spaced points at a constant distance in the Z-direction. This step of alignment may also be referred to as homing of the substrate support. The substrate support may be repositioned to a virtual plane at a separate Y position of the substrate positioning stage. After homing the substrate holder, deviations caused by the substrate positioning device may be compensated by the substrate positioning stage moving the substrate holder along a long stroke of the control holder positioning device to keep the substrate holder positioned in the virtual plane. The deviations introduced by the substrate positioning stage can be calibrated and defined by calibration values used to control the substrate support.

In particular, the constant distance in the Z direction to the virtual plane of the print head support is zero. In one embodiment, the substrate support is aligned by mechanically contacting the substrate support to the print head support. Preferably, the substrate holder contacts the print head holder via the supported substrate at the top of the substrate holder. The substrate holder may be moved in an upward direction until the substrate holder abuts the print head holder. The substrate holder is moved in an upward direction until the print head holder blocks further movement. The base support may be contacted with three reference marks of the print head support. The substrate holder may be brought into contact with a reference surface of the print head holder to align the substrate holder with the print head holder and thus with the virtual plane. After performing this step of the support calibration method, the base support is placed in the Z-direction and in the rotation direction around the X-axis Rx and around the Y-axis Ry. The positioning of the substrate support is read out as a function of the Y position and stored as a calibration value. The calibration values are determined by storing the position values of the support actuators, in particular of the three vertically oriented support actuators, as a function of the Y positioning values of the substrate positioning table.

In an embodiment of the support calibration method, the substrate support may contact the print head support at a plurality of y-positions of the substrate positioning stage to calibrate the substrate support over a range of travel in the printing direction.

In an embodiment of the support calibration method, a further step of the support calibration method is performed, wherein the substrate support is calibrated in a rotational direction Rz about the Z-axis. In the preparation step, the substrate is provided with at least two fiducial members in a reference plane of the substrate. In particular, the reference member is represented by a cross surrounded by at least one circular ring. The marking unit may be used to apply at least two reference points on the substrate. In the support calibration method, the substrate includes at least two reference members supported by a substrate support. The inkjet system includes a scanning unit for scanning the substrate. The scanning unit is mounted to the metrology frame. The scanning unit is arranged in an upper region of the ink jet system beyond the substrate holder, so that the upper surface of the substrate can be scanned. The scanning unit is arranged to determine the position of the at least two reference members relative to the scanning reference axis. In particular, the scan reference axis extends parallel to the inkjet system X axis. The scanning unit outputs scanned positions of at least two reference members. The scanned position includes a first coordinate in the X direction and a second coordinate in the Y direction. The control electronics of the ink jet system are configured to determine a deviation in the position of the substrate in the rotational direction Rz about the Z-axis from the at least two scanned positions. The deviation can be compensated for by a rotational movement of the substrate holder. Further, the control electronics can be configured to store an X calibration value to establish an X position of the substrate. Further, the control electronics can be configured to store an X calibration value to establish an X position of the substrate.

During the travel of the substrate positioning stage, a travel deviation in at least one direction occurs in a desired straight trajectory of the substrate. In an embodiment of the support calibration method according to the sixth aspect of the invention, the ink jet system may be provided with a calibration element, in particular an elongated calibration element, more in particular a calibration strip, to compensate for a travel deviation in the X-direction (so-called X-deviation), or a travel deviation in the Z-direction (so-called Z-deviation). The calibration tape extends in the printing direction (Y direction). The calibration strip is fixedly attached to the frame of the inkjet system. The calibration strip reference is placed parallel to a plane oriented in the Z-axis and Y-axis for measuring the deviation in the X-direction, or parallel to a plane oriented in the X-axis and Y-axis for measuring the deviation in the Z-direction.

In an embodiment of the support calibration method according to the sixth aspect of the invention, the substrate positioning stage moves along the calibration band. In particular, the calibration strip has at least one calibration strip reference surface with a relatively low flatness of about 100 μm with a stroke of about 1.5 meters. This flatness is very low because the substrate needs to be placed in the X-direction with an accuracy of at most 25 μm, especially at most 10 μm, but preferably at most 5 μm.

In one embodiment, the substrate support comprises at least two sensors for measuring the relative distance in the X-direction between the substrate support and the calibration strip reference surface. Preferably, the sensor has a high accuracy of at least 1 μm, in particular at least 0.5 μm, but preferably at least 0.1 μm.

At least one sensor is required to measure the major deviation in the X-direction, which occurs when the substrate positioning table moves along a long stroke. The measured X-deviation is compensated by a movement of the substrate holder in the opposite X-direction.

At least two sensors are required to compensate for the relatively low flatness of the calibration strip. At least two sensors are spaced apart from each other in the Y direction by about a predetermined distance 'S'. The at least two sensors measure the relative distance of the two in the X direction as a function of position along the Y axis of the substrate positioning stage. Thus, the first sensor measures the first relative distance X1 at a particular Y position of the substrate positioning stage and the second sensor measures the second relative distance X2 at the same Y position. The measurement of the relative distance may be performed for approximately the full travel distance of the substrate positioning stage to output a set of X1 values and a set of X2 values as a function of the Y position. The distance 'S' between the first and second sensors is known, which means a shift in the Y direction of the measured X1 and X2 values. By comparing the two sets of measurements X1 and X2 at the first and second Y positions corresponding to a shift at a distance 'S' apart, the flatness of the calibration strip can be determined. The comparison of the two sets of measurements X1 and X2 may be made by subtracting the values X1 and X2 from the corresponding Y position. The flatness of the calibration band may then be taken into account during the controlled movement of the substrate positioning stage. The flatness of the calibration strip and the major X-bias can be compensated in a feed-forward control controlled by the control electronics.

In a similar embodiment, the substrate support comprises at least two sensors for measuring the relative distance in the Z-direction between the substrate support and the calibration strip reference plane. Preferably, the sensor has a high accuracy of at least 1 μm, in particular at least 0.5 μm, but preferably at least 0.1 μm.

At least one sensor is required to measure the major deviation in the Z-direction, which occurs when the substrate positioning table moves along a long stroke. The measured Z-offset is compensated by movement of the substrate holder in the opposite Z-direction.

At least two sensors are required to compensate for the relatively low flatness of the calibration strip. At least two sensors are spaced apart from each other in the Y direction by about a predetermined distance 'S'. The at least two sensors measure the relative distance of the two in the X direction as a function of position along the Y axis of the substrate positioning stage. Thus, the first sensor measures the first relative distance Z1 at a particular Y position of the substrate positioning stage, and the second sensor measures the second relative distance Z2 at the same Y position. This measurement of relative distance may be performed for approximately the full travel distance of the substrate positioning stage to output a set of Z1 values and a set of Z2 values as a function of Y position. The distance 'S' between the first and second sensors is known, which means a shift in the Y direction of the measured Z1 and Z2 values. By comparing the two sets of measurements Z1 and Z2 at the first and second Y positions corresponding to displacements separated by a distance 'S', the flatness of the calibration strip can be determined. The comparison of the two sets of measurements Z1 and Z2 may be made by subtracting the values Z1 and Z2 from the corresponding Y position. The flatness of the calibration band may then be taken into account during the controlled movement of the substrate positioning stage. The flatness of the calibration strip and the major Z deviations can be compensated in a feed forward control controlled by the control electronics.

Furthermore, the invention relates to a method of controlling the position of a substrate support after performing the steps of the support calibration method.

An embodiment according to the sixth aspect of the present invention may be defined by the following 975 prefix terms:

975_1. an ink jet system for printing an ink pattern on a substrate S includes:

a substrate holder for holding a substrate;

a substrate positioning stage PS for positioning the substrate support in the printing direction, wherein the substrate support is supported by the substrate positioning stage, wherein the substrate positioning stage PS is movable by a stage positioning device;

a print head support for supporting a print head assembly comprising at least one print head for ejecting ink from nozzles onto a substrate;

wherein the inkjet system further comprises a support positioning device HD for positioning the substrate support in at least one degree of freedom relative to the substrate positioning stage.

975_2. the ink jet system according to item 975_1, wherein the at least one degree of freedom is managed in a printing direction.

975_3. the ink jet system according to the clause 975_1, wherein the support positioning device HD positions the substrate support SH in at least three degrees of freedom, wherein the substrate support SH is placed in an upward direction (Z direction), in a rotational direction Ry along a longitudinal axis (Y axis) and in a rotational direction Rx along a transverse axis (X axis).

975_4. the ink jet system according to clause 975_1, wherein the support positioning device HD positions the substrate support in all degrees of freedom (X, Y, Z, Rx, Ry, Rz) with respect to the substrate positioning stage.

975_5. an ink jet system according to any of the preceding 975_ clauses, wherein the support positioning device comprises at least one support actuator, wherein the at least one support actuator is positioned in at least one degree of freedom (X, Y, Z) in translation, and wherein two pairs of support actuators together restrict a rotational degree of freedom (Rx, Ry, Rz) in movement.

975_6 an ink jet system according to any of the previous 975_ variants wherein the print head holder H is stably mounted in the ink jet system.

975_7. an ink jet system according to any of the previous 975_ variants wherein the print head holder comprises at least three reference marks Z1, Z2, Z3 defining a virtual plane, wherein the virtual plane is parallel to an imaginary plane formed by the common positioning of a group of nozzles of the print head, in particular the common height in the Z direction, thereby making it possible to place the substrate holder at a constant distance, in particular a zero distance, from the reference marks of the print head holder to align the substrate holder to the print head holder and thus to align the substrate holder to the virtual plane.

975_8 an ink jet system according to clause 975_7, wherein the holder positioning device is programmed to control the substrate holder parallel to the virtual plane.

975_9 an inkjet system according to any of the previous 975_ clauses wherein the inkjet system IS comprises a pressure frame (FF) supporting a Metrology Frame (MF), wherein a Vibration Isolation System (VIS) IS provided between the pressure frame (FF) and the metrology frame MF to support the Metrology Frame (MF) supported by the pressure frame (FF) while isolating the metrology frame MF from vibrations in the pressure frame (FF), wherein the metrology frame MF supports the substrate positioning stage PS and the print head support.

975_10 the inkjet system according to clause 975_9, wherein the stage positioning device comprises a stage guide device, a stage positioning measurement system, and a stage actuator, wherein the stage guide device and the stage positioning device are supported by a metrology frame and wherein the stage actuator is supported by a pressure frame.

975_11 an inkjet system according to any of the clauses 975_6-975_10, wherein the inkjet system comprises at least one Z-sensor (Z) and Control Electronics (CE), wherein the Z-sensor (Z) is stably mounted on a Metrology Frame (MF) for measuring a Z-distance from the associated upper surface for maintaining a constant distance between the virtual plane and the upper surface of the substrate, and the Control Electronics (CE) are configured to receive signals from the at least one Z-sensor (Z) during the printing process, wherein the control electronics are programmed to control the support positioning device HD during a step in the printing process to compensate for a deviation detected by the at least one Z-sensor.

975_12 an inkjet system according to any of the preceding 975_ clauses, wherein the inkjet system comprises a calibration element comprising a calibration element reference surface extending in the direction of the longitudinal axis Y parallel to a plane oriented in the Z-axis and the Y-axis, wherein the substrate support comprises at least two sensors for measuring the relative distance in the X-direction between the substrate support and the calibration element reference surface.

975_13 an ink jet system according to any of the previous 975_ clauses, wherein the ink jet system comprises a marking unit for marking the substrate by applying at least two fiducial members in a reference plane of the substrate.

975_14 the ink jet system according to any of the previous 975_ clauses, wherein the ink jet system further comprises a scanning unit for scanning the substrate, in particular for scanning a reference surface of the substrate to detect the at least two fiducial members.

975_15 an ink jet system according to clause 975_14, wherein the scanning unit is arranged to determine the position of at least two datum members in a substrate reference plane of the substrate relative to a scanning reference axis.

975_16 an inkjet system according to any of the preceding 975_ items, wherein the inkjet system comprises control electronics including software configured to perform the method defined in any of items 17-23 for calibrating a substrate support relative to a virtual plane.

975_17. a method for calibrating a substrate support with respect to a virtual plane in an ink jet system, wherein the virtual plane is parallel to an imaginary plane formed by the positioning of a set of nozzles of a print head placed on a common plane, comprises the step of providing an ink jet system comprising:

a substrate holder for holding a substrate;

a substrate positioning stage PS for positioning the substrate support in the printing direction, wherein the substrate support is supported by the substrate positioning stage, wherein the substrate positioning stage PS is movable by a stage positioning device;

a print head support for supporting a print head assembly comprising at least one print head for ejecting ink from nozzles onto a substrate;

wherein the inkjet system further comprises a support positioning device HD for positioning the substrate support in at least one degree of freedom relative to the substrate positioning stage;

wherein the method comprises at least one of the following steps for calibrating at least one degree of freedom (DOF) of the substrate support relative to the substrate positioning stage:

-aligning the substrate holder to the print head holder by positioning the substrate holder at a constant distance with respect to at least three reference marks Z1, Z2, Z3 of the print head holder defining a virtual plane, wherein the virtual plane is parallel to an imaginary plane formed by the common positioning of a group of nozzles of the print head, in particular the common height in the Z-direction;

-aligning the substrate support by using an X calibration element comprising a calibration element X reference surface extending in the printing direction, i.e. the Y direction, parallel to a plane oriented in the Z axis and the Y axis, wherein the substrate support comprises at least two X sensors for measuring a relative distance in the X direction between the substrate support and the calibration element X reference surface, wherein the at least two X sensors are spaced from each other in the Y direction by about a predetermined shift 'S', performing the calculation by measuring the relative distance in the X direction as a function of a distance travelled by a position along the Y axis of the substrate positioning table relative to at least a part of the substrate positioning table to output a set of X1 values and a set of X2 values as a function of the Y position, wherein the predetermined shift 'S' between the first sensor and the second sensor is used to compare measurements at a first Y position and a second set of Y positions corresponding to the shift 'S', respectively The magnitudes X1 and X2 to determine the flatness of the calibration element to be compensated for during controlled substrate positioning stage movement;

-aligning the substrate support by using a calibration element comprising a calibration element Z reference surface extending in the printing direction (i.e. Y direction) parallel to a plane oriented in the X-axis and the Y-axis, wherein the substrate support comprises at least two Z sensors for measuring a relative distance in the Z direction between the substrate support and the calibration element Z reference surface, wherein the at least two Z sensors are spaced from each other in the Y direction by about a predetermined shift 'S', performing such calculation by measuring the relative distance in the Z direction as a function of a distance travelled by a position along the Y-axis of the substrate positioning stage relative to at least a part of the substrate positioning stage to output a set of Z1 values and a set of Z2 values as a function of the Y position, wherein the predetermined shift 'S' between the first Z sensor and the second Z sensor is used to compare the values at a first Y position and a second Y position corresponding to the shift 'S', respectively Two sets of measurements Z1 and Z2 to determine the flatness of the calibration element to be compensated for during controlled substrate positioning stage movement;

-aligning the substrate holder by using a scanning unit for scanning the substrate, wherein the scanning unit is arranged to determine a rotational offset of at least two fiducial members in the substrate of the substrate supported by the substrate holder with respect to a scanning reference axis, in particular around the Z-axis, wherein the rotational offset will be compensated by a rotational movement of the substrate holder during a controlled movement of the substrate positioning stage.

975_18. the method according to clause 975_17, wherein the substrate is supported by a substrate support during the support calibration method.

975_19. the method according to clauses 975_17 or 975_18, wherein the substrate holder is aligned by mechanically contacting the substrate holder to the print head holder.

975_20. the method according to any of clauses 975_17-975_19, wherein the substrate support is aligned to the virtual plane over a plurality of y-positions of the substrate positioning stage to calibrate the substrate support over a range of travel in the printing direction.

975_21. the method according to any of the clauses 975_17-975_20, wherein the calibration method comprises a preparatory step of providing the substrate with at least two reference members in a reference plane of the substrate.

975_22. the method according to any of the clauses 975_17-975_21, wherein the method further comprises the step of controlling the movement of the ink jet system by control electronics, wherein the control electronics are programmed to compensate for deviations measured during the calibration step.

975_23. a method according to any of the clauses 975_17-975_22, wherein an inkjet system is provided comprising a Z calibration element comprising a calibration element Z reference surface, wherein the calibration element Z reference surface extends in a printing direction (Y-direction) parallel to a plane oriented in an X-axis and a Y-axis, wherein the substrate support comprises at least a third sensor (Z3 sensor) for measuring a relative distance between the substrate support and the calibration element Z reference surface in the Z-direction, wherein the at least third Z3 sensor is arranged at a predetermined distance (shift) in the X-direction from at least one other Z sensor, wherein the method comprises the steps of: by using at least two Z sensors including a Z3 sensor to measure the relative distance in the Z direction and the substrate support is rotated about the longitudinal axis Y axis of the inkjet system relative to the calibration element Z reference plane by an offset Ry and subsequently compensating the position of the substrate support.

A seventh aspect of the invention will now be explained.

A seventh aspect of the invention relates to a substrate conveyor for an inkjet system and a method for conveying a substrate to the substrate conveyor. In particular, the invention relates to the field of printing substrates, such as printed integrated circuits, with high precision. The present invention relates to the field of printing printed circuit boards by using an ink jet system. The substrate conveyor is suitable for use in an inkjet system for printing high precision.

Known ink jet systems for printing substrates include several substrate conveyors for carrying and conveying the substrates. The substrate is supported during the printing operation by a substrate conveyor and is carried by an inkjet system. In some places, it is necessary to transfer substrates from one substrate conveyor to another. Typically, a robot is used to transfer the substrate. The robot includes a suction clamp containing a plurality of suction nozzles to draw the substrate onto the flat upper surface. A robot raises the substrate from the first substrate conveyor to transfer the substrate to the second substrate conveyor.

A first disadvantage of robotic arms is that lifting the substrate leaves a residue of silicone rubber or other contamination on top of the substrate surface. These contaminations interfere with the printing process.

Another disadvantage of the robot is that the accuracy of the transfer is not satisfactory. Positioning the substrate on top of the second substrate conveyor is inaccurate, which leads to dropout and damage in the printing process.

A general object of the present seventh aspect of the invention is to at least partly obviate the above disadvantages and/or provide a usable alternative. In particular, it is an object of the seventh aspect of the invention to provide a transfer unit that efficiently and accurately transfers a supported substrate from a first substrate conveyor to a second substrate conveyor.

According to a seventh aspect of the invention, this object is achieved by the substrate conveyor defined in item 976_ 1.

According to a seventh aspect of the present invention, there is provided a substrate conveyor for supporting and conveying a substrate in an inkjet system. The substrate is moved through the ink jet system in the conveyor direction with the substrate conveyor. The substrate conveyor includes a conveyor body including a conveyor support surface for supporting a substrate. The substrate conveyor comprises a conveyor guide for guiding the conveyor body.

The substrate conveyor further comprises a substrate transfer unit for transferring the substrate to and from the conveyor support surface back to the substrate. The substrate transfer unit includes at least one gripper for gripping the substrate. The substrate transfer unit further includes a clip holder for holding at least one clip and a transfer guide for guiding the clip holder. Further, the transfer unit includes a first supporter actuator for driving the clip supporter along the transfer guide in the transfer direction of the substrate conveyor.

The substrate conveyor according to the seventh aspect of the present invention is improved such that the substrate transfer guide is fixed to the conveyor body so that the substrate transfer guide moves together with the conveyor body during movement of the substrate conveyor body.

Advantageously, the conveying and subsequent positioning of the substrate onto the conveyor support surface can be performed with high precision. Since the transfer guide is fixed to the conveyor body, the substrate can be placed more accurately on the conveyor support surface. Instead of mounting the transfer guide to the frame of the ink jet system, the transfer unit according to the seventh aspect of the invention is mounted directly to the conveyor main body. The transfer unit has a transfer unit reference located on the conveyor, so that a high accuracy of positioning of the transfer unit is possible. The disadvantages caused by the build-up of positioning tolerances during assembly of the inkjet system, which would lead to inaccuracies in the printing method, can be reduced. In addition, more accurate substrate transport reduces damage during operation and improves reliability of the inkjet system.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the at least one clip is movable along the clip path. The clip path extends across the conveyor support surface from a first position to a second position in the direction of the conveyor. The at least one clamp is movable relative to the conveyor body from a first position to a second position. The first location is located at a front region of the substrate conveyor body and the second location is located at a back region of the substrate conveyor body. In operation of the ink jet system, the at least one gripper grips the rectangular substrate at the front or rear side of the rectangular substrate at the edge portion rather than at its lateral edges, as seen in the direction of the conveyor. Whereby the at least one clamp pulls or pushes the substrate onto the conveyor support surface during the transfer operation. Advantageously, the one-sided pull-up or push transfer operation reduces the risk of damage due to bending onto the substrate during the transfer operation, especially when transferring relatively thin substrates. Bilateral lateral bonding can damage thin substrates. Preferably, at least one clamp pulls the substrate onto the conveyor support surface to prevent bending of the substrate during the transfer operation. In order to obtain a pulled transport operation, the at least one gripper of the transport unit grips the substrate on the front or rear edge.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the clip path of the at least one clip is linear and extends through the substrate conveyor in the conveyor direction.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the clip path of the at least one clip comprises a downwardly extending tip. The clip path includes a downwardly extending clip path portion for sinking the clip relative to the base conveyor support surface. As the clip moves along the clip path, the clip moves down to the end of the clip path. Thereby, the clip sinks downward relative to the conveyor support surface. The clips are lowered down below the level of the conveyor support surface so that the substrate can be moved by sliding over the clips.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the at least one clamp comprises a clamping element for clamping the substrate in the edge region. The clamping element comprises a first clamping member and a second clamping member movably connected to each other for clamping an edge of the substrate between the first clamping member and the second clamping member. Advantageously, the clamping element engages over a relatively small area at the edge of the base, which reduces the risk of contamination of the upper surface of the base. Even fine silicon or rubber residue can greatly affect ink flow characteristics during printing operations. In addition, engagement with the clamping element provides a reliable engagement and reduces the risk of damaging the substrate that might otherwise disturb the printing operation.

In an embodiment of the substrate conveyor according to the invention, the clip holder accommodates at least one pair of a first clip and a second clip, wherein the pair of the first clip and the second clip are oriented in opposite directions. Advantageously, the pairs of grippers allow the selective push or pull transfer of the substrate to the other conveyor body.

In an alternative embodiment of the substrate conveyor according to the seventh aspect of the invention, the at least one gripper comprises a suction head for attracting the substrate onto the gripper by means of a suction force.

In an alternative embodiment of the substrate conveyor according to the seventh aspect of the invention, the at least one gripper comprises an electrostatic, magnetic or capacitive head for attracting the substrate to the gripper by an electrostatic, magnetic or capacitive force, respectively.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the clip holders are elongated. The clip support may be beam-shaped. The clip holders extend across the full width of the conveyor body in a transverse direction relative to the conveyor direction. The transfer guide comprises two transfer rails, each of which is mounted on a lateral side of the conveyor body. The clip supports are at the two ends of the linear movable, for example connected to the conveying track by ball bearings. Advantageously, a rigid bearing is thereby provided to obtain precise linear movement of the at least one clip on the conveyor support surface.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the transfer unit comprises a second gripper actuator for moving the clip gripper in an up-down direction. In particular, the clip holder is movable in a substantially vertical direction. Preferably, the second bolster actuator is a voice coil actuator. The transfer unit may further include a clip holder guide for guiding the clip holder in an up-and-down direction. Preferably, the clip support guide is an elastic guide, such as a leaf spring guide, comprising one or two parallel arranged leaf springs. The clip support, in which the at least one clip is positioned, can thus be moved up and down relative to the conveyor support surface to sink the clip support below the level of the conveyor support surface, so that the substrate can pass over the clip support.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the conveyor supporting surface of the conveyor body comprises a plurality of gas openings for holding the substrate in abutting engagement with the conveyor supporting surface by suction or for separating the substrate from the conveyor supporting surface. Preferably, during transport of the substrate, the substrate is attracted to the conveyor support surface by an attraction force, which is generated by attracting gas, in particular air, through the gas openings. In this way it is possible to hold a particularly lightweight substrate in place on top of the conveyor body. When it is necessary to transfer the substrate from the conveyor supporting surface, the suction force can be cancelled and instead of the suction now, the blowing force can be generated by blowing gas, in particular air, into the gas opening of the conveyor body. The substrate is lifted away from the conveyor support surface by the blowing force. Subsequently, a transfer unit is engaged to the substrate to transfer the substrate away from the conveyor body. Advantageously, the gas overpressure allows for contactless substrate transport by the inkjet system.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the conveyor supporting surface of the conveyor body is subdivided into a plurality of engagement areas. The amount of land area can be manipulated according to the apparent size of a particular substrate. Advantageously, the engagement region in the conveyor body allows for processing of substrates in various sizes.

In an embodiment of the substrate conveyor according to the seventh aspect of the invention, the substrate conveyor is arranged as a printing conveyor of an inkjet system for conveying the substrate relative to the print head during a printing operation. The printing conveyor includes a conveyor body that supports the substrate and moves with the substrate during a printing operation.

In a particular embodiment of the printing conveyor according to the seventh aspect of the invention, the conveyor body of the printing conveyor comprises a substrate positioning table for moving the supported substrate in the printing direction relative to the print head holder during the printing operation. Further, the conveyor body of the printing conveyor comprises a table positioning device for positioning the substrate positioning table relative to the frame of the inkjet system. Further, the conveyor body of the printing conveyor includes a substrate holder connected to the substrate positioning table for holding the substrate.

In an embodiment of the printing conveyor according to the seventh aspect of the invention, the substrate transfer unit is connected to the substrate holder. The substrate holder may be movably connected in at least one degree of freedom with respect to the substrate positioning stage. A support positioning device may be provided to position the substrate support in at least one degree of freedom relative to the substrate positioning stage. In particular, the transport guide is fixedly connected to the substrate holder.

In an alternative embodiment of the printing conveyor according to the seventh aspect of the invention, the substrate transfer unit is connected to the substrate positioning table. The transfer guide of the slave transfer unit is fixedly connected to the substrate positioning table. The substrate support is movable in at least one degree of freedom relative to the transport guide.

In an embodiment of the substrate conveyor according to the invention, the substrate conveyor is arranged as a station conveyor for processing substrates. The inkjet system may comprise a station for processing the substrate. The station is, for example, a supply station for supplying the substrate to a printing zone of an inkjet system. The station may be a buffer station for temporarily storing the substrate in the inkjet system. The station may be a discharge station for discharging the substrate after the substrate has been processed in the printing zone of the inkjet system.

Furthermore, the present invention relates to an ink jet system for printing an ink pattern onto a substrate. The ink jet system includes a substrate conveyor as in the embodiments described above. The inkjet system further comprises a frame for supporting elements of the inkjet system and a print head holder for supporting at least one print head, wherein the print head holder is connected to the frame. The substrate conveyor has a conveyor body movable relative to the frame. The substrate transfer unit is connected to the conveyor body such that the substrate transfer unit moves with the conveyor body during movement of the conveyor body.

In an embodiment of the ink jet system according to the seventh aspect of the invention, the ink jet system comprises a substrate conveyor according to the seventh aspect of the invention as a printing conveyor for conveying the substrate in a printing zone during a printing operation.

In an embodiment of the ink jet system according to the seventh aspect of the invention, the ink jet system comprises a processing station for processing the substrate, wherein the processing station comprises a substrate conveyor as the station conveyor for conveying the substrate, wherein the station conveyor comprises a transfer unit arranged to transfer the substrate from the station conveyor to the printing conveyor.

In an embodiment of the ink jet system according to the seventh aspect of the invention, the processing station is a feed station for supplying the substrates to the printing conveyor, a buffer station for temporarily storing the substrates or a discharge station for discharging the substrates out of the printing conveyor.

Furthermore, a seventh aspect of the invention is directed to a method of transferring a substrate from a first substrate conveyor to a second substrate conveyor of an inkjet system. The method comprises the steps of providing a first substrate conveyor and a second substrate conveyor and at least one transfer unit. The at least one transfer unit is connected to at least the first substrate conveyor or the second substrate conveyor. Only one substrate conveyor or both substrate conveyors may be provided with a transfer unit. The transfer unit is mounted to the first substrate conveyor or/and the second substrate conveyor. The transfer unit comprises a clip support comprising at least one clip which is movable along a clip path from a first position in a front area of the substrate conveyor to a second position in a back area of the substrate conveyor.

A method according to a seventh aspect of the invention comprises the step of providing the substrate on a conveyor-supporting surface of a first conveyor. Furthermore, the method according to the invention comprises the step of positioning the second substrate conveyor adjacent to the first substrate conveyor. Depending on the situation, the first substrate conveyor may be placed in front of the second substrate conveyor, or vice versa. According to circumstances, the substrate may be transferred in a forward or backward transfer direction. The substrate may be pulled or pushed onto a second substrate conveyor. The first substrate conveyor and the second substrate conveyor in adjacent positions are aligned relative to their conveyor support surfaces.

The method according to the seventh aspect of the invention comprises the step of positioning the clip support to the first position or the second position, respectively, thereby enabling the at least one clip to clip the substrate at the first conveyor in the edge area. The at least one clip grips the substrate in a small area of the front or rear edge of the substrate. Subsequently, the substrate at the first substrate conveyor is clamped at the edge region. The gripper support is moved to the second position or the first position, respectively, while gripping the substrate and moving the substrate from the first substrate conveyor to the second substrate conveyor. After positioning the substrate on the second substrate conveyor, the substrate is released from the transfer unit.

In an embodiment of the method according to the seventh aspect of the invention, the substrate is transferred from the first substrate conveyor to the second substrate conveyor in a floating state. The floating state is provided by generating a film of gas beneath the supported substrate. The floating state is obtained by supplying gas onto the substrate conveyor support surface below the supported substrate. Advantageously, the substrate is transferred without contacting the substrate conveyor, which reduces the risk of damaging the substrate and reduces the necessary transfer energy.

In an embodiment of the method according to the seventh aspect of the invention, a calibration is performed in the preparation step for positioning the second substrate conveyor adjacent to the first substrate conveyor. The calibration is performed by docking the first substrate conveyor and the second substrate conveyor to each other. The first substrate conveyor is mechanically docked to the second substrate conveyor. A plug and socket arrangement may be provided for mechanically interfacing the first substrate conveyor and the second substrate conveyor. The docking positions of the first and second substrate conveyors may be stored by control electronics of the inkjet system, wherein the first and second substrate conveyors may return to the stored docking positions for conveying the substrates during the printing process. Advantageously, the stored docking position may improve accuracy in the printing process, which may reduce the risk of transport failure or damage to the substrate during transport.

In an embodiment of the method according to the seventh aspect of the invention, the first substrate conveyor or the second substrate conveyor is a printing conveyor, wherein after conveying the substrate onto the printing conveyor, the at least one clip is lowered relative to a conveyor support surface of the printing conveyor. Advantageously, the printing method can be performed without interfering with the transfer unit.

An embodiment according to the seventh aspect of the invention may be defined by the following 976 prefix clause:

976_1. a substrate conveyor for supporting a substrate during movement in an inkjet system, wherein the substrate conveyor comprises a conveyor body comprising a conveyor support surface for supporting the substrate, and a conveyor guide for guiding the conveyor body in a conveyor direction, wherein the substrate conveyor further comprises a substrate transfer unit for transferring the substrate to the conveyor support surface and back from the conveyor support surface to the substrate, wherein the substrate transfer unit comprises

At least one clamp for clamping a substrate;

a clip supporter for supporting the at least one clip;

a transport guide for guiding the clip holder;

a first support actuator for driving the clip support along the transfer guide in a transfer direction along the substrate conveyor;

wherein the substrate transfer guide is fixed to the conveyor body such that the substrate transfer guide moves with the conveyor body during movement of the conveyor body.

976_2. the substrate conveyor according to clause 976_1, wherein the at least one clip is movably supported across the conveyor from a first position to a second position along the clip path, wherein the first position is located at a front region of the body of the substrate conveyor and wherein the second position is located at a back region of the body of the substrate conveyor.

976_3. the base conveyor according to clauses 976_1 or 976_2, wherein the clip path comprises a downwardly extending clip path portion for sinking at least one clip downwardly relative to the base conveyor support surface.

976_4. the substrate conveyor according to any of the clauses 976_1-976_3, wherein the at least one clamp comprises a clamping element for clamping the substrate at the edge region.

976_5. the substrate conveyor according to any of the clauses 976_1-976_3, wherein the clip holder accommodates at least one pair of first and second clips, wherein the pair of first and second clips are oriented in opposite directions.

976_6. the substrate conveyor according to any of clauses 976_1-976_5, wherein the conveyor support surface comprises a plurality of gas openings for holding the substrate in abutting engagement with the conveyor support surface by suction.

976_7. the substrate conveyor according to any of the preceding 976_ clauses, wherein the substrate conveyor is a printing conveyor for transferring substrates during a printing operation, wherein the printing conveyor comprises

A substrate positioning stage for moving the substrate in a printing direction relative to the print head support during a printing operation;

a stage positioning device for positioning the substrate positioning stage relative to the frame; and

a substrate holder connected to the substrate positioning table for holding a substrate;

wherein the substrate holder is movably connected in at least one degree of freedom with respect to the substrate positioning stage. A support positioning device is provided for positioning the substrate support in at least one degree of freedom relative to the substrate positioning stage, wherein the transport guide of the substrate transport unit is fixed to the substrate support.

976_8. the base conveyor according to any one of clauses 976_1-976_6, wherein the base conveyor is a station conveyor of a processing station for processing a base in the processing station.

976 — 9. an ink jet system for printing an ink pattern onto a substrate, comprising a substrate conveyor according to any one of the preceding claims, and further comprising:

a frame for supporting components of the ink jet system;

a print head holder for holding at least one print head, wherein the print head holder is connected to the frame;

wherein the substrate conveyor has a conveyor body movable relative to the frame, wherein the substrate transfer unit is connected to the conveyor body such that the substrate transfer unit moves with the conveyor body during movement of the conveyor body.

976_10 an inkjet system according to item 976_9 includes a substrate conveyor as a printing conveyor for conveying a substrate in a printing zone during a printing operation.

976_11 an inkjet system according to clauses 976_9 or 976_10, wherein the inkjet system comprises a processing station for processing the substrate wherein the processing station comprises a substrate conveyor as a station conveyor for conveying the substrate, wherein the station conveyor comprises a transfer unit arranged to transfer the substrate from the station conveyor to the printing conveyor.

976_12. the ink jet system according to item 976_11, wherein the processing station is a feed station for supplying the substrates to the printing conveyor, a buffer station for temporarily storing the substrates, or a discharge station for discharging the substrates out of the printing conveyor.

976_13. a method of transferring a substrate from a first substrate conveyor to a second substrate conveyor of an inkjet system, comprising the steps of:

-providing a first substrate conveyor and a second substrate conveyor, wherein at least one of the first substrate conveyor and the second substrate conveyor comprises a transfer unit, wherein the transfer unit is mounted to the substrate conveyor, wherein the transfer unit comprises a clip holder comprising at least one clip, which is movable along a clip path from a first position at a front area of the substrate conveyor to a second position at a back area of the substrate conveyor;

-providing a substrate on a conveyor support surface of a first conveyor;

-positioning a second substrate conveyor adjacent to the first substrate conveyor;

-positioning the clip holder to the first position or the second position, respectively, thereby enabling the at least one clip to grip the substrate exiting the first conveyor on the edge region;

-clamping the substrate at the first substrate on the edge region;

-moving the gripper holder to the second position or the first position, respectively, while gripping the substrate and moving the substrate from the first substrate conveyor to the second substrate conveyor; -releasing the substrate when the substrate is placed on the second substrate conveyor.

976_14. the method according to clause 976_13, wherein the substrate is transferred from the first substrate conveyor to the second substrate conveyor in a floating state, the floating state being obtained by supplying gas onto a substrate conveyor supporting surface below the supported substrate.

976_15. the method of clauses 976_13 or 976_14, wherein the position of the substrate on the second substrate conveyor is maintained by an attractive force on the substrate conveyor support surface.

976_16. according to the method of any one of clauses 976_13-976_15, a calibration for positioning the second substrate conveyor adjacent the first substrate conveyor is performed by mechanically docking the first substrate conveyor and the second substrate conveyor to each other, wherein the calibration includes the step of storing the docking position at which the first substrate conveyor is docked to the second substrate conveyor by the control electronics.

976_17. the method according to any of clauses 976_13-976_16, wherein the first substrate conveyor or the second substrate conveyor is a printing conveyor, wherein after conveying the substrate onto the printing conveyor, the at least one clip is lowered relative to a conveyor support surface of the printing conveyor.

Thus, this patent application presents several measures, features and aspects of the invention, where they can be considered as separate inventions or aspects, but these inventions and aspects can be combined in one embodiment to compensate each other and/or enhance the effects that can be obtained. As will be clear from the description herein, the first to seventh aspects of the invention described are considered to be patentable as such and may be subject to separate patent applications. In particular, provisions made specifically for various aspects are considered limitations on patentable subject matter with respect to various aspects of the invention. The claims may be presented for possible divisional application of each individual aspect of the invention.

Several aspects of the present invention will be described in more detail with reference to the accompanying drawings. The drawings show practical embodiments in accordance with any aspect of the present invention and should not be construed to limit the scope of the invention. The measurements described with reference to one aspect of the invention may be combined in advance with the measurements described with reference to another aspect of the invention. Specific features may also be considered as departures from the embodiments shown, and may be viewed in a broad context not only as a delimiting feature from the embodiments shown or aspects, but also as a feature common to all embodiments falling within any aspect of the appended claims and/or the present disclosure, wherein:

with particular reference to the first aspect,

FIG. 1A shows a flow chart of a printing method including a quality check according to a first aspect of the invention;

FIG. 1B shows the flow diagram of FIG. 1A with further refinements of the preparatory steps for extracting control features from a raster input image;

FIG. 2 shows a schematic view of an ink jet system configured to perform the printing method shown in FIG. 1A;

with particular regard to the second aspect in particular,

FIG. 3 depicts an ink jet system according to embodiments of the present invention, in particular embodiments of the second, third and fourth aspects;

FIG. 4 depicts a schematic top view of a printhead assembly of the inkjet system of FIG. 3;

FIG. 5 depicts a schematic view of a print head positioning apparatus according to a second aspect of the present invention suitable for positioning a print head in the ink jet system of FIG. 3;

with particular regard to the third aspect in particular,

FIG. 6 schematically depicts a hot melt ink metering system according to the present invention

FIG. 7 schematically depicts a reservoir of the metering system of FIG. 6 and

FIG. 8 schematically depicts a hot melt ink cartridge according to the present invention

Particularly with respect to the first and second sub-aspects of the fourth aspect,

FIG. 9 depicts a portion of the ink jet system of FIG. 3 and schematically shows a maintenance unit according to an embodiment of the invention;

FIG. 10A depicts in more detail a portion of a maintenance unit according to a first sub-aspect embodiment of the fourth aspect of the present invention suitable for use in the ink jet system of FIG. 3;

fig. 10B depicts in more detail a part of a maintenance unit according to a second sub-aspect embodiment of the fourth aspect of the invention, suitable for use in the ink jet system of fig. 3.

With particular regard to the fifth aspect in particular,

FIG. 11a shows a flow chart of a method according to a fifth aspect of the present invention for printing an ink pattern;

FIG. 11b shows the flowchart of FIG. 11a including an example of a pattern layout;

FIG. 12 shows the classification system in a Cartesian coordinate system;

13 a-13 d show several examples of profile orientations in various directions;

FIG. 14 shows a flow chart in which the contour printing algorithm is subdivided into an overlay algorithm and an ink flow algorithm;

FIG. 15 shows a flow chart of an ink flow algorithm in which a set of overlay elements are converted into an ink pattern;

FIG. 16a shows a combination of overlay elements including a scaled-down effect as an ink flow effect;

FIG. 16b shows the same combination of two overlay elements as shown in FIG. 16a, but by applying another time interval;

FIG. 16c shows an alternative combination of overlay elements to achieve an ink pattern with a particular width; and

fig. 17a and 17b show further exemplary illustrations of two different combinations of test patterns.

With particular regard to the sixth aspect in particular,

FIG. 18 shows, in a schematic view, an ink jet system according to a sixth aspect of the invention;

FIG. 19 shows a cross-sectional view of the ink jet system of FIG. 18;

FIG. 20 shows in detail in a schematic view a printhead assembly spaced vertically from a substrate on a substrate support;

fig. 21 shows in a schematic view the steps of a calibration method for the deliberate determination of the substrate support in the transverse direction; and

fig. 22 shows in schematic view a print head assembly in detail, wherein the print head support is equipped with a Z-sensor provided additionally.

With particular regard to the seventh aspect,

FIG. 23a shows an embodiment of a substrate conveyor according to the invention in a top view;

FIG. 23b shows the substrate conveyor shown in FIG. 23a in a front view;

FIG. 24a shows the transfer unit in a lower position in a side view;

fig. 24b shows the transfer unit in an upper position in a side view;

fig. 25a shows the clip of the transfer unit in perspective view; and

fig. 25b shows the clip of fig. 25a mounted to a transfer unit in a perspective view.

Printed Circuit Boards (PCBs) are used to mechanically support and electrically connect electronic components. The PCB is also called a Printed Wiring Board (PWB) or etched wiring board. Printed circuit boards are used in almost all of the simplest commercially manufactured electronic devices. The PCB includes a substrate containing at least one electrically conductive pathway layer-etched from at least one copper sheet onto a non-conductive substrate. The base has a non-conductive substrate. The substrate typically comprises resin bonded fibers. The substrate is typically formed from a separate layer insulator layered with an epoxy. The board is typically coated with a solder resist mask, which is mostly green in color. The non-conductive substrate is laminated with at least one copper sheet to form a blank PCB, or simply "blank". The blank form is used to manufacture a base product of the PCB.

Printed circuit boards can be manufactured in several ways. In order to manufacture a large-volume PCB and generate a trace or signal trace with a fine line width, it is common practice to manufacture the PCB by a photo-sensing process. In the photosensitive process, a photolithography step using a photomask and developing to selectively remove the photoresist coating is performed. The remaining photoresist protects the copper sheet. Subsequent etching removes unwanted copper. The photomask is typically prepared with a photoplotter using data generated by a technician using a CAM or computer aided manufacturing software.

In this application, the manufacture of printed circuit boards includes the step of printing an anti-etch ink onto a substrate by an ink jet system rather than using a photo-sensitive process. The etch-resistant ink, or simply "corrosion inhibitor", is dropped by the ink jet system onto the surface of the blank. An etch resistant ink is applied over the blank to cover the areas of copper that must be retained during later etching operations. After the resist is applied, the substrate is etched to remove the copper sheet outside the covered area.

Fig. 1A shows a flow schematic sequence of steps for manufacturing a printed circuit board. The manufacture of printed circuit boards is performed by an inkjet system for printing electronic substrates. The inkjet system includes a printhead assembly for ejecting drops of ink onto a substrate and control electronics for controlling the inkjet system. The flow chart shows a first step as an initial step in which the ink jet system receives a pattern layout. The pattern layout defines a desired layout of an ink pattern to be printed on a substrate. The control electronics digitally receive the pattern layout. The pattern layout includes software data. The pattern layout can be submitted to the control electronics by transmission via a network or a data carrier such as a memory stick. The received pattern layout defines a desired layout of the PCB to be generated. The pattern layout may already contain a raster image, but typically the provided pattern layout represents a desired vector image of the PCB. The received pattern layout includes data that can be read or converted by the inkjet system. The pattern layout may be read out and defined as a raster input image by the control electronics of the inkjet system, or read out and converted into a raster input image.

After receiving the pattern layout, a step of rasterizing step R is performed, in which the received pattern layout is read out by the control electronics of the inkjet system, converted or modified into a raster input image "rii". The obtained raster input image "rii" follows the technical input requirements of the inkjet system used in the manufacturing method. The input requirements may depend on specifications of the inkjet system, such as the available nozzle volume and positioning of the printhead assembly. The raster input image is a dot matrix data structure and provides a grid for assigning dot positions. Typically, the grid is a rectangular grid. The raster input image provides a two-dimensional display of the ink pattern in the X-Y plane of the dot locations. The raster image provides a length Y and width X coordinate for each dot of the ink pattern.

In the next third step (printing step P), an ink pattern is printed by dropping ink dots onto the substrate by the print head assembly of the inkjet system. Based on the raster input image, an ink pattern is printed onto the substrate. The printhead assembly is arranged to drop ink droplets onto an upper surface of a substrate and has a plurality of nozzles for ejecting the ink droplets. In an inkjet system, a printhead assembly is disposed beyond a substrate conveyor for transporting substrates. The substrate may be moved under the printhead assembly by driving the substrate conveyor.

In the next fourth step, scanning step S, the printed ink pattern is scanned by a scanning unit of the ink jet system. The scanning unit is arranged to scan the printed ink pattern on the upper surface of the substrate. By scanning the upper surface of the printed substrate, a raster scanned image of the printed ink pattern is obtained. The scanning unit captures a raster-scanned image "rsi" from the ink pattern of the printed substrate.

In the next step Q, a quality check is performed. The quality check is performed by the control electronics of the ink jet system. The queue performs a quality check. Quality checks are performed during the presence of a printed substrate in an inkjet system. In performing the quality check, the printed substrate may stay in the scanning or printing area of the inkjet system. The print zone may be defined as the area in which the substrate moves during the printing operation. The scan area may be located adjacent to the print area. During the quality inspection process, the printed substrate may stay in the buffer zone of the inkjet system. The buffer is incorporated in the ink jet system. The buffer is placed in queue in the ink jet system. The quality check is performed by the control electronics of the ink jet system. In the quality inspection process, the obtained raster scan image "rsi" is compared with the raster input image "rii" and a decision is made to approve or reject the printed substrate. After the quality check, an output signal "os" is provided to indicate further processing of the printed substrate. The first output signal may be indicative of an approved substrate that may be subsequently forwarded to an etching station for etching the substrate. A second output signal may be provided to indicate an unacceptable, non-approved substrate that is subsequently discharged to, for example, a recycle bin.

After performing the embedded quality check, the approved printed substrate is further processed by transporting the printed substrate to a subsequent process station where the inkjet system is located. The next process station may be a subsequent inkjet system for printing the bottom side of the substrate, or an etching station for etching the printed substrate. The substrate may then be transferred to a stripping station for stripping the ink pattern from the substrate to expose the conductive pattern. In a final step, the substrate may be inspected by an automated optical inspection unit. The automated optical inspection may be performed to only check for typical damage to the conductive pattern that has occurred during the etching or stripping process. After final inspection, the substrate may be determined to be approved for use.

After performing the embedded quality check, the rejected printed substrate may be ejected from the inkjet system. The rejected substrate can be discharged to a discharge station D positioned adjacent the ink jet system. The discharge station D may be a recycle station for recycling the rejected substrates or a storage station for storing the rejected substrates. The recycle station may contain a cleaning unit for removing the ink pattern from the rejected substrate. The cleaned substrate may be reused and input into an inkjet system.

FIG. 1B shows a flow chart for a further detailed description of a printing method including an embedded quality check Q. The quality check Q is improved by a preparatory step of extracting at least one control feature "cf" from the raster input image "rii". The control features may define the location or geometry of a particular portion, i.e., the raster input image, that is susceptible to printing faults. The control features may define print areas of the ink pattern in the printing process that have a higher risk of printing faults. In preparation for the quality verification step, features of the raster input image that may promote a higher risk of printing errors are identified.

Fig. 2 depicts an ink jet system for depositing material on a substrate S in a desired ink pattern by ejecting droplets of the material towards the substrate according to an embodiment, in particular, of the first aspect of the invention. The ink jet system is preferably a drop on demand ink jet system that ejects ink drops only when needed. This is in contrast to continuous ink jet systems in which ink drops are continuously ejected at a predetermined frequency and in which the ink drops required to form a pattern are directed toward a substrate and the remaining ink drops are captured, thereby preventing the remaining ink drops from reaching the substrate.

The ink jet system of fig. 2 IS an industrial ink jet system (inkjet system) IS that IS used to deposit a resist material as a mask layer on a printed circuit board, for example, as an alternative to more traditional processes that use photolithographic techniques to provide a mask layer. Because the mask layer can be deposited directly by the inkjet system, the number of processing steps and thus the time for PCB fabrication can be significantly reduced. This application requires high drop placement accuracy and high reliability (per drop calculation).

The ink jet system IS particularly suitable for use in the method according to the invention. The material used is a special ink, also called resist. The ink pattern must be generated according to the available pattern layout. In a first step, the pattern layout is provided to the control electronics CE of the ink jet system.

An orthogonal system including an X-axis, a Y-axis, and a Z-axis may be projected onto the inkjet system.

The Y-axis is the longitudinal axis. The Y-axis may be defined as a direction extending in the printing direction. The print direction of an inkjet system is defined as the direction of movement of the substrate as it passes the print head assembly in order to print a line onto the substrate. The printing direction corresponds to the travel of the substrate positioning table. The travel of the substrate positioning stage corresponds to the maximum stroke of the substrate relative to the printing assembly.

The X-axis may be defined as a direction perpendicular to the Y-axis. The X-axis extends in a direction transverse to the printing direction. The X-axis is the horizontal axis. The X-axis and the Y-axis define a substantially horizontal plane in the inkjet system.

The Z-axis may be defined as a direction perpendicular to the X-axis and the Y-axis. The Z axis extends in an upward direction. The Z axis is the top-down axis. The Z-axis extends in a substantially vertical direction.

The tilting motion of the direction Rx of rotation about the X-axis can be defined as the rotation of the substrate about a lateral axis.

A rolling motion in a rotational direction Ry about the Y-axis may be defined as a rotation of the substrate about the longitudinal axis. The longitudinal axis extends from the front side to the back side of the substrate.

The rocking motion of the rotational direction Rz about the Z-axis may be defined as the rotation of the substrate about the up-down axis.

The ink jet system IS comprises a climate box CB for creating a climate controlled zone around the elements of the ink jet system. The climate box comprises a temperature control device for generating stable climate conditions in the printing process.

To provide a high precision ink jet system, the ink jet system comprises a frame comprising a pressure frame FF supporting a metrology frame MF from a ground surface GR. Between the pressure frame FF and the metrology frame MF, a vibration isolation system is provided to isolate the metrology frame MF from vibrations in the pressure frame FF while supporting the metrology frame MF from the pressure frame FF. As a result, a relatively stable and static printing environment may be generated on the metrology frame that is beneficial to accuracy.

The inkjet system further comprises a print head holder H. Here, the print head holder H is stably installed in the inkjet system. The print head holder H is fixedly connected to the metrology frame MF. The print head support has a beam-like shape. The print head support extends in the X-direction. The print head support bridges the print area PA in which the ink pattern is provided to the surface of the substrate S. The print head holder supports a print head assembly including at least one print head PH. Each print head PH comprises one or more, typically a number of nozzles, from which ink droplets can be ejected towards the substrate S. The printhead assembly defines a printing range in the X direction in which ink drops can be placed during forward or backward rows. The printing range in the X direction defines the width of the printing area PA. The distance between the first and last nozzle in the row of nozzles in the Y direction defines the length of the print area PA.

Further, the inkjet system includes a substrate holder SH that supports the substrate S.

The substrate support SH is movable relative to the print head PH and the scanning unit SU in a printing direction PD parallel to the Y-direction in order to let the substrate S pass under the print head assembly.

In this embodiment, the print head assembly has a print range in the X direction that is at least as large as the largest possible size in the X direction of the substrate that the substrate holder SH can hold. The print head assembly is mounted stable relative to the metrology frame MF.

In the embodiment of fig. 2, the substrate holder SH is supported by a substrate positioning stage PS, which is supported by a metrology frame MF. The substrate positioning stage PS is supported by the metrology frame so that it can move in the printing direction PD, thereby allowing the substrate holder SH to be positioned and hence the substrate S to be positioned in the Y direction. The positioning of the substrate positioning stage is realized using a stage positioning device SD. The stage positioning apparatus includes a stage guide, a stage position measurement system, and a stage actuator.

The table guide is a linear guide. The stage guide means includes a pair of rod-like members for supporting and guiding the substrate positioning stage. The stage guide supports the substrate positioning stage by means of ball bearings. The table guide is connected to the metrology frame MF. Thereby, vibrations from the ground do not hinder the linear guiding of the substrate positioning table.

The stage position measurement system includes a linear encoder. The linear encoder includes an elongated ruler (ruler) extending in the Y direction, and an optical reader mounted to the substrate positioning stage. In operation, the substrate positioning table passes along the ruler to obtain the Y position of the substrate positioning table.

The stage actuator includes a belt and a driving member. The substrate positioning table is connected to a drive element by a belt. The drive element is mounted to the pressure frame FF. The drive element may comprise a gear and a motor. Thereby, a driving force F is applied between the substrate positioning stage PS and the pressure frame FF. As a result, the driving force F does not interfere with the metrology frame MF, but is transmitted to the ground GR via the pressure frame, which results in a higher achievable accuracy of the inkjet system.

Fig. 2 further shows a scanning unit SU for scanning the ink pattern printed on the substrate. The scanning unit SU is fixedly connected to the metrology frame MF. In particular, the scanning unit SU is mounted to the print head support H. The scanning unit SU is placed adjacent to the printing area PA. The scanning unit SU comprises a light source for illuminating at least a part of the ink pattern of the substrate. Further, the scanning unit SU comprises an imaging unit for capturing a scanned image, in particular a raster scanned image. The light source produces illumination of the ink pattern in a particular light color. Preferably, the light source is monochromatic, wherein the color of the light emitted by the light source is tuned to the extreme reflectance values of the ink pattern and/or the background surface.

Control electronics CE are provided to control the ink jet system IS. In particular, the control electronics are arranged to control the position and velocity of the substrate positioning stage. Due to the constant frequency of ejecting the ink droplets, a constant velocity of the substrate positioning stage is required. Variations in the speed of the substrate past the print head can result in gaps in the jetting trajectory.

The control electronics CE are further configured to control the substrate flow in the inkjet system. In the printing method, a stream of the substrate S IS moved through the ink jet system IS. The initial blank substrate S may be provided to the ink jet system IS by a supply station SS, such as a supply conveyor, for supplying blank substrates. The ink jet system IS may have a first buffer unit 1BU at an inlet of the ink jet system for receiving blank substrates from a supply station SS. The first buffer unit 1BU is placed inside the climate box CB. The buffering unit BU provides a buffer area for temporarily storing the substrate S. The first buffering unit 1BU may buffer the substrates received from the supply station, thereby adapting the supplied substrates to a stable condition. After stabilization, the blank substrate is transferred from the first buffer unit 1BU to the substrate holder SH into the printing area PA of the inkjet system for printing the surface of the substrate S. The first damping unit may be a rotation damping unit. The inkjet system IS may have a second buffer unit 2BU for buffering the machine substrate before discharging the printed substrate from the inkjet system IS. The second buffer unit 2BU is placed inside the climate box CB adjacent to the dosing frame MF at the outlet of the ink jet system. The printed substrate may be transferred from the substrate holder SH to the second buffer unit 2 BU. The printed substrate may be buffered in a second buffer unit until the control electronics CE determines whether the substrate can be further processed. In case the control electronics determine that the substrate is approved for further processing, the buffered substrate may be discharged from the inkjet system to the discharge station DS. Alternatively, the buffered substrate may be returned and reentered into the printing area PA to print the backside of the substrate. The discharge station DS may be an etching station that may include a discharge conveyor. In the event that the control electronics determine that the substrate is not approved, the substrate may be discharged into a trash bin. The first and/or second buffer unit may comprise a waste bin B for collecting non-approved substrates from the substrate stream. The collected non-approved substrates may be recycled to obtain blank substrates.

To determine the printed substrate, approved or not, the control electronics CE are configured to perform a quality check Q as illustrated in fig. 1A and 1B. The quality check is performed by the control electronics of the ink jet system. The control electronics CE are configured to receive the pattern layout digitally. The pattern layout defines a desired layout of the ink pattern to be printed on the surface of the substrate S. The control electronics convert the pattern layout into an input image. The input image defines the dot locations of the ink pattern to be printed. The control electronics further receive the scanned image from the scanning unit SU. The control electronics are configured to compare the received scanned image to the input image. Comparison of the scanned and input images determines whether the printed substrate is approved or rejected. After performing the quality check, the control electronics generate output signals for further processing of the substrate.

In addition to the described embodiments, there may be several variations which fall within the scope of protection defined by the appended claims. Instead of a printed circuit board, a printing process may be performed to manufacture other electronic substrates, such as display panels.

It should be noted that the measurements according to the invention and in particular the measurements mentioned in the dependent claims are and are considered patentable as such.

Fig. 3-5 relate in particular to a second aspect of the invention.

Fig. 3 relates in particular to the second, third and fourth aspects according to the invention.

Fig. 3 depicts an inkjet system for depositing an ink fluid in a desired pattern by ejecting droplets DR of the ink fluid in an ejection direction JD toward a substrate S, in accordance with an embodiment of the present invention. The ink jet system is preferably a drop on demand ink jet system that ejects ink drops only when needed. This is in contrast to continuous ink jet systems in which ink drops are continuously ejected at a predetermined frequency and in which the ink drops required to form a pattern are directed toward a substrate and the remaining ink drops are captured, thereby preventing the remaining ink drops from reaching the substrate.

The ink jet system of fig. 3 is an industrial ink jet system that is used to deposit a corrosion resistant material as a mask layer on a Printed Circuit Board (PCB), for example, as an alternative to more traditional processes that use photolithography techniques to provide a mask layer. Because the mask layer can be deposited directly by the inkjet system, the number of processing steps and thus the time for PCB fabrication can be significantly reduced. However, such applications require high drop placement accuracy and high reliability (essentially on a per drop basis).

To provide a highly accurate ink jet system, the ink jet system IS comprises a pressure frame FF supporting a metrology frame MF from a floor GR. Between the pressure frame FF and the metrology frame MF, a Vibration Isolation System (VIS) is provided to isolate the metrology frame MF from vibrations in the pressure frame FF while supporting the metrology frame MF from the pressure frame FF. As a result, a relatively stable and stationary printing environment favorable to accuracy can be generated on the metro frame MF.

The inkjet system further includes a print head assembly having one or more print heads PH supported by a print head holder H and a substrate holder SH supporting a substrate S. Each print head PH of the plurality of print heads PH comprises one or more, typically a number of nozzles, from which ink droplets DR can be ejected towards the substrate S. The nozzles are preferably arranged in an array, i.e. one or more rows. The multiple print heads collectively define a print plane perpendicular to the jetting direction JD that indicates where the substrate must be placed in order to receive jetted ink drops from the multiple print heads.

The substrate support SH can be moved relative to the plurality of print heads PH in a printing direction PD parallel to the Y direction and thus parallel to the printing plane, in order to let the substrate S pass under the print head assembly. In the present application, a distinction is made between moving the substrate holder from left to right, i.e. in the positive Y-direction, while passing the print head assembly, and moving the substrate holder from right to left, i.e. in the negative Y-direction, while passing the print head assembly, in fig. 3. Moving from right to left will be referred to as forward-facing and moving from left to right will be referred to as backward-facing.

Many configurations are possible in order to cover the entire upper surface TS of the substrate S. In the first configuration, the printing plane in this direction is at least as large as the largest possible dimension in the X direction of the substrate S that can be supported by the substrate holder SH. In that case, a single row of the substrate support SH may be sufficient to cover the entire upper surface with ink droplets. In the second configuration, the printing plane in the X direction is smaller than the largest possible size in the X direction of the substrate S that can be supported by the substrate holder SH. In that case, a plurality of parallel rows is required to cover the entire upper surface TS of the substrate S. To allow for multiple parallel rows, the print head assembly and/or the substrate holder SH is movable in the X-direction perpendicular to the printing direction PD.

In case the printing plane in the X-direction is at least as large as the largest possible size in the X-direction of a substrate S that can be supported by the substrate support SH, a plurality of rows may still be required in order to obtain the required printing resolution, since the nozzles in the print head PH may be arranged at a larger distance than the corresponding spacing from each other, for example to prevent or reduce cross-talk (crosstalk) between adjacent nozzles. The substrate is then passed through the print head assembly multiple times, each time moving the substrate in the X direction corresponding to the resolution in order to print the entire pattern.

In this embodiment, the print head assembly has a print plane of a size in the X direction that is at least as large as the largest possible size in the X direction of the substrate that the substrate holder SH can hold. As a result, the print head assembly may be stably mounted relative to the metrology frame MF.

In the embodiment of fig. 3, the substrate holder SH is supported by a substrate positioning stage PS, which is supported by a metrology frame MF. The substrate positioning stage PS is supported by the metrology frame so that it can move in the printing direction PD, thereby allowing the substrate holder SH to be positioned and hence the substrate S to be positioned in the Y direction. Positioning of the substrate positioning stage PS is performed using a stage positioning device SD capable of applying a force between the substrate positioning stage PS and the pressure frame FF. As a result, the force F does not interfere with the metrology frame MF, but is transferred to the ground GR via the pressure frame FF, which results in a higher achievable accuracy of the inkjet system.

Between the substrate positioning stage PS and the substrate support SH, a support positioning device HD is provided for positioning the substrate support SH in one or more degrees of freedom relative to the substrate positioning stage PS, preferably at least in the printing direction PD. With this configuration, the stage positioning device SD can be used to coarsely position the substrate holder SH in the hiss printing direction, while the holder positioning device HD can be used to finely position the substrate holder in the printing direction with respect to the print head assembly. The support positioning device HD can also be used to fine-position the substrate support in other directions, for example in the X-direction and/or in the Z-direction, if desired, and can even fine-position the substrate support in rotational directions such as Rx, Ry and Rz. Preferably, the support positioning device HD is capable of positioning the substrate support in six degrees of freedom relative to the substrate positioning stage.

Positional information about the substrate support SH relative to the metrology frame MF is measured by the measurement system MS. The measuring system is at least configured to measure the position quantification, i.e. the actual position, velocity or acceleration, of the substrate holder in the printing direction PD. In one embodiment, the measurement system measures positional information about the substrate support in six degrees of freedom according to the degree of control applied/required.

The output of the measurement system MS is supplied to the control electronics CE. The control electronics are here depicted as black boxes controlling the overall process in the ink jet system IS. As an example, the output of the measurement system MS may be used to control the electronics drive stage positioning device SD and the support positioning device HD (shown in dashed lines) to accurately position the substrate support relative to the printhead assembly. The control electronics may further send drive signals to the print head PH (see dashed lines) so that the substrate S passes the print head PH while printing the desired pattern on the substrate.

The ink jet system IS further comprises a droplet detection device DD which measures the position of a droplet placed on the substrate, for example by emitting light towards the substrate and detecting the reflected light. The obtained information is also sent to control electronics, which may contain a calibration unit to adjust the position of the print heads relative to each other based on the droplet position information obtained by the droplet detection device. The drop detection device DD can further be used to calibrate the timing of the nozzle firings.

A more detailed description of the various parts of the ink jet system can be found below with reference to the various figures.

Fig. 4 schematically depicts a print head assembly with six print heads 1, 3, 5, 7, 9, 11 as seen from below. The printhead assembly shown may be part of the ink jet system IS shown with respect to fig. 3.

In this embodiment, all print heads are identical. In this embodiment each print head comprises twelve nozzles NO arranged in two rows of six nozzles (see reference numeral print head 7). For simplicity, the nozzles are only shown with respect to the upper print heads 1, 7. The print heads are grouped into groups of three print heads, namely print heads 1, 3, 5 and print heads 7, 9, 11, wherein each group comprises a primary print head 1, 7, an associated secondary print head 3, 9 and an associated tertiary print head 5, 11.

Wherein each nozzle has a virtual printed line on a substrate on which ink fluid drops can be deposited as the substrate is moved relative to the printhead assembly in only the print direction PD. In fig. 4 is depicted a printing line PL1 for a nozzle NO1 of a primary (primary) print head 1.

The secondary and tertiary print heads are arranged at a distance from the associated primary print head in the printing direction. Since the print heads are identical in terms of number of nozzles and nozzle position, each nozzle of the primary print head has a corresponding nozzle at the secondary and tertiary print heads. These corresponding nozzles NO2 and NO3 are shown in fig. 4 for the nozzle NO1 of the primary print head.

The primary, secondary and tertiary print heads are further arranged so that the virtual printed lines PL2 and PL3 of nozzles NO2 and NO3, respectively, are in the same position as the printed line PL1 of nozzle NO 1.

The rows of nozzles NO of each print head are positioned non-perpendicular to the printing direction, i.e. the rows have a non-zero angle α to the direction perpendicular to the printing direction PD. As a result, the distance Δ x between the virtual printed lines of other nozzles can be very small, which means that the resolution can be high, while the distance D between nozzles can be larger to minimize cross-talk between adjacent nozzles without the need for additional print heads as in prior art systems.

Since in this embodiment three nozzles are placed on the same virtual print line, they can advantageously be used to increase the reliability of the system.

In one embodiment, a print performance measurement unit may be provided to measure the print performance of the nozzle, e.g. by looking at the acoustic waves of the actuation cavity connected to the nozzle, which may provide information about the presence of bubbles in the actuation cavity, clogging of the nozzle, etc.

Such a printing performance measuring unit may periodically measure the printing performance of each nozzle. The printing performance of the nozzles may then be compared to the printing performance of the corresponding nozzles within the group. The nozzle with the best printing performance can then be used for printing until another nozzle is measured to have the best printing performance and is used for printing. In this way, the nozzle printing with the best characteristics has been used, which increases the reliability and accuracy of the inkjet system.

The printing performance measuring unit may also be able to predict future printing performance. This allows the following method:

during the backward row BS of the substrate holder, the substrate will first pass the primary print head, then the secondary print head and finally the tertiary print head. In one embodiment, the primary print head and the secondary print head may be used to print in an alternating manner, where each print head prints 10ms, for example. When one of the primary print head or the secondary is not printing, a print performance measurement unit may be used to measure print performance and derive future print performance therefrom. If the printing performance measuring unit, for example, predicts that the nozzle NO1 will not operate satisfactorily for a certain time, the printing with the nozzle NO1 may be stopped and continued with the nozzle NO3 of the third stage print head in order to print alternately with the nozzle NO2 and NO 3.

The printing sequence can be reversed as the substrate holder advances FS, so that under normal conditions the tertiary and secondary print heads print alternately and the primary print head acts as a back-up print head in the event of an imminent nozzle failure.

In the event that two corresponding nozzles fail or operate unsatisfactorily, the third corresponding nozzle may still be used for printing, albeit with an increased risk of error, but again because this nozzle must continue to print. The alarm signal is then preferably transmitted to, for example, a service person.

Fig. 5 schematically depicts a part of a print head positioning apparatus for positioning a print head relative to a print head support in the ink jet system IS of fig. 1. The print head positioning apparatus comprises a base member which in this embodiment comprises two parts BM1 and BM2 which are removably mounted to the print head holder.

Attached to the base member is a body BO having an opening OP for receiving a print head, thereby enabling the body to support the print head. The body is movable in the translation direction TD and the rotation direction RD relative to the base member portions BM1, BM2 by use of elastic hinges H1, H2, H3 and H4.

The print head positioning apparatus may further comprise an actuator to position the body relative to the base member. The actuators are schematically shown by the forces F1 and F2 that can be applied by the actuators. The forces F1 and F2 are shown to have opposite directions, which will result in rotation of the body. By applying forces in the same direction, a translation of the body may be performed. The actuator may for example be a stepper motor.

The connection between the print head holder and the print head is preferably provided at the base member so that further transport of power, data, pressure, etc. from the base member to the print head can take place. As a result, the placement of the unit formed by the print head and the print head positioning device can be done in a plug-and-play manner without having to worry about positioning accuracy.

Fig. 3, 6-8 relate in particular to a third aspect of the invention.

With particular regard to the third aspect of the invention, the ink jet system shown in FIG. 3 further includes an ink metering system for metering ink to the plurality of printheads of the ink jet system. In the embodiment of fig. 3, the ink used is a hot melt ink which has the property that it is a solid material at room temperature and therefore needs to be heated to a high temperature to become a liquid and thus can be jetted. The ink metering system is thus a hot melt ink metering system and is not shown in fig. 3 for simplicity, but is replaced by a schematic diagram in fig. 6. Some print heads PH are also shown in fig. 6 in order to show the connections to the multiple print heads.

Fig. 6 schematically depicts a hot-melt ink metering system 1 for metering hot-melt ink to a plurality of print heads PH according to this embodiment. The hot melt ink metering system 1 of fig. 6 is suitable for use in an ink jet system according to fig. 3.

The metering system 1 comprises a closed circuit comprising a fluid line 3 and in which a reservoir 5 and a pump 7 are arranged. The reservoir 5 is configured to support hot melt ink and the pump 7 is configured to circulate the hot melt ink in a closed circuit in a direction indicated by arrow sign 9.

Hot melt ink has the property that it needs to be heated to high temperatures in order to be able to flow through a closed circuit. The metering system thus includes a heating system configured to heat the hot melt ink to a predetermined operating temperature that allows the hot melt ink to flow in a closed circuit. In this embodiment the heating system comprises a set of heating elements 11, which are able to supply heat to the fluid line and the reservoir. The heating element 11 is shown as a single large component for simplicity, but in practice may be a plurality of heating elements distributed along a closed circuit. The heating element may for example also be incorporated in the pump 7.

The metering system further comprises a fluid connection 13 for each print head PH, wherein the fluid connection is in fluid communication with the closed circuit fluid line 3 to allow the hot melt ink to flow from the closed circuit to the print head PH. In order to control the amount of hot melt ink flowing to the print head PH, a metering valve 15 is provided in each fluid connection.

Due to the fact that hot melt ink circulates in a closed circuit, many print heads can be connected to the closed circuit without significantly affecting the reliability of the metering system. The size of the metering system may be adapted to the consumption rate of the group of printheads connected to the metering system and the desired corresponding refill ratio.

For example, the volume of hot melt ink in the metering system 1 for about sixty printheads PH may be about 2 liters. This has the advantage that the dwell time in the closed circuit is limited and the chance of the hot melt ink changing properties due to ageing is reduced. The small volume also has the advantage that the start-up time, i.e. the time it takes to heat the volume of hot melt ink in the closed circuit to a predetermined operating temperature, is reduced relative to prior art metering systems. Further, the circulation of the hot melt ink has an advantage that a predetermined operating temperature of the hot melt ink can be easily maintained, and by the circulation, disturbances (e.g., thermal disturbances) at a specific place in the closed circuit are averaged in principle over the closed circuit, and can be easily compensated for at another place of the closed circuit. This is also advantageous from a reliability point of view.

To measure the amount of hot melt ink in the closed circuit, the reservoir includes a level sensor 17. It may be desirable to have the amount of hot melt ink in the closed circuit above a predetermined minimum level so that sufficient hot melt ink can be ensured for the print head. The level sensor is therefore preferably configured to detect whether the level of the hot melt ink is below or above a predetermined minimum level.

The level sensor 17 of fig. 6 comprises a tubular metering slot 19 having an open end 21 at the bottom of the tubular metering slot 19 which can be closed by hot melt ink if the level of hot melt ink in the reservoir is above the level of the open end 21. The metering tank 19 is connected to an air volume displacement device 23 configured to supply a predetermined volume of air into the metering tank 19. In this embodiment, the air volume displacement device 23 is a movable piston 25 in a cylinder 27. Air is moved into and out of metering slot 19 by moving piston 25 up and down within cylinder 27.

The level sensor further comprises a pressure sensor 29 to measure the pressure difference between the air pressure in the metering tank 19 and the air pressure in the reservoir above the hot melt ink. In this embodiment, the pressure sensor 29 is connected to the reservoir via a cylindrical member 31 extending in the reservoir, said cylindrical member 31 being in fluid communication with the interior of the reservoir via an open end 33.

In the reservoir, three possible levels of hot melt ink are shown, namely a low level 35, a high level 37 and an intermediate level 39. When the level of hot melt ink in the reservoir is, for example, at the low level 35, the metering slot 19 is in fluid communication with the barrel member 31 so that supplying air to the metering slot 19 using the air volume displacing device 23 will not result in a pressure differential between the air pressure in the metering slot 19 and the air pressure in the barrel member 31. When the liquid level rises above the open end 21 of the metering tank 19, for example to an intermediate liquid level 39 or a high liquid level 37, the metering tank 19 is closed by the hot melt ink and is no longer in fluid communication with the cylindrical member 31. If air is now introduced into the metering slot 19, the air pressure inside the metering slot 19 will increase relative to the air pressure inside the cylindrical member 31. Thus, the air pressure differential, which is favorable to the air pressure in the metering slot 19, indicates whether the level of hot melt ink in the reservoir is above or below the level corresponding to the height at which the open end 21 of the metering slot 19 is located.

The liquid level inside the reservoir can also be measured at regular intervals by moving the piston 25 up and down periodically. Other options for the air volume displacement device are also conceivable.

The level sensor of fig. 6 further comprises a tubular metering slot 41 having an open end 43 at the bottom of the tubular metering slot 41, said open end 43 being closable by hot melt ink if the level of hot melt ink in the reservoir is above the level of the open end 43. The metering tank 41 is connected to an air volume displacement device 45 configured to supply a predetermined volume of air into the metering tank 41. In this embodiment, the air volume displacing device 23, 45 is for example a movable piston 47 in a cylinder 49. Air is moved into and out of metering slot 41 by moving piston 47 up and down within cylinder 49.

The level sensor further comprises a pressure sensor 51 to measure the pressure difference between the air pressure in the metering tank 41 and the air pressure in the reservoir above the hot melt ink, in this embodiment via a connection between the pressure sensor 51 and the cylindrical member 31. When the level of hot melt ink inside the reservoir is below the open end 43, for example at the intermediate level 39 or the low level 35, supplying air to the metering slot 41 using the air volume displacement device 45 will not result in a pressure differential between the air pressure in the metering slot 41 and the air pressure in the cylindrical member 31. When the liquid surface rises above the open end 43 of the metering slot 41, for example to the high liquid surface 37, the metering slot 41 is closed by the hot melt ink and the metering slot 41 is no longer in fluid communication with the cylindrical member 31. If air is now introduced into the metering slot 41, the air pressure inside the metering slot 41 will increase relative to the air pressure inside the cylindrical member 31. Thus, the air pressure differential, which is favorable to the air pressure in the metering slot 41, indicates whether the level of hot melt ink in the reservoir is above or below the level corresponding to the height at which the open end 43 of the metering slot 41 is located.

By moving the piston 47 up and down periodically, the liquid level in the reservoir can also be measured at regular time intervals. Other options for the air volume displacement device are also conceivable.

Thus, metering slot 19 may be used to indicate a low level inside the reservoir and metering slot 41 may be used to indicate a high level inside the reservoir, so that the control system can maintain the level of hot melt ink in the reservoir substantially between these two levels to ensure that sufficient hot melt ink is available to the printhead PH while the amount of hot melt ink is maintained below a predetermined maximum to avoid unnecessary heat loading of the hot melt ink, thereby reducing the chance of aging.

The hot melt ink tank 53 may be connected to a reservoir. The hot-melt ink tank 53 is in the connected state shown in fig. 6, but may be separated if necessary, so that an empty hot-melt ink tank can be replaced with a filled hot-melt ink tank.

The hot melt ink cartridge includes solid hot melt ink 54 in a filled state. The heating system of the metering system includes a heating element 55 capable of applying heat to the cartridge to melt the hot melt ink when the cartridge is connected to the reservoir, which allows the hot melt ink to flow into the reservoir to replenish the hot melt ink in the closed circuit.

In this embodiment, the hot melt ink cartridge allows the hot melt ink to be melted only when needed by the metering system. Thus, when the liquid level in the reservoir drops below the predetermined minimum level set by the metering slot 19, the heating element 55 may be operated to melt the hot melt ink in the cartridge until the liquid level has been sufficiently raised. The reservoir may not be refilled until the level at which the metering slot 41 is located is reached, but the cartridge may also be sized to be an intermediate level obtained when the cartridge is emptied, such that the highest level may be present for safety reasons only, or may be omitted.

The reservoir in the embodiment of fig. 6 comprises a siphon 57 to which the cartridge is connectable. The siphon ensures that there is a gas separation between the interior of the reservoir and the environment when the cartridge is removed from the reservoir, which provides a safe working situation. The heating system may further comprise a heating element 59 to melt the solidified hot melt in the siphon tube if necessary.

When the cartridge is connected to the reservoir, it comprises a bottom opening 58, through which bottom opening 58 the melted ink can flow towards the siphon 57. Due to the fact that the hot melt ink is present inside the ink cartridge in a solid and liquid phase, it is very likely that a vacuum formed inside the cartridge prevents the ink from flowing out of the cartridge if no measurement is taken. In the embodiment of fig. 6, this is prevented by providing a spacer 56 over the opening 58, wherein the spacer has at least as large a surface area as the opening to completely cover the opening, and wherein the spacer is arranged between the internal solid hot melt 54 of the cartridge and the opening, such that the melted ink must flow around the spacer to reach the opening.

Fig. 7 depicts a cross-sectional view of the reservoir 5 according to an embodiment of the invention. The cross-section of the reservoir has a U-shape, thus providing a large surface area to volume ratio of the reservoir 5. As a result, the maximum distance inside the reservoir and the closest wall of the reservoir are both limited so that the hot-melt ink is heated relatively quickly when heat is applied to the interior of the reservoir through the wall. The U-shape is advantageous in that the overall size of the reservoir is within certain limits.

FIG. 8 depicts a cross-sectional view of a hot melt ink tank 53 according to an embodiment of the present invention. The cartridge is a container having at least one opening 58 connectable to the reservoir. The cartridge is oriented with the open front facing down so that ink can flow out of the cartridge due to gravity. The opening may be closed by a movable closure member when the cartridge is not connected to the reservoir.

A spacer 56 is provided inside the cartridge at a distance from the opening and the opening between the solid hot melt ink. As a result, the melted ink must flow around the spacer toward the opening 58 as indicated by the arrow mark AR. In order to correctly position the spacers inside the box, the spacers may be equipped with projections 56A extending sideways from the spacers towards the side walls of the box. Ink can then flow between the protrusions towards the openings. To keep the spacers at a distance from the opening, the spacers may include an extension 58B, which may be formed by a ridge. The extension 58B and the protrusion 58A may also be used as a heat conductor so that heat applied to the lower portion of the cartridge to melt the hot melt ink is also conducted to the spacer via the extension 58B and the protrusion 58A.

Fig. 3, 9-10B relate in particular to a fourth aspect of the invention.

The ink jet system as shown in fig. 3 further comprises a maintenance unit MU (see fig. 9) configured to remove ink fluid from the surface SU of the print head PH on which the nozzles are arranged, since during the printing process ink fluid may accumulate on said surface, which reduces the achievable accuracy and reliability.

Referring to fig. 9, the surface SU of the print head PH is shown, wherein the print head assembly is shown from below. The printing direction PD is also indicated by a respective arrow to indicate the transport direction of the substrate for printing. For the sake of clarity, only some print heads and some SUs are indicated by the respective reference numerals PH and SU.

Fig. 9 also shows schematically a wiper frame WSF of the maintenance unit MU, which can be moved between the inoperative position NOP shown in fig. 9, in which maintenance cannot be performed on the print head and a maintenance position MP below the print head (see dashed box), in which maintenance action can be performed on the print head by the maintenance unit. For this purpose, guide means G1, G2 are provided, along which the wiper frame can be moved between the inoperative position and the maintenance position. The movement of the wiper frame may be caused by respective actuation systems provided between the wiper frame and the guides G1, G2.

The inoperative position of the wiper frame in this case abuts the transport area of the substrate, i.e. the movability of the wiper frame is in a direction D1 perpendicular to the printing direction PD, which has the advantage that the maintenance unit can be moved to a position in which the maintenance unit does not interfere with the printing activity (i.e. does not interfere with passing through the substrate or the substrate holder).

The maintenance unit MU further comprises a plurality of wipers with respective wiper moving devices to move the wipers in direction D2 relative to the wiper frame WSF. The direction D2 is in this embodiment parallel to the longitudinal direction of the surface SU of the print head PH. The dashed box W schematically indicates the wiper and the wiper moving device operable on the other side of the wiper frame, i.e. the side of the wiper frame facing the print head surface when in the maintenance position MP.

This configuration allows the wiper frame to be placed in direction D1 such that the wiper is aligned with the first column surface SU of the print head, after which the wiper is subsequently moved along the surface of the print head by the wiper positioning device. After the wiping action is performed, the wiper may be properly positioned relative to the second column of print heads for the next wiping action, and so on until all of the print heads of the print head assembly are wiped clean. In this case, the wiper frame is moved stepwise and the wiping action is performed by the wiper moving device while keeping the wiper frame stable with respect to the print head assembly. It is obvious to a person skilled in the art of maintenance units for ink jet systems that other structures for moving the wiper can also be envisaged.

Hereto, the maintenance unit may be according to the first or second sub-aspect of the fourth aspect of the invention. An example of a maintenance unit according to the first sub-aspect of the fourth aspect of the invention will be given with reference to fig. 10A and an example of a maintenance unit according to the second sub-aspect of the invention will be given with reference to fig. 10B.

Fig. 10A schematically depicts a part of a maintenance unit MU according to an embodiment of the first sub-aspect of the invention, which maintenance unit MU can be used in the ink jet system of fig. 3 and 9. Shown is a wiper frame WSF that movably supports a frame FR. Between the frame FR and the wiper frame WSF, the wiper mobile device WMD is operable to generate a pressure F1 to position the frame FR relative to the wiper frame WSF.

Arranged on the frame FR is a wiper W1, which is moved along the print head surface. The wiper W1 is guided in its movement by a guide having two parallel spring blades LF which together form a linear guide allowing the wiper to move only up and down. Attached to the wiper W1 is a permanent magnet PM that is part of the piezo actuator. The permanent magnet is arranged inside a coil CO, which is another part of the piezo actuator, so that by supplying an electric current to the coil by means of a suitable energy source, such as a power supply, a pressure will be generated on the permanent magnet due to the interaction between the respective magnetic fields of the magnet and the coil. This pressure may be used to position the wiper relative to the surface SU of the print head PH, which is shown in dashed lines, in a direction perpendicular to the surface SU of the print head PH.

The position of the wiper W1 relative to the surface SU is indirectly measured using the position sensor PS on the assumption that the distance between the frame FR and the surface SU is substantially the same each time. The output of the position sensor is sent to a controller CON which provides a drive signal to the power source CS to apply a current I to the piezo actuator and the wiper moving device WMD based on the output of the position sensor. In order to provide a predetermined wiping force to the surface SU, the maintenance unit comprises a set point generator SG providing a set point corresponding to the location of the wiper W1 inside the print head PH, as shown by wiper W1'. However, the wiper W1 cannot reach that point, so that the controller will continue to push the wiper W1 toward the position W1' using the force actuator. The controller comprises a limiter LI which keeps the maximum applicable force applied by the force actuator within a predetermined value, in this embodiment by limiting the maximum current that can be generated by the power supply. The result is that substantially the same wiping force is applied to the wiper independent of changes in the characteristics of the wiper.

Fig. 10B schematically depicts a part of a maintenance unit MU according to an embodiment of the second sub-aspect of the fourth aspect of the invention, which maintenance unit MU can be used in the ink jet system of fig. 3 and 9. Shown is a wiper frame WSF that movably supports a frame FR. Between the frame FR and the wiper frame WSF, the wiper mobile device WMD is operable to generate a pressure F1 to position the frame FR relative to the wiper frame WSF.

Arranged on the frame FR is a wiper W1, which is moved along the print head surface. The wiper W1 is guided in its movement by a guide having two parallel spring blades LF which together form a linear guide allowing the wiper to move only up and down. Attached to the wiper W1 is a permanent magnet PM that is part of the piezo actuator. The permanent magnet is arranged inside a coil CO, which is another part of the piezo actuator, so that by means of a suitable energy source, such as a power supply, a current I is supplied to the coil, which will create a pressure on the permanent magnet due to the interaction of the magnet and the coil. This force can be used to press the wiper against the surface of the print head during the wiping action.

Preferably, the force actuator is configured such that a substantially constant current versus force relationship is obtained over the working range of the wiper. This allows for an open loop type of control where the appropriate control current controls the force applied to the wiper by the force actuator through the coil. The current may be measured using a measurement resistor R1 and a voltage V1 across the measurement resistor R1. The measured current may be provided to a controller CON, which is capable of controlling the power supply CS based on said measured current.

In the case where the leaf spring of the guide device does not apply a significant force to the wiper while guiding the wiper within its working range, the force applied by the force actuator corresponds to the wiper force with which the wiper is pressed onto the surface of the print head, independently of the stiffness of the wiper, the actual position of the wiper, etc. In some embodiments, it may be necessary to overcome a known or determinable constant force, such as gravity, but such a constant force can be easily compensated for.

In the case where the force applied to the wiper by the guide means is significant and non-constant, or when the current-force relationship is not constant, the open loop control may not be sufficient. In general, the current-force relationship depends on the position of the permanent magnet inside the coil, so adding a position sensor PS for determining the position of the magnet may be beneficial for accurately determining the force applied to the wiper by the force actuator.

The position sensor PS may alternatively or additionally be used to determine the position of the guiding device. In the case where the rigidity of the spring plate is excessively high in the vertical direction, the disturbing force applied to the wiper by the guide means also depends on the position of the wiper with respect to the guide means. Thus, measuring the position allows the disturbance force of the guiding device to be determined, which can be compensated when it is sent to the controller.

Fig. 11-17 relate in particular to a fifth aspect of the invention.

Fig. 11a shows a flow chart of a method according to the invention. In this method, the control electronics of the inkjet system receive a pattern layout L. The control electronics contain software to convert the pattern layout into an ink pattern. The software contains logic L that converts the received pattern layout L into a separate outline layer comprising at least one outline portion and a separate inner area layer comprising at least one inner area portion of the pattern layout. The logic L provides output data that is used to control at least one printhead of the inkjet system. Logic L provides a first 1 output data and a second 2 output data. The first output data 1 comprises contour data for printing a contour defined in a contour layer. The second output data 2 comprises inner region data for printing an inner region defined by the inner region layer. The outline region of the pattern layout defines an outline of the pattern layout. An area surrounded by at least two bounding areas defines an inner area. The contour form is used for the boundary of the inner region. The first and second output data are then processed to print an ink pattern. In a first step, the profile data is processed to print the profile. The contour C is printed by depositing contour ink droplets onto the substrate. In a second subsequent step, the inner region data is processed to print the inner region inside the printed outline. The inner area F is printed by depositing a filler ink droplet on the substrate. After printing both the contour C and the inner area F, the final ink pattern P is obtained.

Fig. 11b illustrates processing of an exemplary pattern layout in the flowchart illustrated in fig. 11 a. The pattern layout is typically an Integrated Circuit (IC) pattern layout and includes circuit lines and a tail of a circle. The rounded tail of the IC pattern layout may be used to connect electrical components to form a Printed Circuit Board (PCB). In the method according to the invention, the IC pattern layout P is divided into a profile layer and an inner zone layer. Applying logic l to the IC pattern layout and generating profile data 1, the profile data 1 is first processed to print a profile C on the substrate. The obtained contour C is depicted in the subsequent block in the flow chart of fig. 11 b. Contour C is a contour outline of the pattern layout. Logic l is further applied to generate the inner region data 2. The inner region data 2 is processed to print an inner region F on the substrate. The inner area F can be printed by printing at least one row of infill drops inside the already printed outline. The inner region F may be defined as subtracting the pattern layout defining the outer edge of the contour. The outer edge may have a width of at least one contour drop. Preferably, the outer edge has a width of one contour droplet.

The control electronics contain a contour printing algorithm to print the contour C onto the substrate. The contour printing algorithm converts the contour into a set of contour drop positions.

The contour printing algorithm is, for example, a rasterization algorithm, wherein contour data is projected onto a raster to obtain a distribution of contour ink drops. The grating may have a plurality of grating elements, wherein the contour algorithm may generate drop positions for each grating element covered by a certain amount.

Preferably, the contour printing algorithm is based on the orientation of at least a part of the contour. The orientation of at least a portion of the profile is measured relative to a reference axis. Orientation may be defined by an angle relative to a reference axis. In the step of the orientation-based contour printing algorithm, at least a part of the contours is classified depending on the defined orientation. At least a portion of the contours are classified in a category of a classification system. Each category has its own transformation to obtain the placement of a set of outline drops. The transformation of the contours is different depending on the orientation of at least a portion of the contours. Thereby, an optimal compensation of the interaction mechanism between adjacent ink droplets can be achieved. The contour drops are printed by applying a contour printing algorithm that depends on the selection of the category.

The classification system is depicted in fig. 12 in a cartesian coordinate system. The cartesian coordinate system has a first quadrant bounded by an X-axis and a Y-axis. The classification system has three classes, a first class I, a second class II and a third class III.

A first category I is defined for a set of contour portions having an orientation in the X-axis direction and below an angle larger than the predetermined angle alpha. The predetermined angle α is an angle in the first quadrant with respect to the Y-axis. The predetermined angle α may be a parameter that may be a function of ink flow and/or substrate characteristics.

A second category II is defined for a set of contour parts oriented in a direction that is small or equal to or below the predetermined angle alpha.

A third category III is defined for having a set of contour portions oriented in the Y-axis direction.

In the method according to the invention, a cartesian coordinate system is projected onto the layout of the ink jet system. The inkjet system has a layout that includes a print direction corresponding to a direction of travel of the substrate. The Y-axis is projected into the printing direction of the inkjet system.

According to the method of the invention, all the divided contour parts are divided into one of three categories. The contour portion oriented to fall outside the first quadrant and one of the second, third or fourth quadrants of the cartesian coordinate system is first mirrored in a preparation step to obtain the orientation falling in the first quadrant. In a subsequent step, a set of drop positions is determined, wherein the mirror image step is again compensated to obtain a set of drop positions in the corresponding quadrant.

Fig. 13 a-13 d show several examples of profile orientations in various directions. The outline may be combined into a plurality of outline portions to obtain a complete outline as defined by the pattern layout. The figures show the X-axis and Y-axis of a cartesian coordinate system. The ink pattern is shown with a contour C and an inner area F. The ink pattern is obtained by depositing contours and filling ink drops in a printing process. The printing direction is parallel to the Y-axis. The profile C is deposited first and formed from an array of profiled ink drops. The outline ink drops of the array form a strip element. The inner region is formed by depositing filler ink droplets to fill the area between the two opposing contours C. Fill drops are deposited in rows. 13 a-13 d show a bold line C \ at outline C indicating the resulting pattern layout edge demarcating the ink pattern after drooling.

Fig. 13a shows the orientation of the contours in the first category I. The orientation of the contour is in the X-direction. The profile is formed by depositing a profile ink drop. The outline drops are placed in a line and have a constant Y coordinate. The outline ink drops form a strip element. The strip elements are formed with contour ink drops of constant size. A single array of outline ink drops is used to form the strip elements. The strip-like elements have a constant pitch. The mutual distance between two consecutive contour drops in a strip-shaped element is constant.

Fig. 13b shows another orientation of the profile in the first category I, wherein the orientation is below an angle greater than or equal to the predetermined angle a with respect to the Y-axis. The profile is formed by depositing a profile ink drop. The outline ink drops are placed in a line. The outline ink drops form a strip element. The strip elements are formed with two arrays of outline ink drops. The strip elements are formed with contour ink drops of constant size. The strip-like elements have a constant pitch. The mutual distance between two consecutive contour drops in a strip-shaped element is constant.

Fig. 13c shows the orientation of the contours in the second category II. The orientation of the profile is in a direction below an angle smaller than the predetermined angle alpha with respect to the Y-axis, as shown in fig. 13 b. The profile is formed by depositing a profile ink drop. The outline ink drops form a strip element. The strip elements are formed from a single outer array of outline ink drops. The strip elements have varying spacing between the ink drops. The mutual distance between two consecutive contour drops in a strip-shaped element increases linearly in the Y-direction of the contour element. The mutual distance between a pair of two adjacent drops is a function of the position of a pair of drops. The strip elements are formed with contour ink drops of constant size.

The band elements are formed by band-split sequences. The band split extends in the Y direction. Each band split has a constant X coordinate. Each band is divided into fixed lengths having fixed amounts of ink droplets to obtain bands having a linear extension in the pitch orientation. Adjacent swathes in the X direction are interleaved with drops of the interleaved pitch size. Initially, the initial outer edge has an edge notch in a cross section from the first line in the Y direction to the second line in the Y direction, as indicated by the bold line C \ compared to the resulting ink pattern. After the ink drop is discharged, the outer edge of the result indicated by the thick line "C" is obtained.

Fig. 13d shows the orientation of the contours in the third category III. The orientation of the contour is in the Y direction. The profile is formed by depositing a profile ink drop. The outline drops are placed in a line and have a constant X coordinate. The outline ink drops form a strip element. The strip elements are formed with contour ink drops of constant size. A single array of outline ink drops is used to form the strip elements. The strip-like elements have a constant pitch. The mutual distance between two consecutive contour drops in a strip-shaped element is constant.

FIG. 13d further illustrates the effect of changing ink flow when adjusting the pitch of the strip elements. The bold line C marks the outer edge of the resulting ink pattern. In this illustration, the left side applies a smaller pitch between drops than the front side. On the front side of the illustration, the deposited ink drops have almost no ink flow over a predetermined time interval, the outer edge of the contour coinciding with the bold line C. In contrast, the left side of the illustration shows that by applying a small pitch, relatively more ink flow occurs in the time interval. By applying a small pitch, an initial offset occurs, wherein the outer edge of the contour is located away from the edge of the finally obtained pattern layout, as indicated by the thick line C.

Fig. 14 shows a flow chart in which the contour printing algorithm CPA is subdivided into an overlay algorithm CA and an ink flow algorithm IFA. In a first step the overlay algorithm CA is applied. In the second step, the ink flow algorithm IFA is applied.

The pattern layout L is an input for the overlay algorithm CA. In the overlay algorithm, the outline, outline portion, of at least a portion of the pattern layout is converted into a set of overlay elements. The pattern layout is composed by overlay elements. Overlay algorithms are used to obtain the best overlay of the pattern layout by the overlay elements. The set of overlay elements, including overlay element positions, are the output after applying an overlay algorithm to the pattern layout. In particular, the cover element is a strip element. The strip-shaped elements as covering elements contain the length, orientation and at least one absolute position of the ink drop. The set of overlay elements may be printed in a subsequent step to obtain the ink pattern P.

The overlay algorithm may include several overlay parameters for defining overlay elements. The overlay parameter may be a function or value of the droplet size, the number of droplets per overlay element, the mutual distance between two adjacent droplets in an overlay element. The overlay parameters may be varied depending on, for example, the ink and substrate material.

The ink flow algorithm converts the overlay elements into a set of absolute positions for the outline ink drops to obtain an ink pattern that includes factors for the ink flow behavior. The overlay element is an input for the ink flow algorithm. A set of absolute positions of the ink drops is the output of the ink flow algorithm. In particular, a bitmap can be generated that contains the positions of the ink drops for the most ideal print coverage element. Control electronics are provided to translate the set of absolute positions of the ink pattern into control signals for the inkjet system, and in particular for the print head and substrate positioning stage.

FIG. 15 shows a flow chart of an ink flow algorithm in which a set of overlay elements is converted into an ink pattern P.

The ink flow algorithm has ink flow parameters determined by using an inkjet system. The ink flow parameter is determined in several steps. In a first step 5.1, at least one test pattern is printed. Preferably, the test pattern is an overlay element or a set of overlay elements. In a second step 5.2, at least one test pattern is scanned. The inkjet system has a scanning unit for scanning the test pattern. An image of the test pattern is captured by the scanning unit. The scanning unit is an internal scanning unit. The scanning unit is incorporated in an ink jet system. In a third step 5.3, the test pattern is extracted. In a fourth step 5.4 at least one relevant parameter, e.g. width, is extracted from the test pattern. Thus, measurement data is collected to establish ink flow effects. In a fifth step 5.5, the ink flow parameters are determined. The measurement data may be compared to the pattern layout to determine any deficiencies. For example, the width of the test pattern may be compared to the input pattern layout. If the width is too large for the combination of overlay elements, the contour printing algorithm may be modified. Thus, the contour printing algorithm can learn itself. Parameters related to the ink flow effect are input into the ink flow algorithm to compensate for the deficiency. This deficiency can be compensated for in subsequent printing. Preferably, the width W is the only dimension that needs to be measured by the test pattern.

Fig. 16 a-16 c show in exemplary illustration a test pattern comprising a set of two overlay elements. The resulting width W0 or W1, indicated by the bold lines and arrows, is obtained by applying the subsequent adjacent covering elements for a predetermined time interval Δ t. The time interval is the delay time for depositing a subsequent adjacent overlay element. The cover elements are strip-shaped elements extending in the Y direction and are arranged at a distance Δ x from each other. The first overlay element is printed and after a predetermined time interval Δ t, the second overlay element is printed at a predetermined spacing Δ x adjacent the first overlay element. The outline may be printed first by printing a first overlay element and then the inner area by printing a second overlay element. The first overlay element may be an outline portion and the second overlay element may be an inner region portion.

FIG. 16a shows the impact of the reduction in ink flow impact. The test pattern includes two equal overlay elements s 1. The combination of two s1 overlay elements results in a reduction in the time interval Δ t by applying 5 seconds. The width of the resulting ink pattern measured is W0, which is less than the desired width W1.

Fig. 16b shows the same combination of two overlay elements as shown in fig. 16a, but by applying a time interval Δ t of 10 seconds. The width of the resulting ink pattern is now W1. The results of the ink flow effect dependent on the time interval at can be stored in the control electronics of the ink jet system.

Fig. 16c shows an alternative combination of overlay elements to achieve an ink pattern having a width W1. The first overlay element 1 is combined with the second overlay element 2 by applying a time interval deltat of 5 seconds. This combination of s1 and s2 results in a shorter time than the desired W1 compared to the combination of two overlay elements s 1. First, in the outline covering algorithm, the covering element most suitable for the desired outline is selected. Furthermore, to obtain a shorter printing method, it may be preferable to apply a combination as shown in fig. 16c instead of the combination shown in fig. 16 b. The ink jet system can learn itself by measuring the test pattern and is programmed to subsequently select combinations of overlay elements based on the reduction of the printing process.

Fig. 17a and 17b show further exemplary illustrations of two different combinations of test patterns.

In fig. 17a, a test pattern is printed by a combination of two overlay elements s1 and s 0. The first overlay element s1 is formed by positioning six ink droplets in the Y direction at a certain mutual distance. The second overlay element s0 is formed by positioning five ink droplets at a greater mutual distance in the Y direction. The spacing between the first and second elements in the X direction is 50 μm. A time interval of 10 seconds is applied before printing the second overlay element S0.

In fig. 17b, the test pattern is printed by a combination of two overlay elements s1 and s 3. The first overlay element s1 is formed by positioning six ink droplets in the Y direction at a certain mutual distance. The second overlay element s3 is formed by positioning eight ink drops at smaller mutual distances in the Y direction. Now the spacing between the first and second elements is 25 μm in the X direction and a time interval of 5 seconds is applied before printing the second overlay element s 3. The combination of S1 and S3 has a diminishing effect as an ink flow effect. The combination of overlay elements s1 and s3 results in a shorter print time than the width w2 compared to the combination shown in fig. 17 a. In this case, the inkjet system may be programmed to select the combination of s1 and s3 when a short printing time is preferred.

In a variation, the overlay and ink flow algorithms may also be used to determine the location of the filled ink drop to form the inner region.

It should be noted that aspects according to the invention and in particular those mentioned in the claims may be advantageous as such and are considered patentable as such. In particular, it may be advantageous to apply an overlay or ink flow algorithm before generating a set of drop positions independent of whether the outline drops are printed before filling the drops.

Although the invention has been disclosed with reference to specific embodiments, upon reading this specification it will be appreciated by those skilled in the art that changes or modifications may be made from a technical point of view without departing from the scope of the invention as described above and defined by the prefix 974. Modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the appended 974 prefix clause.

Accordingly, a fifth aspect of the present invention provides a method for printing a more accurate ink pattern. In particular, the present invention provides a method of printing an integrated circuit pattern. The method can be implemented in a simple manner by applying the described improvements to the applied algorithm to convert the pattern layout into a set of drop positions.

Fig. 3, 18-22-x relate in particular to a sixth aspect of the invention.

Fig. 3 and 18 depict an ink jet system according to an embodiment of the sixth aspect of the invention. Fig. 3 and 18 depict an ink jet system for depositing material on a substrate S in a desired ink pattern by ejecting droplets of the material toward the substrate according to an embodiment of the present invention. The implementation material is in particular an ink. The ink pattern must be generated according to the pattern layout. The pattern layout is uploaded to the inkjet system as a bitmap, for example. The ink jet system is preferably a drop on demand ink jet system that ejects ink drops only when needed. This is in contrast to continuous ink jet systems in which ink drops are continuously ejected at a predetermined frequency and in which the ink drops required to form a pattern are directed toward a substrate and the remaining ink drops are captured, thereby preventing the remaining ink drops from reaching the substrate.

The ink jet system of fig. 18 is an industrial ink jet system, particularly an IC ink jet system, which is an alternative to more traditional processes for providing a masking layer, for example using photolithographic techniques, for depositing a corrosion resistant material as a masking layer on a Printed Circuit Board (PCB). Because the mask layer can be deposited directly by the inkjet system, the number of processing steps and thus the time for PCB fabrication can be significantly reduced. However, such applications require high drop placement accuracy and high reliability (on a per drop basis).

As depicted in fig. 18, the orthogonal system includes an X-axis, a Y-axis, and a Z-axis, which can be projected onto the inkjet system. The Y-axis is the longitudinal axis. The Y-axis may be defined as a direction extending in the printing direction. The print direction of an inkjet system is defined as the direction of movement of the substrate as it passes the print head assembly in order to print a line onto the substrate. The printing direction corresponds to the travel of the substrate positioning table. The travel of the substrate positioning stage corresponds to the maximum stroke of the substrate relative to the printing assembly.

The X-axis may be defined as a direction perpendicular to the Y-axis. The X-axis extends in a direction transverse to the printing direction. The X-axis is the horizontal axis. The X-axis and the Y-axis define a substantially horizontal plane in the inkjet system.

The Z-axis may be defined as a direction perpendicular to the X-axis and the Y-axis. The Z axis extends in an upward direction. The Z axis is the top-down axis. The Z-axis extends in a substantially vertical direction.

The tilting motion of the direction Rx of rotation about the X-axis can be defined as the rotation of the substrate about a lateral axis.

A rolling motion in a rotational direction Ry about the Y-axis may be defined as a rotation of the substrate about the longitudinal axis. The longitudinal axis extends from the front side to the back side of the substrate.

The rocking motion of the rotational direction Rz about the Z-axis may be defined as the rotation of the substrate about the up-down axis.

To provide a highly accurate ink jet system, the ink jet system IS comprises a pressure frame FF supporting a metrology frame MF from a floor GR. Between the pressure frame FF and the metrology frame MF, a vibration isolation system VIS is provided to isolate the metrology frame MF from vibrations in the pressure frame FF while supporting the metrology frame MF from the pressure frame FF. As a result, a relatively stable and static printing environment may be generated on the metrology frame that is beneficial to accuracy.

The inkjet system further comprises a print head holder H. Here, the print head holder H is stably installed in the inkjet system. The print head holder H is fixedly connected to the metrology frame MF. The print head holder H has a beam-like shape. The print head support extends in the X-direction. The print head holder supports a print head assembly including at least one print head PH. Each print head PH of the plurality of print heads PH comprises one or more, typically a number of nozzles, from which ink droplets can be ejected towards the substrate S. The print head assembly defines a print range in the X direction in which ink drops can be placed during forward or backward rows, which defines the width of the print area PA and a print range in the Y direction that defines the length of the print area PA.

Further, the inkjet system includes a substrate holder SH that supports the substrate S.

The substrate holder SH is movable relative to the print head PH in a printing direction PD parallel to the Y direction in order to let the substrate S pass under the print head assembly. In the present application, a distinction is made between moving the substrate holder from left to right, i.e. in the positive Y-direction, while passing the print head assembly, and moving the substrate holder from right to left, i.e. in the negative Y-direction, while passing the print head assembly, in fig. 18. Moving from right to left will be referred to as forward-facing and moving from left to right will be referred to as backward-facing.

Many configurations of printhead assemblies are possible in order to cover the entire upper surface TS of the substrate S.

In the first configuration, the printing range in this direction is at least as large as the maximum possible size in the X direction of the substrate S that can be supported by the substrate holder SH. In that case, a single row of the substrate support SH may be sufficient to cover the entire upper surface with ink droplets.

The print head of the print head assembly may comprise an array of print head nozzles equally spaced from each other in the X-direction. The spacing between adjacent nozzles may be, for example, about 100 μm. However, the pattern layout for the ink pattern may include traces that are spaced apart by a distance that is less than the spacing between adjacent nozzles. In this case, the print head support may be moved relative to the substrate in a direction transverse, in particular perpendicular, to the printing direction, i.e. the X-axis, to allow deposition of ink droplets on the areas placed between adjacent nozzles. Therefore, in this case, it is necessary to increase the design requirement to comply with the pattern layout through the substrate. Preferably, the relative movement of the print head with respect to the substrate is obtained by moving the substrate in the X-direction.

In the second configuration, the printing range in the X direction is smaller than the maximum possible size in the X direction of the substrate S that can be supported by the substrate holder SH. In that case, a plurality of parallel rows is required to cover the entire upper surface TS of the substrate S. To allow for multiple parallel rows, the print head assembly and/or the substrate holder SH is movable in the X-direction perpendicular to the printing direction PD.

In this embodiment, the print head assembly has a print range in the X direction that is at least as large as the largest possible size in the X direction of the substrate that the substrate holder SH can hold. The print head assembly is mounted stable relative to the metrology frame MF.

In the embodiment of fig. 18 (further illustrated in fig. 19), the substrate holder SH is supported by a substrate positioning stage PS. The substrate positioning stage PS is supported by a metrology frame MF. The substrate positioning stage PS is supported by the metrology frame so that it can move in the printing direction PD, thereby allowing the substrate holder SH to be positioned and hence the substrate S to be positioned in the Y direction. The positioning of the substrate positioning stage is realized using a stage positioning device SD. The stage positioning apparatus includes a stage guide, a stage position measurement system, and a stage actuator.

The table guide is a linear guide. The stage guide means includes a pair of rod-like members for supporting and guiding the substrate positioning stage. The stage guide bears the substrate positioning stage via ball bearings. The table guide is connected to the metrology frame MF. Thereby, vibrations from the ground do not hinder the linear guiding of the substrate positioning table.

The stage position measurement system includes a linear encoder. The linear encoder comprises an elongated scale extending in the Y direction mounted to the metrology frame, and an optical reader mounted to the substrate positioning stage. In operation, the substrate positioning table passes along the ruler to obtain the Y position of the substrate positioning table. Preferably, the table position measurement system comprises two linear encoders. Two linear encoders allow for a more accurate method for positioning the substrate positioning stage.

The stage actuator includes a belt and a driving member. The substrate positioning table is connected to a drive element by a belt. The drive element is mounted to the pressure frame FF. The drive element may comprise a gear and a motor. Thereby, a driving force F is applied between the substrate positioning stage PS and the pressure frame FF. As a result, the driving force F does not interfere with the metrology frame MF, but is transmitted to the ground GR via the pressure frame, resulting in a higher achievable accuracy of the inkjet system.

Control electronics are provided to control the position and velocity of the substrate positioning stage. A constant velocity of the substrate positioning stage may be preferred as it results in a constant frequency of ejected ink drops.

A support positioning device HD is provided between the substrate positioning stage PS and the substrate support SH to position the substrate support SH in at least one degree of freedom. Preferably, at least one degree of freedom is determined by the support positioning device HD, wherein the at least one degree is a printing direction PD, a translation in the Y-direction relative to the substrate positioning stage PS. With this configuration, the stage positioning device SD can be used to coarsely position the substrate holder SH in the hiss printing direction, while the holder positioning device HD can be used to finely position the substrate holder in the printing direction with respect to the print head assembly. The support positioning device HD can also be used to fine-position the substrate support in other directions, for example in the X-direction and/or in the Z-direction, if desired, and can even fine-position the substrate support in rotational directions such as Rx, Ry and Rz.

The support positioning apparatus HD includes at least one support actuator and at least one support position measurement system. Each support actuator and accompanying support position measurement system can determine a single degree of freedom DOF.

In the embodiment of fig. 19, the substrate support SH is connected to the substrate positioning stage PS by a support positioning device HD, wherein all six degrees of freedom are determined by the support positioning device HD. The support positioning device is arranged to position the substrate support SH in all six possible degrees of freedom relative to the substrate positioning stage. The support positioning apparatus includes six support actuators.

In particular, the holder actuator is a voice coil actuator. The support position measurement system may be incorporated in the support actuator. The voice coil actuator may comprise an encoder to measure the position of the movable voice coil actuator body, in particular its translation. The voice coil actuator body may be movable by a stroke of approximately at least 2mm, in particular at least 4mm, more in particular at least 6 mm. The support actuator has a support actuator base connected to the base positioning stage and a support actuator body connected to the base support. The buttress actuator body is movable relative to the buttress actuator base. In particular, the bolster actuator body has a body member that limits only one degree of freedom in the available directions of movement. In particular, the body member has an elongated portion. Especially the body member is in the shape of an antenna. The body member allows movement in five degrees of freedom, but resists movement (more precisely translation) in a direction parallel to the elongate portion.

The support positioning apparatus HD comprises six individual support actuators, wherein each support actuator limits one degree of freedom in translation. Both pairs of holder actuators together limit the rotational freedom in movement.

The support positioning device HD comprises three support actuators arranged in an upward orientation to limit translation in an upward, substantially vertical direction. Each actuator holder has an antenna-shaped body member extending in an upward direction. Further, the holder positioning device HD comprises three holder actuators, which are arranged in a substantially transverse orientation. The support actuators are spaced apart from each other and are placed on top of the substrate positioning stage. In particular the holder actuator, is placed in a substantially horizontal plane. The actuator holder is attached to the lower side of the substrate holder SH. Three upwardly oriented support actuators limit three degrees of freedom by limiting translation in the Z direction, rotation about the X axis, and rotation about the Y axis. Three laterally oriented support actuators limit three degrees of freedom by limiting translation in the X and Y directions and rotation about the Z axis.

As shown in fig. 19, the cross-section around the X-axis of the base support is U-shaped, wherein the U-shape is oriented upside down. The U-shaped base support has a U-base and downwardly extending U-legs. Six support actuators are arranged between the U-legs. Three vertically oriented support actuators are connected to the U-bottom. Two laterally oriented bolster actuators are connected to a first U-leg and one laterally oriented bolster actuator is connected to a second U-leg opposite the first U-leg.

In order to obtain an accurate printing method, it is a prerequisite that the upper surface of the substrate is moved during the printing operation at a constant distance from a set of nozzles of the print head. In the Z direction, it is considered that the nozzle groups are placed in a common plane defining a virtual plane. A virtual plane is defined parallel to the common plane. During the printing operation, the upper surface of the substrate must be moved parallel to this virtual plane to maintain a constant distance of the nozzle to the upper surface of the substrate.

As shown in fig. 20 and 22, the print head PH is supported in a print head support H such that the nozzles are placed parallel to the virtual plane. The print head holder H has at least three reference marks Z1, Z2, Z3 in the Z direction, which define an imaginary plane parallel to the virtual plane. In particular, the print head support H may have a planar reference surface comprising the three reference marks, wherein the planar reference surface is parallel to the virtual plane.

The substrate S is placed on the substrate holder SH. The travel of the substrate in the virtual plane is obtained by moving the substrate holder SH parallel to the virtual plane. In operation, the support positioning device HD is controlled such that the substrate support SH remains positioned parallel to the virtual plane during travel. Despite such deviations caused by, for example, the substrate positioning stage PS. The substrate positioning table is moved in the printing direction with a long stroke of about at least 1 meter, in particular about at least 1.5 meters, wherein deviations in the ideal path may occur. For example, by introducing deviations through the non-straight run of the table guide. The support positioning device HD compensates for deviations introduced by the substrate positioning table during travel. The support positioning device HD is programmed to control the substrate support SH parallel to the virtual plane.

Three reference marks Z1, Z2, Z3 defining a planar reference plane parallel to the virtual plane may be used for homing the substrate holder SH. In the calibration step, the substrate holder SH may be docked to the reference marks Z1, Z2, Z3. The substrate holder may be docked to the print head holder H at a plurality of Y positions of the substrate positioning stage. The substrate holder SH may be butted by or without the supporting substrate S. After docking the substrate support to the reference mark of the print head support, the orientation and position may be defined as the docking position. Each docking position may be stored in the memory of the control electronics CE of the inkjet system as a function of the Y position of the substrate positioning stage PS.

As shown in fig. 22, the inkjet system, particularly the print head support PH, may further comprise at least one Z sensor "Z" for measuring the Z distance from the print head support H to the upper surface of the substrate S or to the upper surface of the substrate support SH. Preferably, the ink jet system IS comprises two Z-sensors directed onto the upper surface associated with IS to maintain a constant distance between the virtual plane and the upper surface of the substrate S. The relevant surface may be the upper surface of the substrate holder SH or the upper surface of the substrate on top of the substrate holder SH. The at least one Z-sensor is stably mounted to the metrology frame MF. In particular, the Z-sensor is an optical distance sensor for measuring the distance between the sensor and the target surface. Specifically, the at least one Z sensor is mounted to the print head support H. In the printing method, the at least one Z-sensor may be used to verify the distance in the Z-direction of the substrate S with respect to the virtual plane, the Z-distance. It is desirable that the virtual plane defined by the print head nozzles and the upper surface of the substrate S be a constant distance in the Z-direction. The at least one Z-sensor may generate a signal to the control electronics CE of the ink jet system if a deviation over a constant Z-distance is detected. The first Z sensor may be mounted to the print head support H to verify the first degree of freedom as a constant Z distance. The second Z-sensor may be placed relative to the first Z-sensor and mounted onto the print head support H to additionally verify the second and third degree of freedom DOF, which means verification of the rotation Rx around the X-axis and/or the rotation Ry around the Y-axis. Preferably, the first and second z-sensors are aligned in the X-direction to verify the z-distance and rotational freedom around the Y-axis. In a step in the printing method, the control electronics can control the support positioning device HD to be in a suitable position to compensate for the detected deviation in at least one degree of freedom. Another option is that the control electronics are programmed to interrupt the printing method to perform a subsequent calibration step. During the compensating step, a step of printing an ink pattern onto the substrate may be performed.

Fig. 19 further shows a scanning unit SU for scanning the substrate. The scanner unit is mounted on a metrology frame MF. An upper surface of the substrate serving as a reference surface is scanned by a scanning unit. The reference surface of the substrate is provided with at least one reference member. In particular, the reference surface of the substrate is provided with two reference members. The position of the reference member in the X-Y plane is determined by the scanning unit SU. By scanning at least two positions, the rotational deviation of the substrate S with respect to the Z-axis is determined. After the rotational deviation is determined, the rotational deviation is compensated for by controlling the substrate holder SH to rotate the substrate S about the Z axis.

Fig. 21 shows a further step of the calibration method according to the invention. Fig. 21 shows in a schematic view the substrate holder SH guided by the substrate positioning stage PS. The travel of the substrate positioning stage PS introduces a deviation in the ideal straight-line trajectory in the X-direction. The base support SH includes a support position measurement system. The support position measurement system comprises at least one sensor, known as an X-sensor and an X-calibration element, guided in the X-direction. The X collimating element is beam-shaped and extends in the Y direction. The X calibration element is mounted to the metrology frame MF. The calibration element XCE is arranged parallel to the substrate positioning table guide PSg. The calibration element XCE has a flat surface, which is used as an X-reference surface. The X reference surface of the calibration element has a flatness around 100 μm. In particular, the support position measurement system comprises at least two sensors directed in the X-direction. The at least two X-sensors are configured to measure a distance between the substrate support and an X-reference plane of the calibration element. At least two X sensors are spaced apart from each other in the Y direction by a predetermined displacement of about 'S'. At least two X-sensors are arranged at substantially the same height as the substrate holder, whereby the sensors measure the distance from the substrate holder to the reference surface of the calibration element along the same sensor path P.

First, the measurement of the sensor determines the X-offset of the substrate positioning stage in the X-direction relative to the calibration element. Second, the measurement of the at least two X sensors at a predetermined displacement "S" can be used to determine the flatness of the calibration element reference surface as a function of the Y position of the substrate positioning stage. The first sensor measures a first relative distance X1 at a particular Y position and the second sensor measures a second relative distance X2 at the same Y position. The measurement of the relative distance may be performed for approximately the full travel distance of the substrate positioning stage to output a set of X1 values and a set of X2 values as a function of the Y position. The distance 'S' between the first and second sensors is known, which means a shift in the Y direction of the measured X1 and X2 values. By comparing the two sets of measured values X1 and X2 at the first and second Y positions along the longitudinal axis corresponding to a shift of distance "S", the planarity of the calibration element can be determined. Subsequently, the flatness of the calibration element may be taken into account during the controlled movement of the substrate positioning stage. The flatness of the calibration element and the X-deviation can be compensated together in a feed forward control controlled by the control electronics. The deviation in the X direction, known as the measured value of the X deviation, for the travel of the substrate positioning table in the Y direction along the substrate, can be stored in a memory of the control electronics. The X offset may be stored in a table. The support positioning device is configured to compensate for an X-deviation as a function of the position of the substrate positioning stage. During a printing operation, the stored X offset as a function of the position of the substrate positioning table along the longitudinal axis may be used to move the substrate support in the opposite X direction to null the X offset.

Similar to compensating for the X-bias in the X-direction, compensating for the Z-bias in the Z-direction may be performed. The travel of the substrate positioning stage PS introduces a deviation in the ideal straight-line trajectory in the Z-direction. The substrate holder SH includes a holder position measurement system. The support position measurement system includes at least one sensor (known as a Z-sensor Zs1) directed in the Z-direction and a Z calibration element. The Z-alignment element is beam-shaped and extends in the Y-direction. The Z calibration element ZCE is mounted on the metrology frame MF. The Z alignment element is arranged parallel to the substrate positioning table guide PSg. The Z calibration element has a flat surface which is used as the X reference surface. In particular, the same X calibration, XZ calibration element used to measure X offset can also be used to measure Z offset. The XZ calibration element may include a first reference surface, the X reference surface, to measure X deflection and a second reference surface, the Z reference surface, to measure Z deflection. The Z reference surface of the calibration element has a flatness around 100 μm. In particular, the support position measurement system comprises at least two Z sensors Zs1, Zs2 directed in the Z direction. The at least two Z sensors are configured to measure a distance between the substrate support and a Z reference surface of the Z calibration element. At least two Z sensors are spaced apart from each other in the Y direction by a predetermined displacement of about 'S'. At least two Z-sensors Zs1, Zs2 are arranged at substantially the same position as the substrate holder in the X-axis along the transversal direction, such that the Z-sensors measure the distance from the substrate holder to the reference surface of the calibration element along the same sensor path P.

First, the measurements of the Z-sensor determine the Z-offset of the substrate positioning stage relative to the calibration element in the Z-direction. Second, the measurement of the at least two Z sensors at a predetermined displacement "S" can be used to determine the flatness of the Z calibration element reference surface as a function of the Y position of the substrate positioning stage. The first sensor measures the first relative distance Z1 at a particular Y position and the second sensor measures the second relative distance Z2 at the same Y position of the substrate positioning stage PS. This measurement of relative distance may be performed for approximately the full travel distance of the substrate positioning stage to output a set of Z1 values and a set of Z2 values as a function of Y position. The distance 'S' between the first and second sensors is known, which means a shift in the Y direction of the measured Z1 and Z2 values. By comparing the two sets of measured values Z1 and Z2 at the first and second Y positions along the longitudinal axis corresponding to a shift of distance "S", the planarity of the Z calibration element can be determined. Subsequently, the flatness of the Z calibration element may be taken into account during the controlled movement of the substrate positioning stage. The flatness of the calibration element and the Z-bias can be compensated together in a feed-forward control controlled by the control electronics. The deviation in the Y direction for the travel along the substrate positioning table in the Z direction, known as the measured value of the Z deviation, can be stored in the memory of the control electronics. The Z offset may be stored in a table. The travel of the substrate positioning device is regenerated. The support positioning apparatus is configured to compensate for Z offsets as a function of the position of the substrate positioning stage. During a printing operation, the stored Z offset as a function of the position of the substrate positioning table along the longitudinal axis may be used to move the substrate support in the opposite Z direction to null out the Z offset.

In a further embodiment of the ink jet system according to the invention, the substrate holder comprises at least a third sensor, also called Z3-sensor, for measuring the relative distance in the Z direction between the substrate holder and the Z reference surface of the calibration element. The at least third Z3 sensor is arranged at a predetermined distance (shift) in the X direction from at least one other Z sensor. In particular, the at least three Z-sensors may be used to provide a more accurate positioning of the substrate support in the Z-direction and a more accurate rotational positioning around the longitudinal axis Ry. Although the present invention has been disclosed with reference to particular embodiments, it will be appreciated by those skilled in the art from a reading of the specification that changes or modifications may be made without departing from the scope of the invention as described above and in the following claims. Modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the sixth aspect of the invention disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the appended 975 prefix clause.

Fig. 23-25 relate in particular to a seventh aspect of the invention.

Fig. 23a shows an embodiment of the substrate conveyor 1 according to the seventh aspect of the invention in a top view. The substrate conveyor 1 is arranged for moving a substrate in an inkjet system. The substrate conveyor comprises a conveyor body 10 and a conveyor guide 19. The conveyor body 10 comprises a conveyor support surface 15 for supporting the substrate during movement of the conveyor body 10. The conveyor guide 19 is arranged for guiding the conveyor body 10. In particular, the conveyor guide 19 is arranged for linear or rotary guiding of the conveyor body 10.

The substrate conveyor 1 may be arranged as a printing conveyor to convey substrates through a printing zone of an inkjet system. The substrate may be moved linearly along the print head by a print conveyor for depositing ink onto the substrate. Alternatively, the substrate conveyor 1 may be arranged as a station conveyor for processing substrates in stations. The stations may be buffer stations, power supply stations, egress stations, roll-over stations, and the like. The station conveyor may be included in a buffer station for buffering the substrate or a flipping station for turning the substrate upside down.

The conveyor main body 10 has a rectangular shape. The conveyor body 10 has four side faces 11, 12, 13, 14, a top face 15 and a bottom face.

The conveyor body 10 has a front face 11, a rear face 12 and two lateral side faces 13, 14. The conveyor body has a longitudinal axis L which extends from the front face 11 to the rear face 12. The transverse axis may be defined in a direction perpendicular to the longitudinal axis L. The substrate may be transferred to or away from the conveyor body 10 in the conveying direction T by passing through the front face 11 or the back face 12. Double-sided arrows are shown in fig. 1 to indicate the transport direction T. The conveying direction T is parallel to the longitudinal axis L of the conveyor body 10.

The top surface 15 is arranged as a conveyor support surface. The conveyor support surface 15 is planar to support a flat substrate. The conveyor supporting surface 15 is subdivided into at least one engagement area. The plurality of engagement regions allow engagement with a variety of substrate sizes. The conveyor support surface 15 includes at least one gas opening 151 in fluid communication with the at least one gas groove for conducting gas into or out of the conveyor support surface. The at least one gas opening 151 may be used to engage the substrate on a conveyor support surface of the conveyor body. The conveyor support surface 15 includes a plurality of gas openings 151 that maintain the substrate in abutting engagement with the conveyor support surface by suction through the gas openings 151. A plurality of gas openings are placed in the grating. During movement of the conveyor body, the substrate may engage the conveyor support surface by a suction force that draws gas from the gas opening. During the transfer, the substrate may be brought into a floating state relative to the conveyor support surface by supplying gas through the gas opening.

The conveyor main body 10 is supported by the conveyor guide 19. A conveyor guide 19 is provided on the bottom surface of the conveyor main body 10. Here, the conveyor guide is a linear guide for linearly moving the conveyor main body. Here, the conveyor guide defines a conveying direction of the conveyor body, which is parallel to the longitudinal axis L and the conveying direction T.

Further, the substrate conveyor 1 comprises a transfer unit 20. The transfer unit 20 comprises at least one clip 22 arranged to engage an edge of the substrate. The clip is shown in further detail in figure 3. The transfer unit 20 includes two clips 221, 222. The two clips grip the substrate at two locations at the edge of the substrate. Advantageously, the two clamps prevent rotational movement of the substrate during the transfer movement.

The at least one clip is attached to a clip support 21. The clip holder 21 is arranged for holding at least one clip 22. The clip holder is beam-shaped. The clip holder 21 has an elongated shape. The clip supports 21 extend across the full width of the conveyor body 10. On both lateral sides of the conveyor body 10, clip holders 21 are supported by conveying guides 23. A transport guide 23 is provided for guiding the clip holder 21. The transport guide 23 provides linear movement in the transport direction T to the clip support 21. The transfer guide 23 is mounted to the conveyor body 10. The transfer guide 23 includes two transfer rails 231, 232. The two transfer rails 231, 232 extend along the longitudinal axis of the conveyor body 10. Two transfer rails extend along the lateral sides of the conveyor body 10. The first transfer rail 231 is connected to one lateral side of the conveyor body 10. The second transfer rail 232 is connected to the opposite lateral side of the conveyor body 10.

Fig. 24a and 24b show a more detailed view of the transport unit 20 in schematic side views. The transport unit comprises transport guide means 23 for guiding the clip holder 21. The clip holder 21 includes a slidable clip holder portion 21a slidable in the conveying direction T and a dynamic clip holder portion 21b movable in the upward direction U. The sliding clip holder portion 21 has a bearing sleeve 213 to support the clip holder 21 on the conveying guide 23.

The clip holder portion 21a includes first and second holder actuators 211. A first support actuator (not shown) is provided for moving the clip support 21 along the transport guide 23. The first support actuator comprises, for example, an electric motor with a belt drive or a rack and pinion drive.

A second bolster actuator 211 is provided for moving the dynamic clip bolster portion 21b from the raised position to the lowered position. Fig. 24a shows the transfer unit 20 in a lowered, also called lowered, position. Fig. 24b shows the transfer unit 20 in the raised position. In this lowered position, the transfer unit is placed below the height defined by the conveyor supporting surface of the conveyor body. In the raised position, the gripper 22 of the transfer unit reaches a height above which it can grip the end of the substrate to pass over the support surface of the conveyor. The movement of the clip holding portion 21b from the raised to the lowered position defines the up-down direction indicated by the double-sided arrow U. The up-down direction is a substantially vertical direction. The up-down direction is directed substantially perpendicular to the longitudinal axis and perpendicular to the transverse axis. The movement of the clip support 21 in the up-down direction has a stroke of at least 3 mm, in particular at least 5 mm, more in particular at least 8 mm.

The second holder actuator 211 includes a voice coil actuator for actuating the dynamic holder portion 21b and a clip holder guide 212 for guiding the dynamic clip holder portion 21b in the up-down direction. The clip holder guide 212 includes at least one spring piece for elastically connecting the dynamic clip holder portion 21b with the slide clip portion 21 a. In this case, the elastic connection is provided with two spring pieces arranged in parallel at both ends of the clip support 21. Advantageously, the elastic connection by the spring plate can provide a hysteresis-free connection with relatively fast dynamic properties.

Fig. 25a shows the clip 22 in further detail. The clip 22 has an elongated and beam-like clip outer profile. The elongated outer profile defines a length direction. The clip 22 is adapted to be placed parallel to the length of the elongate clip support 21. As shown in fig. 25b, the clip 22 may be placed in a lowered position relative to the upper surface of the clip support 21. Due to its rectangular geometry, the clip 22 can be nested into the clip holder 21 to achieve a compact configuration. In particular, the clip holder 21 holds two clips 22, as shown in fig. 25b, wherein the clips 22 are aligned with each other in the length direction.

The clip 22 has a clip opening 223 which extends in the transverse longitudinal direction. The nip has an upper nip portion 223b and a lower nip portion 223 a. The desired clip mouth portion 223a is attached to the first clip sub-frame 224 a. The upper clip mouth portion 223a is connected to the second clip sub-frame 224 b. The second clip sub-frame 224b is movably connected to the first clip sub-frame 224a by a sub-frame guide 225. The subframe guide is resilient and comprises two spring plates arranged in parallel. In the assembly of the clip 22 to the clip holder 21, the lower jaw portion 223a is stably installed and the upper jaw portion 223a is movably installed with respect to the lower jaw portion 223 b. In the assembly of the clip 22 to the clip holder 21, the first subframe 224a is mounted to the clip holder 21.

The clip 22 includes a clip actuator 226 for actuating the clip opening. In the assembly with the clip support 21, the clip actuator is stably mounted to the clip support by the third clip sub-frame 224 c. The clamp actuator comprises a pneumatic cylinder, in particular a pneumatic cylinder. The cylinder includes a piston rod 2261 that is movable from a return to an extended position (and vice versa). At least one clip runner 2262 is attached to the end of the piston rod. Clip runner 2262 is movable along runner surface 2242. The second clip sub-frame 224b includes a wedge shaped element 2241. Runner surfaces 2242 are provided on the wedge elements 2241. The wedge member is fixedly connected to the upper mouth portion 223 b. Here, the clip comprises two wedge-shaped elements arranged in parallel. Two clip runners are connected to the piston rod. The upper mouth portion 223b may be moved towards the lower mouth portion by moving the piston rod to the extended position. Clip runner 2262 is run along running surface 2242 by moving the piston rod to the extended position. During movement, clip runner 2262 is pressed onto runner surface 2242, thereby moving upper mouth portion 223b in a direction toward lower mouth portion 223 a. The sub-frame guide is resilient to return the upper mouth portion 223B away from the lower mouth portion when the clip runner moves back to the returned position.

Although several aspects of the present invention have been disclosed with reference to specific embodiments, upon reading the present specification those skilled in the art will appreciate that variations or modifications can be made from a technical standpoint without departing from the scope of the present invention as described above and in the claims that follow. Many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the claims and the appended claims.

Accordingly, a first aspect of the invention provides a printing method comprising an embedded quality check to check for printing errors on a printed ink pattern. Advantageously, the substrate can be inspected and rejected or approved before further processing, which increases the efficiency of the printing process. The present invention provides further refinements to embedded quality inspection by extracting control features from the raster input image in the preparation step to increase the speed of the final quality inspection. Further, the present invention provides an ink jet system for performing the printing method according to the present invention.

Claims (20)

1. A printing method for printing an ink pattern on a substrate based on an available pattern layout, wherein the pattern layout defines a desired layout of the ink pattern to be printed, the method comprising the steps of:

providing an inkjet system comprising a frame for supporting components of the inkjet system, a printhead assembly for ejecting ink drops onto a substrate, wherein the printhead assembly is mounted to the frame, a scanning unit for scanning an ink pattern printed on the substrate, wherein the scanning unit is mounted to the frame of the inkjet system, and control electronics for controlling the inkjet system;

providing a substrate to be printed;

generating an input image for dispensing dot locations of an ink pattern to be printed by a printhead assembly, wherein the input image is based on a pattern layout;

printing an ink pattern onto a substrate by a print head assembly of an inkjet system based on an input image;

scanning the printed ink pattern by a scanning unit of the inkjet system to obtain a scanned image of the printed ink pattern;

performing an embedded quality check on a board of the inkjet system controlled by control electronics of the inkjet system by comparing the scanned image to the pattern layout to detect any printing defects in the printed ink pattern and provide a decision to approve or reject the printed ink pattern on the substrate; and

the substrate is transported from the inkjet system to a subsequent processing station for further completion of the substrate, in case of approval, or the substrate is discharged in case of rejection.

2. The printing method of claim 1, wherein the input image is a raster input image generated by rasterizing the pattern layout into a raster input image for assigning dot positions of an ink pattern to be printed by the printhead assembly.

3. A printing method according to claim 1 or 2, wherein the printing method further comprises the step of, in the event of rejection, discharging the rejected substrate to a discharge station for storing at least one rejected substrate.

4. The printing method according to claim 1, wherein the substrate is temporarily stored in a buffer unit of the inkjet system, the quality inspection of the substrate is performed while the substrate is temporarily stored in the buffer unit, and the subsequent substrate is printed in a printing zone of the inkjet system at the same time.

5. The printing method according to claim 4, wherein the printing method comprises a step of receiving the substrate having the printed top side from a printing area of the inkjet system in a rotation buffer unit for temporarily storing and inverting the substrate, and a step of resupplying the substrate to the printing area of the inkjet system for subsequent printing of the bottom side of the substrate, wherein the first quality inspection is performed on the ink pattern printed on the top side of the substrate while the substrate is stored in the rotation buffer unit.

6. The printing method according to claim 1, wherein the printing method further comprises the steps of:

preparing a quality check by filtering at least one control feature from the input image, wherein the at least one control feature defines a candidate defect of the ink pattern; and

a quality check is performed by comparing at least one control feature of the input image with the scanned image.

7. A printing method according to claim 6, wherein filtering the control features from the input image is performed at least partly simultaneously with performing the step of printing the ink pattern and/or the step of scanning the printed ink pattern.

8. A printing method according to claim 6 or 7, wherein the plurality of control features are grouped according to the type of control feature.

9. A printing method according to claim 6 or 7, wherein the control features are identified by applying a mask to the input image to filter the control features.

10. A printing method according to claim 6 or 7, wherein the filtering of the control features comprises at least one selection criterion to filter at least one key portion of the input image.

11. The printing method according to claim 1, wherein the step of scanning is performed by a scanning unit comprising a light source for illuminating at least a part of the ink pattern of the substrate and an imaging unit for capturing at least a part of the scanned image, wherein the light source emits a color of light corresponding to an extreme light reflectance value of the background surface of the substrate or the ink pattern.

12. Manufacturing method for manufacturing an electronic substrate comprising a printing method according to any of claims 1-11, wherein the manufacturing method further comprises a step of etching the substrate, wherein the step of performing a quality check for printing errors is performed before starting the step of etching the substrate.

13. Use of the printing method according to claim 1 for manufacturing an electronic substrate.

14. Ink jet system for industrial applications for printing ink patterns on a substrate, comprising

A frame for supporting the ink jet system assembly;

a substrate conveyor for carrying and moving the substrate;

an ink jet print head assembly for ejecting ink drops onto a substrate to print an ink pattern on an upper surface of the substrate, the ink jet print head assembly being mounted on a frame;

a scanning unit for scanning the printed ink pattern of the substrate, which is mounted on the frame;

control electronics for controlling an inkjet system, wherein the control electronics are configured to perform the embedded quality check on a plate of the inkjet system in the step of performing the printing method according to any one of claims 1 to 11.

15. The inkjet system of claim 14, wherein the control electronics include a logic unit configured to perform a quality check by comparing a raster scan image generated from the scanning unit with a raster input image generated from the received pattern layout.

16. Inkjet system according to claim 14 or 15, wherein the logic unit is embedded in the chip.

17. Inkjet system according to claim 14, wherein the inkjet system comprises a buffer unit for temporarily storing the substrate, wherein the quality check performed on the substrate is performed to temporarily store the substrate in the buffer unit while a subsequent substrate is printed in the printing zone of the inkjet system.

18. The ink jet system according to claim 17, wherein the buffer unit is a rotation buffer unit for temporarily storing the substrate and reversing the substrate, wherein the rotation buffer unit has a rotation unit for reversing the rotation of the substrate.

19. Inkjet system according to claim 14, the scanning unit comprising a light source for illuminating at least a part of the ink pattern of the substrate, wherein the scanning unit comprises an imaging unit for capturing a scanned image, wherein the light source is arranged to provide illumination of the ink pattern with a specific light color tuned to extreme reflectance values of the ink pattern and/or the background surface.

20. Substrate production line for manufacturing electronic substrates, comprising an inkjet system according to any one of claims 14-19 and further comprising an etching station for etching the substrate, wherein the etching station is placed downstream of the inkjet system with respect to a main production flow of the substrate, wherein the main production flow comprises a sub-flow placed upstream of the etching station for ejecting the substrate from the main production flow after performing a quality check on the printed ink pattern.