HK1056611B - A method for individualised marking of circuit boards - Google Patents

Description

Method for the distinctive marking of circuit boards

Technical Field

The invention relates to a method for the distinctive marking of printed circuit boards by means of an exposure method in the manufacture of circuit boards.

Background

In industrial manufacturing processes, and in particular in the assembly industry, it is important to be able to identify the elements used in assembly for each respective component separately. Instructions for assembly and/or for carrying out tests and tests related thereto are also required in the assembly. It is also often desirable to be able to track the lot size of components or the date of manufacture of the components. To solve these identification problems, the components are marked, for example, by sticking labels thereto, by hand, by means of a laser or an ink-jet printer, or by other corresponding marking methods. In some assembly processes, the assembly line comprises a marking unit at the beginning, in which the component or certain components are marked, for example with a mark representing a batch. However, this type of marking unit is generally expensive and takes up a lot of space. Furthermore, this marking process becomes a separate working phase. In some manufacturing processes, for example in the manufacture of plastic products, batch-related marking can be carried out during the manufacture of the products by means of mould parts (parts being exchangeable in batches) which are included in the mould for manufacturing the products, but the products cannot be distinguished from one another by this method.

In circuit board technology, the code of the circuit board or of the finished product assembled thereon may be contained in the etch pattern of the circuit board, whereby markings may be made during the manufacturing process of the circuit board. Typically, such marking is accomplished by incorporating the desired marking into the films used in the manufacture of the circuit board. However, the marks formed in this way cannot be changed during the manufacturing process of the circuit boards, and therefore an identifier for distinguishing each circuit board manufactured cannot be realized by these methods.

Currently, circuit boards are marked by laser machining to write or use printed adhesive bar code labels.

Laser marking is very dirty because of the large amount of dust and gas generated. Furthermore, laser marking devices are expensive and take up a lot of space. Since there must be one marking device at the beginning of each production line, several devices are required. The problems with adhesive labels are their price, and their positioning and assembly in relation to the electronics that are currently packaged in very small spaces. Adhesive labels are more difficult to place than conventional surface mount devices. In addition, adhesive labels must withstand the welding and cleaning processes. The marking required by the packing density of current electronic devices is very small.

It is not desirable to employ the technique disclosed in publication GB 1471163 for marking printed circuit boards throughout the entire manufacturing process. It is not usually practical to remove the photoresist from the surface of the circuit board and leave it only for the serial number, especially by heating the fixed photoresist. This technique described essentially replaces the silk-screen markings currently in use. This known method does not involve distinctive identification marks, for example with serial number marking in a manner according to the invention.

Publication DE 3620850 discloses marking on a carrier film by irradiating the film with a marking. For lighting devices, point sources are used, such as LEDs or end points of optical fibers. Irradiation by a film bearing a marking is not suitable for forming a distinctive identification mark on a circuit board during its manufacture. This publication does not disclose that the exposure is performed on the photosensitive surface of the circuit board.

Publication US 4806965 discloses a matrix printer for marking on a photosensitive material of a moving film. This arrangement is somewhat the same as known thermal printers in which the ink ribbon passes under the recording head. Among other things, this publication discloses interlacing of the matrix. The exposure techniques disclosed herein are not suggested for use in distinguishably marking circuit boards.

Publication DE 3147994 discloses a method for batch-specific marking of circuit boards. However, although this method employs numeric characters recorded on a photosensitive material for distinguishing each lot, this method does not involve marking a mass-produced product in order to mark the circuit board blank itself. This method does not involve marking by direct exposure on the surface of the circuit board, but involves producing a film to be transilluminated for marking by a special intermediate stage.

The publication US 5337117 shows the production of a photo mosaic (photomosaic) from several different negative films by multiple exposures on the film. The exposure technique described in this publication is not suitable for distinguishing markings, i.e. the marking of individual products is differentiated from the marking of individual products by means of photolithographic techniques.

Indicia refers primarily to a visually detectable graphic on or within the surface of a product that is distinguishable from the surface of the product or within the product.

The indicia has previously been primarily a logo, alignment indicia, various graphic or alphanumeric indicia. The marking may also be information in encoded form, for example in the form of a bar code, or information represented by other encoding methods, such as a so-called two-dimensional (2D) code.

In many applications, the indicia are permanent, or at least difficult to remove and/or alter.

In the manufacture of circuit boards, for example, copper-coated fiberglass boards are used. The copper surface of this plate is coated with a photosensitive coating. The coating is exposed through a suitable film or mask and the desired portions of the surface are etched away using known techniques, thereby leaving the desired pattern on the surface of the glass fiber sheet. In the manufacture of circuit boards, it is also possible to use the so-called adhesive method, in which, for example, electrolysis is used instead of etching to form the desired pattern. However, a common feature of the different manufacturing methods is that the surface of the circuit board material is provided with a photosensitive coating when the desired pattern is formed. The desired pattern is often made as a so-called contact print, in which case the film or mask contained by the pattern is located on top of the photosensitive coating during exposure. The light used in the manufacture of the circuit board may be visible or outside the visible spectrum, depending on the coating used.

Disclosure of Invention

It is an object of the present invention to provide a method for marking on a circuit board, wherein at least a part of the surface of the circuit board is coated with a photosensitive material during at least a part of a manufacturing process cycle in order to manufacture the circuit board. The method relating to the invention is characterized in that on each circuit board blank, on the photosensitive surface required for the manufacture of the circuit board, a machine-readable pattern is exposed for the subsequent use in the manufacture of the product itself for distinguishing said circuit boards.

Codes related to the invention covering several tens of characters have a dimension of only a few millimeters in each direction at normal etching accuracy, which is required for example when manufacturing cameras, mobile phones and watches. The required lithography is performed approximately ten times cheaper than a laser machining apparatus. Furthermore, the marking device is arranged in connection with the production line of the circuit board factory, for example at its very beginning, and not in the electronics factory itself. In this way, the marking can be concentrated in a few locations and can be performed by means of cheaper devices. Furthermore, the circuit boards can be distinguished when the manufacturing process has already started. In this way, the individual circuit boards can be monitored individually already from the beginning of the first exposure phase. According to the present invention, only one additional exposure or masking process is required in the normal exposure.

The invention achieves additional advantages with respect to the prior art being used and known to the applicant, since by this means the circuit board can be marked even before the pattern on the circuit board has been etched, for quality control already at the first stage of manufacture. The circuit boards can thus be distinguished by marking them before the actual electronic components are assembled. Such a marking is used in a factory where electronic devices are manufactured from circuit boards.

The method relating to the invention is particularly suitable for marking on circuit boards, since the manufacturing process involves at least partially treating the surface of the circuit board with a photosensitive material. According to a preferred embodiment of the invention, the marking is performed during the manufacturing process of the circuit board and takes place simultaneously with the processing of the circuit board. Instead of visible light and coatings sensitive thereto, other radiation types and coatings sensitive thereto may also be used in the method relating to the invention. For clarity, the terms "light" and "photosensitive" as used in this specification also refer to other types of radiation used in the manufacture of products.

The method relating to the invention is characterized in that the marking is carried out on that part of the surface of the circuit board which has been treated with a photosensitive material as part of the manufacturing process of the circuit board or for marking purposes.

The invention is particularly suitable, for example, for marking on single-layer or multilayer circuit boards. According to a preferred embodiment of the invention, the desired marking is performed on the circuit board or on a layer of the multilayer board while the pattern to be etched is formed. With the method of the present invention, it is possible to mark each layer of the multilayer sheet or only selected layers. When marking is performed using the same process as the manufacture of the circuit board itself, the marking is as permanent and accurate as other patterns formed on the circuit board. The indicia will also be protected in the same manner as the pattern on the circuit board forming the circuit board itself.

The marks formed according to the method of the invention may be formed on the surface of a circuit board or on a coating formed during the manufacture of the circuit board.

With the method of the invention all circuit boards manufactured are provided with individual markings before their assembly for use.

The indicia formed according to the method of the present invention may be machine readable. The marking can also be made very small in size, the limiting factor of which is the manufacturing process and its capacity, such as the smallest possible swath width achievable in circuit board manufacturing.

The marking formed according to the method of the present invention preferably contains information identifying and/or distinguishing the circuit board or the product manufactured with the circuit board. The indicia may also contain information regarding the manufacturing, testing, inspection, packaging or other manipulation of the product and/or subsequent use of the product, or a combination of such information. By forming machine-readable indicia relating to manufacturing or other handling processes, the indicia may be used to control the manufacturing and other handling processes of a product, such as for controlling the mechanization or assembly of a circuit board or product manufactured therewith.

The indicia may be constituted by alphanumeric or numeric characters or may be constituted by a graphic or a plurality of graphics and combinations thereof, which form a graphic recognizable as a code and/or usable or desirable for use as a code. In a preferred embodiment of the invention, the indicia is, for example, a bar code or other binary code, such as a so-called two-dimensional (2D) code.

According to a preferred embodiment of the present invention, the mark formed on the product is constituted by at least a portion indicating the kind or type of the circuit board and/or a portion indicating the lot size. In addition to this information, the label also includes a portion that distinguishes each circuit board that is made. According to a preferred embodiment of the invention, this distinctive part is evident for each product, preferably, for example, a consecutive number or a corresponding code. According to another preferred embodiment of the invention, the mark is formed containing information about the production line or the manufacturing process of the product.

According to a preferred embodiment of the invention, the quality of the processed mark can be compared with the proof mass by means of a special reader (checker), and the detected quality of the mark can also be used to check the quality of the manufacturing process. Several such markings may be present on the product, as well as other markings related to the quality of the product, also for identification and other purposes as described above.

The apparatus for performing the method of the invention comprises at least one light source and an adjustable means for directing light from the light source according to a pattern corresponding to the marks on the light-sensitive surface of the product to be marked.

In a preferred embodiment of the invention, the means for allowing light from the light source to pass to the light-sensitive surface of the product are constituted by light source means arranged in a beam of light directed at the surface to be marked, said means comprising a plurality of areas, the transparency of which can be adjusted by means of control means so as to be transparent or opaque, such as a Liquid Crystal Display (LCD). These means with adjustable transparency are preferably controlled by means integrated in the manufacturing process of the product or in connection with the control thereof, but they may also be controlled by means of the apparatus itself. As means for allowing light to adjustably pass through it is also possible to use, for example, various membranes, films and/or combinations thereof, by means of which a pattern corresponding to a desired marking can be formed, for example by placing these membranes or films or other suitable means in place of each other.

According to another preferred embodiment of the invention, the method-implementing means comprise optical means (e.g. one or more lenses) between the light source and the means with adjustable transparency, and/or optical means (e.g. one or more lenses) between the means with adjustable transparency and the light-sensitive surface of the product. According to a preferred embodiment of the invention, the optical means between the means with adjustable transparency and the photosensitive surface portion of the product are formed in such a way that the pattern transferred (e.g. projected) through them onto the surface of the product is a pattern adjusted on the means with adjustable transparency or a reduced pattern thereof. In another preferred embodiment according to the invention, the optical means form a pattern on the surface of the product that is adjusted by means having an adjustable transparency, or an enlarged pattern thereof.

In another preferred embodiment of the invention, the adjustable transparency means is arranged at the position to be marked against or near the surface of the product to be marked. When marking is performed on a circuit board, the position on the circuit board where the marking is to be performed is determined in advance, for example, in relation to the design of the circuit board. In a film used in circuit board manufacturing, it is easy to form a region corresponding to a space required by marking on a circuit board surface, and to process the region on the film so that a photosensitive surface of the circuit board can be exposed in the region for marking.

According to a further preferred embodiment of the invention, the means for allowing light to pass onto the surface of the product are constituted by a bundle of optical fibers, each having one end located in the vicinity of the light source and the other end in the vicinity of the portion of the photosensitive surface of the product to be marked. By means of suitable control means, light from one or more light sources is guided to the ends of the individual optical fibers at the end of the bundle on the side of the light source, so that the light passing through these optical fibers will form a pattern corresponding to the desired marking on the light-sensitive surface part of the product.

According to a further preferred embodiment of the invention, as light source the same light source is used as is used for processing the product in the product manufacturing process. In a preferred embodiment of the invention, the means with adjustable transparency included in the marking device of the invention are assembled together with optical means included in the means of the apparatus for the manufacture of products, so that the marking of the products is carried out simultaneously with the exposure treatment of the products that are part of their manufacture.

Drawings

The invention is described below with reference to the accompanying drawings, in which:

FIG. 1 shows the principle of an apparatus for carrying out the method of the invention, and

fig. 2 shows an exemplary embodiment of the principle of a further device for carrying out the method according to the invention.

Detailed Description

In the drawings, like reference numerals designate corresponding elements.

In fig. 1, reference numeral 1 denotes a light source, and reference numeral 2 denotes a light beam thereof, which is directed to a photosensitive surface portion 5 of a circuit board 6 to be marked. In the light beam 2 of the light source 1 there are arranged an optical arrangement 3 and a device 4 with adjustable transparency. The device 4 comprises a region 41 in the propagation direction of the light and allowing light to pass, and a region 42 which does not allow light to pass or whose transparency is substantially lower than that of the region 41.

The shape and position of the areas 41 and 42 are chosen such that a pattern corresponding to the desired marking can be formed on the photosensitive surface 5 of the circuit board 6 by means of them. The figures do not show means for adjusting the shape and/or position of the zones 41 and 42. In a preferred embodiment of the invention, the devices 4 and the areas 41 and 42 in them are controlled so that the light of the pattern formed by the areas 41 and 42 forms the desired marking, for example a one-dimensional code such as a bar code, a two-dimensional (2D) code or other desired marking, on the light-sensitive surface of the circuit board 6. Light passing through the transparent region 41 of the device 4 exposes a region 51 on the photosensitive surface. No light can shine through the area 42 of the device 4 onto the surface 5, the area 52 remaining unexposed. In this way, a pattern consisting of exposed and unexposed areas and corresponding to a desired mark is formed on the surface of the circuit board 6, which pattern becomes a permanent pattern on the surface of the circuit board in the manufacturing process of the circuit board.

Figure 2 shows the principle of another preferred embodiment for implementing the method of the invention. In this example, reference numeral 1 denotes a light source, the light beam 2 of which is directed towards the light-sensitive surface 5 of the circuit board 6. Means 4 with adjustable transparency are arranged in the light beam, and optical means 3, such as one or more lenses, between these means 4 and the light source 1, for directing the light beam to the means 4. Between the device 4 and the circuit board 6 to be marked a second optical means 7 is arranged, preferably the means 7 is for example one or more lenses, by means of which optical means 7 light passing through the device 4 can be directed to the light-sensitive surface 5 of the circuit board 6, so that the pattern formed on the surface 5 is preferably a reduced pattern of the pattern formed by the device 4 for example. The transparent area 41 is formed, for example, by means of the optical means 7, as an illuminated area 51 on the surface 5, the size of which area is smaller than the area 41. The optical means 3 and 7 may also be mirrors, optical fibres or fibre bundles, by means of which the light beam of the light source is directed towards the means 4 and the light passing through the means 4 is further directed towards the light-sensitive surface 5.

As light source 1 several light sources can be used, such as incandescent, fluorescent or discharge lamps, LED light sources, lasers, or other suitable radiation sources. The spectrum of the light or radiation emitted by the light source 1 or the radiation source 1 is chosen such that it can be used for exposing a photosensitive or radiation-sensitive coating 5 formed on the surface of the circuit board 6. Accordingly, the device 4 is selected such that the area 41 therein allows radiation from the radiation source 1 to pass through them, and an area 42 may be formed in the device 4 which serves to prevent radiation from the radiation source 1 from passing completely through it, or the amount of radiation from the radiation source 1 which is allowed to pass through the area 42 is substantially smaller than the amount of radiation which is allowed to pass through the area 41.

The means 4 for directing light towards the object can also consist of micro-mirrors, the angle of each individual mirror with respect to the radiation 2 from the light source 1 can be individually varied so that light is projected onto the photosensitive surface 5, thereby forming the illuminated area 51, or light is not projected onto the photosensitive surface 5, the area 52 remaining unexposed.

In one embodiment of the present invention, the same light source as that used for manufacturing the circuit board in the manufacturing process of the circuit board 6 is used as the light source 1.

Claims (7)

1. A method of distinctively marking electronic components in the manufacture of electronic components, the method comprising the steps of: -exposing on each circuit-board blank the photosensitive surface required for manufacturing the blank to form a machine-readable pattern, characterized in that said exposure is carried out by selectively forming exposed and non-exposed areas on said photosensitive surface using adjustable means, and subsequently using said pattern in the manufacture of the product itself to distinguish said blanks from each other.

2. A method according to claim 1, characterized in that the pattern is a two-dimensional code.

3. The method of claim 1, wherein the graphic is a bar code.

4. A method according to claim 1, characterized in that the graphic is an alphanumeric graphic.

5. Method according to any of claims 1-4, characterized in that the adjustable means are micro mirrors which project light onto the photosensitive surface and change the projection angle separately, thereby forming exposed and non-exposed areas on the photosensitive surface.

6. A method according to any of claims 1-4, characterized in that said adjustable means is a liquid crystal display panel, the transparency of the respective areas of which is selectively adjusted, thereby forming exposed and non-exposed areas on said photosensitive surface.

7. A method according to any of claims 1-4, characterized in that said adjustable means are optical fibres, and that the control is performed such that light is shone onto said light-sensitive surface through a selected part of the optical fibres, so that an exposed area and a non-exposed area are formed on said light-sensitive surface.