WO2025168788A1 - A dispensing device arranged for dispensing solder paste as well as a corresponding solder dot dispensing device and a related method - Google Patents

Abstract

A dispensing device arranged for dispensing solder paste, said dispensing device comprising a dispensing reservoir arranged for containing said solder paste, a channel arranged for receiving, at an inlet thereof, said solder paste from said dispensing reservoir and for dispensing said solder paste at an outlet thereof, an elongated sealing element positioned in said channel, a buffer chamber arranged for buffering solder paste, wherein said buffer chamber is connected to said channel, wherein said elongated sealing element is arranged to provide a passageway between said dispensing reservoir and said buffer chamber in a closed state and arranged to provide a passageway between said buffer chamber and said outlet of said channel in an opened state.

Description

Title

A dispensing device arranged for dispensing solder paste as well as a corresponding solder dot dispensing device and a related method.

Technical field

The present disclosure generally relates to the field of dispensing and, more specifically, to dispensing devices arranged for dispensing solder paste onto a work piece.

Background

Semiconductor packaging relies heavily on precise and controlled application of solder paste onto designated components such as lead frames, dies, and substrates. Among the commonly employed tools for this task is the Time- Pressure, TP, dispensing valve, a device integral to the semiconductor assembly process. This apparatus operates with a syringe filled with viscous solder paste, featuring a piston at its end and connected to a controller outlet, allowing the controlled release of compressed air pulses into the syringe barrel.

In the OFF state, the TP dispensing valve remains inactive, withholding compressed air from the syringe. At this point, the spool within the valve rests in the "down" position, effectively halting the flow of solder paste. Transitioning to the ON state involves the elevation of the spool to the "up" position, coupled with the concurrent application of compressed air to the piston by the controller. This process exerts pressure on the solder paste within the syringe, facilitating its controlled dispensing onto the target object.

The fluid dynamics of solder paste within the TP dispensing valve can be modelled as viscous laminar pipe flow, justified by the low Reynolds Number, indicative of laminar flow characteristics. In mass production settings, a purging step is introduced to eliminate outdated solder paste and potential entrapped air or gas before continuous dispensing. This ensures that the flow is approximately fully developed. The typical round cross-section of flow channels within the control volume further confirms the characterization of the flow as pipe flow.

The dispensing volume, denoted as V, representing the dispensing dot size, for viscous laminar pipe flow can be expressed mathematically. It incorporates variables such as pipe radius (r), flow distance (L), relative pressure along the flow pathway (Ap), dispensing valve-on time (t), and solder paste viscosity indexes (K, n). The constants of pipe radius (r) and flow distance (L) within a given control volume remain constant, contributing to the consistency of solder dispensing dot size.

Variables such as solder paste viscosity indexes (K, n), relative pressure along the flow pathway (Ap), and dispensing valve-on time (t) are critical determinants of uniformity in solder dispensing dot size. To maintain consistent dispensing dot sizes during mass production, it becomes imperative to uphold the stability of solder paste viscosity, ensuring a steady relative pressure, and precise timing for valve opening. Any deviation from these parameters can lead to quality issues, as depicted in the illustration of inconsistent dispensing dot sizes on the TP dispensing platform.

The Time-Pressure dispensing valve plays a role in semiconductor packaging by providing a controlled mechanism for the application of solder paste. The underlying fluid dynamics, characterized as viscous laminar pipe flow, necessitate strict adherence to parameters such as solder paste viscosity, relative pressure, and valve-on time to ensure consistent dispensing dot sizes. Deviations from these parameters can compromise the quality and reliability of the semiconductor assembly process, highlighting the critical role of precision and control in this intricate manufacturing domain.

Summary

It would be advantageous to achieve a dispensing device that is better able to ensure consistent dispensing dot sizes compared to the prior art. It would further be advantageous to achieve a corresponding solder dot dispensing device and related methods.

In a first aspect of the present disclosure, there is provided a dispensing device arranged for dispensing solder paste, said dispensing device comprising: a dispensing reservoir arranged for containing said solder paste; a channel arranged for receiving, at an inlet thereof, said solder paste from said dispensing reservoir and for dispensing said solder paste at an outlet thereof; an elongated sealing element positioned in said channel; a buffer chamber arranged for buffering solder paste, wherein said buffer chamber is connected to said channel; wherein said elongated sealing element is arranged to provide a passageway between said dispensing reservoir and said buffer chamber in a closed state and arranged to provide a passageway between said buffer chamber and said outlet of said channel in an opened state.

The inventors have found that, in prior art solutions, the reliability of maintaining a consistent dispensing dot size in semiconductor packaging hinges on two factors: the stability of the compressed air source and the precision of the solenoid valve in the controller.

Despite the implementation of a high-quality compressed air source and a top-notch solenoid valve, the challenge of achieving uniform dispense dot sizes persists, primarily due to the time-dependent shear-thinning non-Newtonian nature of solder pastes.

Solder pastes exhibit a material property characterized by shearthinning, meaning their viscosity decreases with increased shear rate over time. This non-Newtonian behaviour poses a significant hurdle to sustaining stable viscosity in the long term. Even with optimal conditions from the compressed air source and solenoid valve, the inherent nature of solder pastes makes it challenging to ensure viscosity consistency throughout mass production.

The inventors have found that it may be beneficial to incorporate a buffer chamber into the dispensing device. The buffer chamber may be designed such that it can buffer a particular volume. The volume of solder paste that it can buffer may equal the required, or desired, solder dot at the work piece.

As such, the solder paste will no longer be directly dispensed from the dispensing reservoir directly to the work piece. The solder paste in the dispensing reservoir is first guided to the buffer chamber. The dispensing then entails emptying the buffer chamber. The above described desire is accomplished by the elongated sealing element that is positioned in the channel. The elongated sealing element can take two different positions.

In a closed position, the elongated sealing element is arranged to provide a passageway between the dispensing reservoir and the buffer chamber. The outlet of the channel is then closed. This would result in solder paste to be guided from the dispensing reservoir to the buffer chamber. As such, the buffer chamber is filled with solder paste.

In an open position, the elongated sealing element is arranged to provide for a passageway between the buffer chamber and the outlet of the channel. In other words, the solder paste present in the buffer chamber is dispensed via the outlet of the channel onto the workpiece. In the open position, the passageway between the dispensing reservoir and the buffer chamber is closed. Of course, there is also no passageway, in this position, directly between the dispensing reservoir and the outlet of the channel.

The effect is that the dispensing process is made in two steps. In a first step, the buffer chamber is filled with solder paste. In a second step, the buffer chamber is empties, i.e. dispensed, via the outlet of the channel onto the work piece.

One of the advantageous of the above described process is that the total amount of volume that is being dispensed can much better be controlled. The volume of solder paste that is being dispensed then relates to the volume of the buffer chamber.

This would make the process not reliant on viscosity, or pressures, or anything alike.

In an example, the elongated sealing element comprises: a first seal at a first end of said sealing element; a second seal at a second end, opposite to said first end, of said sealing element, wherein, in said closed state, said second seal is arranged to seal said output of said channel, and wherein, in said opened state, said first seal is arranged to seal said inlet of said channel. The elongated sealing element may, for example, be a spool. The spool comprises, at a first end thereof, a first seal and comprises, at a second end thereof, a second seal.

The spool may be able to move laterally along in the channel. Moving to one side of the channel, for example, the closed state, the second seal will seal the output of the channel. This will accomplish that no solder paste can be dispensed from the dispensing device. In this state, there is passageway between the dispensing reservoir and the buffer chamber, to push the solder paste from the dispensing reservoir to the buffer chamber. As such, in this closed state, the first seal will not seal the input of the channel.

In the opened state, a passageway is provided between the buffer chamber and the outlet of the channel. In other words, the solder paste present in the buffer chamber can be released via the output of the channel onto the work piece. In the opened state, the first seal will close, i.e. seal, the input of the channel such that the solder paste in the dispensing reservoir is not able to flow to the buffer chamber and not able to flow to the output of the channel.

In a further example, the buffer chamber comprises: a buffer piston arranged for pushing buffered solder paste towards said outlet of said channel, wherein said buffer piston is moveable between a buffered position and a dispensed position, wherein in said dispensed position buffered solder paste has been dispensed to said outlet of said channel, and wherein in said buffered position said buffer chamber has soldered paste buffered.

The buffer chamber in combination with the buffer may be viewed as a syringe. A syringe typically comprises a (cylindrical) barrel, i.e. the buffer chamber, a plunger, i.e. the buffer piston, and a dispensing tip or needle. The barrel holds the solder paste, while the plunger allows the controller to control the amount of material dispensed by pushing or pulling it within the barrel. The dispensing tip or needle plays a role in directing the flow of the solder paste towards the exit of the channel, ensuring precise application.

In a further example, the buffer chamber further comprises: a meter head arranged for physically providing a hard stop for said buffer piston in said buffer chamber, such that said meter head determines said relative location of said dispensed position in said buffer chamber. The term "meter head" is introduced as a component within the buffer chamber that serves a specific function. The meter head is designed to physically act as a hard stop for the buffer piston. In other words, it provides a mechanical barrier or limit to the movement of the buffer piston within the buffer chamber. This physical obstruction created by the meter head determines the relative location of the dispensed position within the buffer chamber.

The meter head plays a role in controlling the movement of the buffer piston, ensuring that it stops at the correct position to thereby determine a volume of the solder paste to be dispensed when needed. It serves as a mechanism to accurately measure and regulate the dispensing process, contributing to the precision and control of the solder paste application.

In a further example, the dispensing device further comprises a controller arranged for positioning said meter head in said buffer chamber.

The meter head may be controlled such that a particular relative position of the buffer position can be set. In essence, the position of the buffer piston effectively determine the volume of the solder paste to be dispensed.

The buffer piston may thus elevate, based on solder paste being injected from the dispensing reservoir into the buffer chamber via the channel, until it touches the meter head and cannot move any further.

In another example, the controller is arranged for positioning said meter head based on a volume to be dispensed by said dispensing device.

In a further example, the cross-section of a part of said channel remains constant, wherein said first seal is dimensioned such that a cross-section of said first seal is larger than said cross-section of said part of said channel to thereby seal said channel by pressing said first seal onto a first end of said part of said channel; said second seal is dimensioned to fit inside said part of said channel to thereby seal said output of said channel.

In yet another example, the dispensing reservoir comprises a dispensing piston for pushing contained solder paste into said channel.

In a further example, the dispensing device further comprises: a compressed air device arranged for providing compressed air to any of said dispensing reservoir and said buffer chamber for moving said dispensing piston and buffer piston, respectively.

In an example, the dispensing device further comprises a controller for controlling said compressed air device.

The controller may, for example, be arranged to deliver compressed air to the dispensing reservoir whenever solder paste is to be channelled from the dispensing reservoir to the buffer chamber. This is to be performed in the so-called closed position of the elongated sealing member.

The controller may, for example ,be arranged to deliver compressed air to the buffer chamber whenever solder paste is to be channelled from the buffer chamber to the workpiece, via the outlet of the channel. This is to be performed in the so-called dispensing position of the elongated sealing member.

The controller may deliver pulses of compressed air to at least one of the dispensing reservoir and the buffer chamber.

In a second aspect of the present disclosure, there is provided a method of dispensing solder paste using a dispensing device in accordance with any of the previous examples, wherein said dispensing device comprises a controller, said method comprises the steps of: controlling, by said controller, said elongated sealing element between said closed state and said opened state.

It is noted that the advantages as explained with reference to the first aspect of the present disclosure, being the dispensing device for dispensing solder paste, are also applicable to the second aspect of the present disclosure, being the method of dispensing solder paste.

In an example here, the step of controlling comprises: positioning, by said controller, said meter head for setting a dispensing volume.

In another example, the dispensing reservoir comprises a dispensing piston for pushing contained solder paste into said channel, and wherein said dispensing device further comprises a compressed air device arranged for providing compressed air to any of said dispensing reservoir and said buffer chamber for moving said dispensing piston and buffer piston, respectively, wherein said method comprises the step of: controlling, by said controller, said compressed air device.

In a third aspect of the present disclosure, there is provided a solder dot dispensing device comprising for dispensing solder on a work piece, said solder dot dispensing device comprising a dispensing device in accordance with any of the examples as provided above.

The work piece may be a lead frame, a die, and a substrate. Another example of a work piece is the Printed Circuit Board, PCB, where solder dots are dispensed at precise locations to fix electronic elements like resistors, capacitors, and integrated circuits.

Solder dot dispensing may find application in the assembly of Microelectromechanical Systems, MEMS, involving intricate mechanical components on semiconductor substrates. Electronic components, such as connectors, switches, and sensors, may also serve as work pieces requiring the accurate placement of solder dots for effective attachment. Light Emitting Diode, LED, modules represent another category, with solder dots being dispensed to secure LEDs to the substrate and establish essential electrical connections.

Additionally, solder dot dispensing may be relevant in the assembly of Flexible Printed Circuits, FPC, where the dots contribute to establishing electrical connections on bendable substrates. Beyond electronics, this technology may extend to automotive applications, assisting in the assembly of electronic components within automotive systems, including control units and sensors.

In a fourth aspect of the present disclosure, there is provided a computer program product comprising a computer readable medium having instructions stored thereon which, when executed by a dispensing device cause said dispensing device to implement a method in accordance with any of the examples as provided above.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter.

Brief description of the drawings

Fig. 1 discloses a schematic diagram of a prior art Time-Pressure, TP, dispensing device in an Off-state;

Fig. 2 discloses a schematic diagram of a prior art TP dispensing device in an On-state;

Fig. 3 disclose a schematic illustrating factors affecting the solder dispensing dot size in TP dispensing;

Fig. 4 discloses an initial state of a dispensing device in accordance with the present disclosure;

Fig. 5 discloses a refill state of a dispensing device in accordance with the present disclosure;

Fig. 6 discloses a dispensing state of a dispensing device in accordance with the present disclosure.

Detailed description

It is noted that in the description of the figures, same reference numerals refer to the same of similar components performing a same of essentially similar function.

A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings. The ensuing description above provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or" in reference to a list of two or more items, covers all the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

These and other changes can be made to the technology considering the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

Figure 1 discloses a schematic diagram 1 of a prior art Time-Pressure, TP, dispensing device in an Off-state and figure 2 discloses a schematic diagram 2 of a prior art TP dispensing device in an On-state.

In semiconductor packaging, the time-pressure, TP, dispensing valve, depicted in Fig.1 , is a frequently utilized apparatus for applying viscous solder pastes onto target objects like lead frames, dies, and substrates.

The solder paste 5 is typically contained within a syringe 3 equipped with a piston 4 positioned at its end. The syringe barrel is linked to the controller's outlet, allowing the controller to deliver pulses of compressed air 6 to the syringe barrel.

In the OFF state of the TP dispensing valve, the controller refrains from delivering compressed air to the syringe barrel. The spool 7 remains in the "down" position, thus stopping the flow of solder paste from the valve. When the TP dispensing valve is in the ON state, the spool 7 is elevated to the "up" position, the controller concurrently applies compressed air to the piston, exerting pressure on the solder paste within the syringe and thus squeezing the solder paste out.

The general fluid flow of solder paste within the TP dispensing valve can be approximated as viscous laminar pipe flow. This approximation is based on the remarkably low Reynolds Number (<<2100), indicating laminar flow characteristics.

In mass production, a purging step is employed to remove outdated solder paste and potential entrapped air/gas before continuous dispensing, ensuring an approximately fully developed flow. The typical round cross-section of flow channels within the specified control volume indicates the characterization of the flow as pipe flow. The dispensing volume V, i.e. the dispensing dot size, for viscous laminar pipe flow can be expressed as, Where r is the pipe radius, L is flow distance, Ap is relative pressure along the flow pathway, t is dispensing valve-on time, and K and n are solder paste viscosity indexes.

As depicted in Figure 3, and indicated with reference numeral 101 , the constants of pipe radius (r) and flow distance (L) within a given control volume remain unchanged, thereby not influencing the consistency of solder dispensing dot size. The variables that do impact the uniformity of solder dispensing dot size encompass solder paste viscosity indexes (K, n), the relative pressure along the flow pathway (Ap), and the dispensing valve-on time (t).

To ensure consistent dispensing dot sizes during mass production, it may be of importance to uphold the stability of solder paste viscosity, maintain a steady relative pressure, and ensure accurate timing for valve opening. Failure to do so can result in a quality issue of inconsistent dispensing dot sizes on TP dispensing platform.

The maintenance of a steady relative pressure and accurate timing for valve opening may rely on the stability of the compressed air source and the performance of the solenoid valve in the controller, respectively.

Even with a high-quality compressed air source and a superior solenoid valve, achieving consistent dispense dot sizes during mass production remains challenging due to the time-dependent shear-thinning non-Newtonian material property of solder pastes. This material characteristic may make it difficult to maintain a stable viscosity over the long term with solder pastes.

In Figures 4, 5 and 6, schematic diagrams 201 , 202, 203 illustrate the structure and process steps of the invented dispensing valve aimed at improving solder dot dispensing, as per the present disclosure.

The approach involves incorporating an additional buffer chamber 204 design to achieve consistent solder dot dispensing. The dispensing valve comprises a valve body 205, a spool 206, a micrometer head 207, and a buffer piston 208 within the buffer chamber 204.

Connecting a syringe filled with solder paste to the fluid inlet port of the valve body is facilitated by a connector, such as a luer.

The distinctive aspect of the present disclosure lies in the incorporation of an extra buffer chamber within the valve body. Positioned on the side of the main valve body, this buffer chamber is linked to the flow channel of the main valve body. Prior to initiating continuous solder paste dispensing, a purging step may be performed to eliminate obsolete solder paste and address any potential entrapment of air or gas. In the initial state after purging, as shown in figure 4, no compressed air is applied to the piston in the dispensing reservoir. Compressed air is applied to fill the buffer chamber, thereby pressing the piston in the buffer chamber to the bottom. Consequently, the initial status indicates the absence of solder paste within the buffer chamber.

The spool may be characterized by a long, slender, round shaft featuring two protrusions. The large protrusion situated in the upper position, i.e. the first seal, may serve the purpose of regulating the on/off status for the inflow of solder paste from the dispensing reservoir to the buffer chamber I outlet.

The small protrusion located in the lower position, i.e. the second seal, of the spool is employed to govern the on/off status for the outflow of solder paste. In the initial state after purging, as shown in Figure 4, the spool is released at the "down" position, and the large protrusion of the spool makes mechanical contact with the lower surface of the inlet chamber, thereby hindering the flow of solder paste from the dispensing reservoir into the valve body. For the solder paste remaining in the valve body, the viscous material property of solder paste prevents it from dripping out of the valve body.

In step 2, as shown in figure 5, the process step involves refilling the buffer chamber with solder paste. The spool is raised until the large protrusion establishes mechanical contact with the top surface of the inlet chamber. This action causes the associated small protrusion to close the flow-out channel. Compressed air is applied to the syringe barrel's piston, which is simultaneously disconnected from the buffer chamber.

The resulting pressure difference propels the solder paste in the dispensing reservoir, causing it to flow into the buffer chamber and elevate the buffer chamber's piston until it touches the micrometer head.

In step 3, as shown in figure 6, the process involves expelling the refilled solder paste from the buffer chamber through dot dispensing. The spool is released to the "down" position to halt the solder paste flow from the syringe into the valve body, while the downward movement of the associated small protrusion opens the flow-out channel. Upon disconnecting compressed air from the syringe barrel's piston, it is simultaneously connected to the buffer chamber. The compressed air within the buffer chamber exerts pressure on the buffer chamber's piston, causing it to descend, and the piston extrudes the solder paste through the valve body's outlet. The dispensing of solder paste ceases until the buffer chamber's piston reaches the bottom of the buffer chamber.

In each dispensing cycle within the particular disclosure, there are three steps: initial status, refilling the buffer chamber with solder paste, and dispensing solder paste dots until returning to the Initial status. The dispensing dot size is determined by the cross-sectional area of the buffer chamber multiplied by the refilled height 'h'. A user may customize the dot dispensing size by manually adjusting the micrometer head, or by using a controller for controlling the micrometer, before dispensing, thereby modifying the refilled height 'h'. Both the cross-sectional area of the buffer chamber and the refilled height 'h' remain constant during dispensing. The present disclosure mayensure a direct correlation between the solder dispensing dot size and the two constants, eliminating uncontrollable variables and guaranteeing consistent user-defined solder dispensing dot size.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The provided figures and descriptions of the embodiments of the invention are illustrative and explanatory to the heart of the invention and should not be seen as limiting the invention thereto. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

1. A dispensing device arranged for dispensing solder paste, said dispensing device comprising: a dispensing reservoir arranged for containing said solder paste; a channel arranged for receiving, at an inlet thereof, said solder paste from said dispensing reservoir and for dispensing said solder paste at an outlet thereof; an elongated sealing element positioned in said channel; a buffer chamber arranged for buffering solder paste, wherein said buffer chamber is connected to said channel; wherein said elongated sealing element is arranged to provide a passageway between said dispensing reservoir and said buffer chamber in a closed state and arranged to provide a passageway between said buffer chamber and said outlet of said channel in an opened state.

2. A dispensing device in accordance with claim 1 , wherein said elongated sealing element comprises: a first seal at a first end of said sealing element; a second seal at a second end, opposite to said first end, of said sealing element, wherein, in said closed state, said second seal is arranged to seal said output of said channel, and wherein, in said opened state, said first seal is arranged to seal said inlet of said channel.

3. A dispensing device in accordance with any of the previous claims, wherein said buffer chamber comprises: a buffer piston arranged for pushing buffered solder paste towards said outlet of said channel, wherein said buffer piston is moveable between a buffered position and a dispensed position, wherein in said dispensed position buffered solder paste has been dispensed to said outlet of said channel, and wherein in said buffered position said buffer chamber has soldered paste buffered.

4. A dispensing device in accordance with claim 3, wherein said buffer chamber further comprises: a meter head arranged for physically providing a hard stop for said buffer piston in said buffer chamber, such that said meter head determines said relative location of said dispensed position in said buffer chamber.

5. A dispensing device in accordance with claim 4, wherein said dispensing device further comprises a controller arranged for positioning said meter head in said buffer chamber.

6. A dispensing device in accordance with claim 5, wherein said controller is arranged for positioning said meter head based on a volume to be dispensed by said dispensing device.

7. A dispensing device in accordance with any of the previous claims and at least to claim 2, wherein a cross-section of a part of said channel remains constant, wherein said first seal is dimensioned such that a cross-section of said first seal is larger than said cross-section of said part of said channel to thereby seal said channel by pressing said first seal onto a first end of said part of said channel; said second seal is dimensioned to fit inside said part of said channel to thereby seal said output of said channel.

8. A dispensing device in accordance with any of the previous claims, wherein said dispensing reservoir comprises a dispensing piston for pushing contained solder paste into said channel.

9. A dispensing device in accordance with claim 8, wherein said dispensing device further comprises: a compressed air device arranged for providing compressed air to any of said dispensing reservoir and said buffer chamber for moving said dispensing piston and buffer piston, respectively.

10. A dispensing device in accordance with claim 9, wherein said dispensing device further comprises a controller for controlling said compressed air device.

11. A method of dispensing solder paste using a dispensing device in accordance with any of the previous claims, wherein said dispensing device comprises a controller, said method comprises the steps of: controlling, by said controller, said elongated sealing element between said closed state and said opened state.

12. A method in accordance with claim 11 , and claim 4, wherein said step of controlling comprises: positioning, by said controller, said meter head for setting a dispensing volume.

13. A method in accordance with any of the claims 11 - 12, wherein said dispensing reservoir comprises a dispensing piston for pushing contained solder paste into said channel, and wherein said dispensing device further comprises a compressed air device arranged for providing compressed air to any of said dispensing reservoir and said buffer chamber for moving said dispensing piston and buffer piston, respectively, wherein said method comprises the step of: controlling, by said controller, said compressed air device.

14. A solder dot dispensing device comprising for dispensing solder on a work piece, said solder dot dispensing device comprising a dispensing device in accordance with any of the claims 1 - 8.

15. A computer program product comprising a computer readable medium having instructions stored thereon which, when executed by a dispensing device cause said dispensing device to implement a method in accordance with any of the claims 9