METHOD AND DEVICE FOR APPLYING SOLDER PASTE FLUX

Abstract

A method of applying viscous media on a substrate is disclosed. In the method, the substrate is provided, which is arranged for mounting of electronic components thereon. Further, flux is provided on a deposit of solder paste, which deposit is arranged at a predetermined position on the substrate. The flux is provided by a non-contact dispensing process, such as jetting. By providing flux on the deposit prior to reflow, the risk of quality related issues, such as e.g. graping, advantageously is reduced.

Claims

1. A method of applying viscous media on a substrate, the method comprising: arranging the substrate for mounting of electronic components thereon; and providing flux on densely packed deposits of solder paste, which deposit is arranged at a certain position on the substrate; wherein the flux does not contain any metal particles and is provided by a non-contact dispensing process on top of the small deposits in order to partly or fully cover the deposits prior to reflow without diluting the solder paste deposits, i.e. without increasing concentration of the flux to adversely affect quality of the solder paste deposits, so that at least a part of the flux of said cover may evaporate prior to reflow oxidation and/or is consumed during reflow oxidation instead of part of the flux of the solder paste, thereby reducing risk that a lack or insufficient amount of flux during reflow oxidation may give rise to unreflowed solder particles and/or dry joints without increasing the risk of short-circuiting or bridging of densely packed smaller electronic components mounted on said deposits.

2. The method according to claim 1, wherein at least a part of the flux is provided on at least a part of an electronic component attached to the deposit.

3. The method according to claim 1, further comprising attaching an electronic component to the deposit after providing the flux on said deposit.

4. The method according to claim 1, wherein the deposit of solder paste is a screen-printed deposit of solder paste.

5. The method according to claim 1, wherein the deposit of solder paste is a non-contact dispensed deposit of solder paste.

6. The method according to claim 1, further comprising forming the deposit of solder paste by providing a predetermined amount of solder paste to a predetermined position on the substrate according to a printing job or program.

7. The method according to claim 1, wherein the providing of flux is performed by adding a predetermined amount of flux to a predetermined position of the substrate.

8. The method according to claim 1, wherein the deposit of solder paste is formed by means of a first jetting head assembly and the flux is provided by means of a second non-contact dispensing head assembly (e.g. a jetting head assembly), and wherein the first jetting head assembly and the second non-contact dispensing head assembly are different.

9. The method according to claim 8, wherein the first jetting head assembly and the second non-contact dispensing head assembly (e.g. a jetting head assembly) each forms part of a single equipment device.

10. The method according to claim 8, wherein the first jetting head assembly and the second non-contact dispensing head assembly (e.g. a jetting head assembly) each forms part of two separate and/or different equipment devices.

11. The method according to claim 1, wherein the amount of flux provided on the deposit is based on a volume of said deposit.

12. The method according to claim 1, further comprising: inspecting the deposit prior to providing the flux; estimating a volume of the deposit based on the inspection; and in response to the estimated volume, providing flux on the deposit.

13. The method according to claim 12, wherein the flux is provided based on the inspecting the deposit and in response to the estimated volume being below a threshold value.

14. The method according to claim 1, further comprising heating the substrate so as to reflow the solder paste of the deposit.

15. The method according to claim 12, further comprising forming the deposit of flux by adding a predetermined amount of flux to a predetermined position according to a printing job or program created in response to the inspecting of the deposit of solder paste prior to providing the flux.

16. The method according claim 1, further comprising: identifying a sub-range of the solder paste deposits containing low deposit volumes, e.g. below a certain threshold amount, and, accordingly, small amounts of flux; and providing additional amounts of flux on the identified subrange of the solder paste deposits having low deposit volumes, wherein the provision of the additional amounts of flux on said identified subrange of the solder paste deposits having low deposit volumes is performed in order to reduce the risk for a shortage or lack of solder paste during reflow oxidation without increasing the risk of short-circuiting or bridging of densely packed smaller electronic components mounted on said deposits.

17. A jetting device for applying viscous medium on a substrate, the device comprising at least one non-contact dispensing head assembly configured to provide flux on densely packed deposits of solder paste containing metal particles, which deposits are arranged at certain positions on the substrate, said jetting device comprises a jetting head assembly and a non contact dispensing head assembly, wherein the jetting head assembly is configured to form jetted deposits of solder paste containing metal particles on predetermined positions on the substrate and the non-contact dispensing head assembly is configured to provide flux not containing metal particles on said deposits, wherein densely packed deposits of solder paste are applied by the jetting head assembly, and wherein the at least one non-contact dispensing head assembly is configured to apply additional flux that does not contain any metal particles on top of the deposits in order to partly or fully cover the deposit prior to reflow without diluting the solder paste deposits, i.e. without increasing flux concentration to adversely affect quality of the solder paste deposits, so that at least a part of the additional flux of said cover may evaporate prior to reflow oxidation and/or is consumed during reflow oxidation instead of part of the flux of the solder paste, said device of combined jetting head assembly and non-contact dispenser head assembly being configured to provide different types of viscous medium on the same substrate is thereby configured to provide for densely packed solder deposits after reflow oxidation without reducing risk that a lack or insufficient amount of flux during reflow oxidation may give rise to unreflowed solder particles and/or dry joints and without increasing the risk of short-circuiting or bridging of densely packed smaller electronic components mounted on said deposits, wherein said non-contact dispensing head assembly is configured so that the additional flux is added in a non-contact process where the additional flux is not simultaneously in contact with both the nozzle and the deposit during application, thereby reducing the risk that the deposits adhere to the added flux.

18. The jetting device according to claim 17, configured to provide at least a part of the flux on at least a part of an electronic component attached to the deposit of solder paste.

19. The jetting device according to claim 17, further comprising an inspection means configured to inspect the deposit and/or the flux.

20. The jetting device according to claim 19, further comprising forming the deposit of flux by adding a predetermined amount of flux to a predetermined position according to a printing job or program created in response to inspecting the deposit of solder paste prior to providing the flux.

21. The jetting device of claim 17, said device is further configured to identify a sub-range of the solder paste deposits having low deposit volumes (e.g. below a certain threshold amount) and, accordingly, small amounts of flux; and providing additional amounts of flux on the identified sub-range of the solder paste deposits having low deposit volumes.

22. A screen printer device for applying viscous medium on a substrate, the device further comprising at least one integrated non-contact dispensing head assembly configured to provide flux on densely packed deposits of solder paste, which deposit is arranged at a certain position on the substrate, said screen printer is configured to screen print deposits of solder paste on predetermined positions on the substrate and the integrated non-contact dispensing head assembly is configured to provide flux on said deposits, wherein densely packed deposits of solder paste are provided on the substrate by the screen printer, and wherein the at least one non-contact dispensing head assembly is configured to apply additional flux that does not contain any metal particles on top of the deposits in order to partly or fully cover the deposits prior to reflow without diluting the solder paste deposits, i.e. without increasing flux concentration to adversely affect quality of the solder paste deposits, so that at least a part of the additional flux of said cover may evaporate prior to reflow oxidation and/or is consumed during reflow oxidation instead of part of the flux of the solder paste, said combination of screen printer and non-contact dispenser configured to provide different types of viscous medium on the same substrate is thereby configured to provide for densely packed solder paste deposits on the substrate after reflow oxidation without reducing the risk that a lack or insufficient amount of flux during reflow oxidation may give rise to unreflowed solder particles and/or dry joints and without increasing risk of short-circuiting or bridging of densely packed smaller electronic components mounted on said deposits, wherein said non-contact dispensing head assembly is configured so that the additional flux is added in a non-contact process where the additional flux is not simultaneously in contact with both the nozzle and the deposit during application, thereby reducing the risk that the deposits adhere to the added flux.

23. The screen printer device of claim 22, further comprising an inspection means configured to inspect the deposits of solder paste prior to applying the additional flux on the deposits.

24. The screen printer device of claim 23, wherein the flux is provided based on inspecting the deposit and in response to estimated volume of the deposit being below a threshold value.

25. The screen printer device of claim 21, said device is further configured to identify a sub-range of the solder paste deposits having low deposit volumes (e.g. below a certain threshold amount) and, accordingly, small amounts of flux; and providing additional amounts of flux on the identified sub-range of solder paste deposits having low deposit volumes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] These and other aspects will now be described in more detail with reference to the appended drawings showing embodiments.

[0060] FIGS. 1-3 are block diagrams illustrating arrangements according to embodiments of the present invention;

[0061] FIGS. 4-6 illustrate in flow chart form embodiments of the present invention;

[0062] FIG. 7 is a perspective view showing a general outline of a jetting device according to an embodiment;

[0063] FIG. 8 is a schematic view showing a cut away portion of a jetting head assembly according to an embodiment; and

[0064] FIGS. 9a-c and 10 illustrate electronic components attached to the deposits according to embodiments of the present invention.

[0065] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted or merely suggested. Like reference numerals refer to like elements throughout the description.

DETAILED DESCRIPTION

[0066] The present aspects will now be described more fully hereinafter with reference to the accompanying drawing, in which currently preferred embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present aspects to the skilled person.

[0067] Turning first to FIGS. 1 and 4, there is shown a first exemplary embodiment of the present invention. A substrate, such as a PCB 100 is transferred 400 to a jet printing device 112 for solder paste, where a plurality of deposits are formed 402 at predetermined positions of the PCB 100. Then, the PCB 100 is transferred 404 to a non-contact dispensing device116 for flux, where predetermined amounts of flux are provided 406 on at least some of the deposits. Following the non-contact dispensing 406 of the flux, the substrate 100 is transferred 408 to a component mounting device 118, where electrical components are mounted 410 on the substrate 100. As an alternative, there may be included a step of inspecting the final results of the solder paste jetting and the non-contact dispensing of flux. After the mounting 410 of the electronic components, the substrate is transferred 412 to a reflow oven 119 where the deposits are reflowed 414 in order to form solder joints.

[0068] With reference now to FIGS. 2 and 5, there is shown another exemplary embodiment of the present invention. According to this embodiment, the substrate 100 is transferred 500 to a screen printer 110 which applies 502 the solder paste forming the deposits. The substrate 100 is then transferred 504 to an inspection device 114 that inspects 506 the deposits. The results of the inspection 506 is recorded and relayed to the non-contact dispensing device 116 for flux. With the information as to the results of the inspection, the non-contact dispensing device 116 for flux can perform any required non-contact dispensing 510 of flux onto deposits e.g. having a volume being below a pre-determined threshold value. Further, the non-contact dispensing device 116 for flux may comprise a jetting head assembly for solder paste, and may hence be able to correct deficiencies of the deposits by adding additional amounts of solder paste to specific deposits or locations on the substrate 100. The inspection device 114 is preferably incorporated in the same machine as the non-contact dispensing device 116 for flux, thus forming a combined inspection and jetting device 115. However, the inspection device 114 can also be a separate machine.

[0069] Following the application 510 of the flux, the substrate 100 is transferred 512 to the component mounting device 118, where the electronic components are mounted 514 by attaching them to the deposits. Finally, the substrate 100 is transferred 516 to the reflow oven 119 at which the deposits are reflowed 518.

[0070] The block diagram of FIG. 3 and the flow chart of FIG. 6 illustrate yet another exemplary embodiment of the present invention. Here, the jetting device 112 for solder paste, the component mounting device 118 and the non-contact dispensing device 116 for flux are incorporated in a combined device 200. Following the transfer 600 of the substrate 100 to said device 200, deposits of solder paste are formed 602, electronic components mounted 604 and flux provided 606 on at least some of the deposits and on portions of electronic components attached to the deposits. The substrate 100 is then transferred 608 to the reflow oven for reflow 610 of the deposits.

[0071] Referring to FIG. 7, a non-contact dispensing device such as a jetting device 1 is illustrated which includes an X-beam 3 and an X-wagon 4 connected to the X-beam 3 via an X-rail 16 and reciprocally movable along the X-rail 16. The X-beam 3 is reciprocally and movably connected to a Y-rail 17, thereby being movable in directions perpendicular to the X-rail 16. The Y-rail 17 is rigidly mounted in the machine 1. Movement of the X-wagon 4 and the X-beam 3 may be driven by linear motors (not shown).

[0072] A conveyer 18 feeds a substrate 100 through the jetting device 1. When the substrate 100 is in the appropriate position under the X-wagon 4, a locking device 19 fixes the substrate 100 in place. A camera 7 locates fiducial markers on the surface of the substrate 100 to determine the precise position of the substrate 100. Viscous medium, such as solder paste and/or flux, is applied to the substrate 100 at desired or predetermined locations by moving the X-wagon 4 over the substrate 100 in a given, desired or predetermined pattern and operating a non-contact dispensing head assembly 14 such as a jetting head assembly at given, desired or predetermined locations.

[0073] Since production speed is a relatively important factor in the manufacturing of electronic circuit boards, the application of viscous medium is typically performed “on the fly”.

[0074] FIG. 8 illustrates example contents and function of parts enclosed in the non-contact dispensing head assembly 14 as described with reference to FIG. 7. The non-contact dispensing head assembly 14 includes an impacting device, such as a piezoelectric actuator 21 having a number of relatively thin, piezoelectric elements stacked together to form an actuator part 21a. A lower end of the actuator part 21a is rigidly connected to an assembly housing 15. The jetting head assembly 14 further includes a bushing 25, rigidly connected to the assembly housing 15, and a plunger 21b which is rigidly connected to a lower end of the actuator part 21a. The plunger 21b is axially movable while slidably extending through a bore in the bushing 25. Cup springs 24 are provided to resiliently balance the plunger 21b against the assembly housing 15, and to provide a preload for the actuator part 21a. An ejection control unit (not shown) applies a drive voltage intermittently to the piezoelectric actuator 21, thereby causing an intermittent extension thereof, and hence a reciprocating movement of the plunger 21b with respect to the assembly housing 15, in accordance with pattern printing data for the deposits.

[0075] The non-contact dispensing head assembly 14 further includes a plate-shaped or substantially plate-shaped jetting nozzle 26 operatively directed against the substrate 100, onto which relatively small droplets of viscous medium, such as solder paste or flux, are to be jetted. The jetting nozzle 26 comprises a through hole which defines a nozzle space 28, through which the viscous medium is forced during the jetting process. The viscous medium may be supplied to the nozzle by means of a pump assembly comprising a rotatable feeder screw 29 and a resilient feeder shell 33.

[0076] The plunger 21b includes a piston portion which is configured to slide and axially move through a piston bore 35. An impact end surface 38 of the piston portion of the plunger 21b is arranged relatively close to the nozzle 26. A jetting chamber 37 is defined by the end surface 38 of the plunger 21b, the cylindrical inner wall of the nozzle 26, the upper surface of the nozzle 26 and the upper end of the nozzle space 28. Thus, the jetting chamber 37 is connected to the upper portion of the nozzle space 28. Axial movement of the plunger 21b towards the nozzle 26 caused by the intermittent extension of the piezoelectric actuator 21 may result in a decrease (e.g., relatively rapid decrease) in the volume of the jetting chamber 37, and thus pressurisation (e.g., a rapid pressurisation) and jetting of the viscous medium in the nozzle space 28 through the nozzle 26.

[0077] The degree of filling of the nozzle space 28 before each jetting is set in order to obtain a controlled and individually adjusted amount of viscous medium in each droplet. The degree of filling may e.g. be adjusted by the rotational speed of the feeder screw 29.

[0078] FIGS. 9a-c illustrate an electronic component 910 that is mounted on a substrate, such as a PCB 900, e.g. by means of a pick-and-place machine (not shown). The electronic component 910 may e.g. be a 01005 component, having two contacting portions 912 that are attached to a respective deposit 920 of solder paste. In FIG. 9a, flux 930 has been provided on the solder paste deposits 920 after the electronic component 910 is attached to the deposits 920. The flux 930 may e.g. be provided in a relatively thin layer covering at least a part, or preferably all of, the deposits 920. In FIG. 9b, the flux 930 has been applied not only to the deposits 920 but also to a part of the electronic component 910. In this example, the flux is provided on a portion of the contact portion 912 of the electronic component 910. In FIG. 9c, flux 930 has been provided on both the deposits 920 and the electronic component 910 such that the deposits 920 and the electronic component 910 is fully covered by a layer of flux 930.

[0079] Alternatively, the electronic component 900 can be mounted after the flux 930 is provided. This is illustrated by FIG. 10, which shows an electronic component 910 wherein the contacting portions 912 are attached to deposits 920 that are covered with a layer of flux 930.

[0080] In summary, a method and device for applying viscous media on a substrate is provided, wherein flux is provided by a non-contact dispensing process on a deposit of solder paste that is arranged on a substrate onto which electronic components can be mounted.

[0081] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. Additionally, 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. 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 measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.