WO1999021676A1

WO1999021676A1 - Soldering method and apparatus

Info

Publication number: WO1999021676A1
Application number: PCT/GB1998/003095
Authority: WO
Inventors: Ralph Miles
Original assignee: Alphr Technology Limited
Priority date: 1997-10-23
Filing date: 1998-10-16
Publication date: 1999-05-06
Also published as: AU9547998A; GB9722305D0

Abstract

A soldering method and apparatus comprise providing a substrate (2), dosing soldering paste (4) onto the substrate (2) at terminals at the upper surface of the substrate (2) and provided by pins (6) of electrical components below the substrate and then passing the substrate (2) to a reflowing station that uses hot gas from specific nozzles (14) to reflow the solder.

Description

SOLDERING METHOD AND APPARATUS

This invention relates to a soldering method and soldering apparatus.

Conventionally reflowing of solder to connect pins of larger electrical components to a printed circuit board would be carried out by hand using a soldering iron, with the attendant low accuracy and possibility for error that this entails.

According to a first aspect of the present invention, there is provided a soldering method comprising providing a support through which extend upwardly at least one electrical conductor of an electrical component below the support to form at least one terminal at an upper surface of said support, applying solder paste to said upper surfaces at said terminal (s), applying hot gas to said paste to heat said paste to cause solder to reflow, and causing or allowing the solder to cool.

According to a second aspect of the present invention, there is provided soldering apparatus comprising duct means for supplying gas, heating means for heating the gas, and a plurality of downwardly directed nozzles arranged to emit respective downward jets of the hot gas onto solder means at respective terminals of an electrical component to heat and thus re-flow said solder means, said nozzles being arranged in a pattern corresponding to a pattern of said terminals of said electrical component.

Owing to these aspects of the invention, it is possible, because of the use of hot gas, to perform the soldering more rapidly than with a soldering iron and, because of performing the soldering at the upper surface of the support, to avoid re-flowing solder dripping from the underneath surface of the support. Moreover, when solder paste is used, it is possible to apply the solder more conveniently, reliably and accurately. According to a third aspect of the present invention, there is provided a soldering method comprising applying solder paste to a support, applying hot gas to said paste on said support to heat said paste to cause solder to re-flow, and causing or allowing the solder to cool, characterised by guiding upwardly away from said at least one terminal the hot gas which has heated said paste.

According to a fourth aspect of the present invention, there is provided soldering apparatus comprising duct means for supplying gas, heating means for heating the gas, and at least one nozzle arranged to emit at least one jet of the hot gas onto solder means of at least one terminal of an electrical component to heat and thus re-flow said solder means, characterised by guiding means arranged to guide upwardly away from said at least one terminal the hot gas which has heated said solder means.

According to a fifth aspect of the present invention, there is provided a soldering method comprising applying solder paste to a support, applying hot gas to said paste on said support to heat said paste to cause solder to re-flow, characterised by forming a shield of cold gas bounding said hot gas at said paste.

According to a sixth aspect of the present invention, there is provided soldering apparatus comprising duct means for supplying gas, heating means for heating the gas, and at least one nozzle arranged to emit at least one jet of the hot gas onto solder means of at least one terminal of an electrical component to heat and thus re-flow said solder means, characterized by cooling means arranged to form a shield of cold gas bounding the hot gas at the solder means.

Owing to these aspects of the invention, it is possible to avoid undesired heating of adjacent zones of the support and thus to avoid damage to adjacent soldered joints and/or components and/or the support itself.

According to a seventh aspect of the present invention, there is provided a soldering method comprising applying a dosed blob of solder paste to a terminal of a component on an electrical circuit board, heating said blob to cause solder to reflow at said component, and causing or allowing the solder to cool.

Owing to this aspect of the invention, it is possible to apply solder paste to a component terminal reliably and

SUBSTITUTE SHEET(RULE 2B) accurately .

According to an eight aspect of the invention, there is provided soldering apparatus comprising a hot-gas applying tool, and a nozzle head releasably mounted in said tool, said nozzle head including at least one nozzle arranged to emit at least one jet of the hot gas onto solder means at at least one terminal of an electrical component to heat and thus reflow said solder means.

Owing to this aspect of the invention, it is possible to change nozzle heads to suit particular patterns of terminals of electrical components.

The components to which the invention is applicable are not only through-board components but also surface-mounted devices (S D' s) . In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a perspective view from above illustrating diagrammatically a soldering method, Figure 2 is a side elevation of a hot-air applying tool employed in the method,

Figure 3 is a top plan view of a dosing station of a preferred embodiment of a machine employable in the method,

Figure 4 is a vertical section view taken along the line IV-IV of Figure 3,

Figure 5 is a front elevation of a soldering station of the machine,

Figure 6 is a side elevation of the soldering station,

Figure 7 is an axial section through one of a range of multi-nozzle, hot-air applying heads usable in the soldering station,

Figure 8 is a fragmentary, side elevation of the head of Figure 7,

Figure 9 is an end elevation of the head of Figure 7, and

Figure 10 is a different axial section through the head of Figure 7.

Referring to Figure 1, a printed circuit board 2 has had printed thereon a plurality of sets of caps 4 and has had inserted through corresponding sets of holes through the board corresponding sets of pin-form terminals 6 of through- board electrical components 8. By relative movement between the board 2 and a dispensing syringe 10 (or if desired a corresponding set of dispensing syringes), the pins 6 of a set and their pads 4 are brought one after another to directly beneath the syringe 10 (or brought simultaneously to directly beneath the syringes of the set) and the syringe 10 delivers to the pins 6 and their pads 4 respective metered doses of solder paste (for example "LOCTITE ® Product 3831") to form respective blobs 12 around the pins 6. Then, by relative movement between the board 2 and a hot-air applying tool 14, the blobs 12 become face-to-face with open mouths of a corresponding set of downwardly directed nozzles 16 which apply hot air at a temperature of about 300 'C to the respective blobs 12 of solder paste so causing the solder therein to reflow, the continuous supply of hot air through the nozzles 16 overcoming any heat sink effect of the components 8.

By the method described with reference to Figure 1, it is possible accurately to apply to each terminal a desired amount of solder paste in the desired place and then accurately to apply heat to each blob at a desired temperature for a desired period of time, thereby to reflow the solder in each blob 12 and to heat each pin 6 without causing blistering of the solder or burning of the component 8.

The weight of solder paste in each blob 12 is at least 0.03g., preferably from 0.05g. to 0.15g., particularly advantageously about 0.07g.

Referring to Figure 2, the tool 14 includes a heater casing 18 in which is an electrical heating element supplied through a lead 20 and through which is fed compressed air supplied to an inlet 22. The heated compressed air is fed from the casing 18 to an outlet sleeve 24 to which can be selectively connected any one of a range of nozzle heads (of which one is shown and referenced 26) , the nozzles of each of

SUBS11 lUTE SHEET (RULE 26) which are arranged in a pattern corresponding to a pattern of terminals of an electrical component to which the head is dedicated. Each nozzle head 26 includes, immediately upstream of the nozzles 16, a distribution chamber 28 to promote even distribution of the hot air among the nozzles 16.

The dosing station 40 of Figures 3 and 4 comprises two syringes 41 and 42 that are fixed via respective clamps 57 to respective mounts 43 and 44. The mounts 43 and 44 are each movable laterally by respective endless belts 45 and 46. Each belt is driven from respective belt drive assemblies 47 and 48, with corresponding respective idling wheels 49 and 50 at the opposite ends. Bars 51 and 52 support and guide the respective mounts 43 and 44 and support the respective belt drive assemblies 47 and 48. Each bar 51 and 52 is movable laterally by endless belts 53 and 54 driven by respective drive assemblies 55, with an idling wheel 56 at the opposite end of each belt. Each syringe 41 and 42 is also movable vertically as the clamps 57 can be moved up and down on the respective mounts 43 and 44, as desired, by respective drive assemblies 58. The drive assemblies 47, 48, 55 and 58 are controlled by a microprocessor (not shown) and therefore the position of each of the syringes 41 and 42 can be set with great accuracy to provide solder paste to a substrate 60 as required by the particular application. Once the syringe 41 or 42 is in the correct position it is lowered, and the correct dose of solder paste is expelled from the syringe 41 or 42. The process of dosing can be controlled manually or set to specific instructions executed by the microprocessor. An indexing conveyor 61 can advance the substrate 60 to a position ready to receive the dosed solder paste, hold it in position while receiving the paste, and then pass it to the soldering station 170 for reflowing the solder.

Figures 5 and 6 show the station 170 having received the substrate 60 on the conveyor 61. The station 170 is provided with four tools 62 to 65 that are adapted to provide hot gas and cold gas simultaneously. The hot gas is to reflow the solder paste, while the cold gas is to protect those components, or parts of components, that might suffer damage trom the heat of the hot gas.

Each tool 62 to 65 has a nozzle head (not shown) attached to it that is designed to be of a particular form appropriate to the reflow job for which it is intended. An assembly 66 carries blocks 67 to 70 that supply the respective tools 62 to 65 with the gas.

Each of the blocks 67 to 70 can slide up and down independently of the remainder of the station 170, under the control of respective drive assemblies 71, in holders 72 to 75, all of which are mounted on the assembly 66. The assembly 66 is fixed to a frame 82 that is slidably mounted in an upright bracket 76 that has a cross-piece 77 slidably mounted on two horizontal rods 78 along which the cross-piece 77 is movable. The movement is controlled by a piston-and-cylinder device 79,80. The piston 79 is fixed to the cross-piece 77 via a plate 81. Therefore, the assembly 66 can be moved up and down and back and forth as desired. When the assembly 66 is close to the substrate 60, the nozzles can be individually lowered to provide the hot gas to reflow the solder for a particular length of time desired for each individual electrical component.

Figures 7 to 10 show a nozzle head 90 that could be affixed to any one of the tools 62 to 65. A central chamber 91 of the head 90 supplies the hot gas via nozzles 92 to the blobs of solder paste that are to be reflowed on the substrate 60. The hot gas rebounds from the substrate 60 and is directed upwards and outwards into exhausts 94; the web- form barriers 100 which come very close to the upper surface of the substrate 60 are shaped to facilitate this. This reduces the chance that the hot gas may damage any nearby components susceptible to heat. The cold gas is supplied through an external tube 96 to a nozzle 99 to create a cool zone 97, which is where part of the component is when the hot gas is reflowing the solder paste. The cool gas exits from the ends of the zone 97. The nozzle head 90 is provided with a hole 101 that sits over a protruding component on the substrate 60.

An alternative or addition to the barriers 100 and the exhausts 94 for guiding the hot gas away from the substrate zones around the head 90, is that the head could be provided with ducts whereby the hot gas is drawn away by suction and recycled.

Claims

C AIMS

1. A soldering method comprising providing a support through which extend upwardly at least one electrical conductor of an electrical component below the support to form at least one terminal at an upper surface of said support, applying solder paste to said upper surfaces at said terminal (s) , applying hot gas to said paste to heat said paste to cause solder to reflow, and causing or allowing the solder to cool.

2. A method according to claim 1, wherein said applying of said solder paste to said upper surface comprises applying said solder paste to at least one electrically conductive zone of a printed circuit board and extending adjacent said terminal (s) , and wherein said applying of said hot gas to said paste heats not only said paste but also said terminal (s) and said electrically conductive zone(s).

3. A method according to claim 1 or 2, and further comprising guiding upwardly away from said at least one terminal the hot gas which has heated said paste.

4. A method according to claim 3, wherein said guiding comprises diverting upwardly and outwardly the hot gas which has heated said paste.

5. A method according to claim 3 or 4, wherein said guiding comprises drawing away by suction the hot gas which has heated said paste.

6. A method according to any preceding claim, and further comprising forming a shield of cold gas bounding said hot gas at the paste.

7. A method according to any preceding claim, wherein said applying of said hot gas to said paste includes applying a plurality of jets of said hot gas to respective terminals.

8. A method according to any preceding claim, wherein said paste is applied to said upper surface at the or each terminal in the form of a dosed blob.

9. A method according to claim 8, wherein the or each blob is of a weight greater than 0.03g.

10. A method according to claim 9, wherein the or each blob is of a weight between 0.05g. and 0.15g.

11. A method according to claim 10, wherein the or each blob is of a weight of substantially 0.07g.

12. A method according to any one of claims 2 to 8, wherein the or each electrical conductor comprises a projecting portion of a pin which has been inserted through said support .

13. A soldering method comprising applying solder paste to a support, applying hot gas to said paste on said support to heat said paste to cause solder to re-flow, and causing or allowing the solder to cool, characterised by guiding upwardly away from said at least one terminal the hot gas which has heated said paste.

14. A method according to claim 13, wherein said guiding comprises diverting upwardly and outwardly the hot gas which has heated said paste.

15. A method according to claim 13 or 14, wherein said guiding comprises drawing away by suction the hot gas which has heated said paste.

16. A soldering method comprising applying solder paste to a support, applying hot gas to said paste on said support to heat said paste to cause solder to re-flow, characterised by forming a shield of cold gas bounding said hot gas at said paste.

17. A soldering method comprising applying a dosed blob of solder paste to a terminal of a component on an electrical circuit board, heating said blob to cause solder to reflow at said component, and causing or allowing the solder to cool.

18. A method according to claim 17, wherein the blob is of a weight greater than 0.03g.

19. A method according to claim 18, wherein the blob is of a weight between 0.05g. and 0.15g.

20. A method according to claim 19, wherein the blob is of a weight of substantially 0.07g.

21. Soldering apparatus comprising duct means for supplying gas, heating means for heating the gas, and a plurality of downwardly directed nozzles arranged to emit respective downward jets of the hot gas onto solder means at respective terminals of an electrical component to heat and thus re-flow

SUBSTITUTE SHEET (RULE 25) said solder means, said nozzles being arranged in a pattern corresponding to a pattern of said terminals of said electrical component.

22. Apparatus according to claim 21, wherein said duct means includes a distribution chamber immediately upstream of said nozzles .

23. Apparatus according to claim 21 or 22, wherein said nozzles are contained in a nozzle-head releasably mountable in a hot-gas applying tool.

24. Apparatus according to any one of claims 21 to 23, and further comprising guiding means arranged to guide upwardly away from the terminals the hot gas which has heated said solder means .

25. Apparatus according to claim 24, wherein said guiding means comprises barrier means arranged to divert upwardly and outwardly the hot gas which has heated said solder means.

26. Apparatus according to claim 25, wherein said barrier means are arranged to come to close to said support and said guiding means further comprises upwardly and outwardly directed exhaust port means disposed above said barrier means and into which said barrier means diverts said hot gas which has heated said solder means.

27. Apparatus according to any one of claims 24 to 26, wherein said guiding means comprises suction duct means arranged for drawing away the hot gas which has heated said solder means.

28. Apparatus according to any one of claims 24 to 27 as appended to claim 23, wherein said guiding means is included in said head.

29. Apparatus according to any one of claims 21 to 28, and further comprising cooling means arranged to form a shield of cold gas bounding the hot gas at the solder means.

30. Apparatus according to claim 29 as appended to claim 23, wherein said cooling means is included in said head.

31. Soldering apparatus comprising duct means for supplying gas, heating means for heating the gas, and at least one nozzle arranged to emit at least one jet of the hot gas onto solder means of at least one terminal of an electrical

10

SUBSTITUTE SHEET (RULE 25) component to heat and thus re-flow said solder means, characterised by guiding means arranged to guide upwardly away from said at least one terminal the hot gas which has heated said solder means.

32. Apparatus according to claim 31, wherein said at least one nozzle is included in a nozzle head releasably mounted in a hot-gas applying tool.

33. Apparatus according to claim 31 or 32, wherein said guiding means comprises barrier means arranged to divert upwardly and outwardly the hot gas which has heated said solder means.

34. Apparatus according to claim 33, wherein said barrier means are arranged to come to close to said support and said guiding means further comprises upwardly and outwardly directed exhaust port means disposed above said barrier means and into which said barrier means diverts said hot gas which has heated said solder means.

35. Apparatus according to any one of claims 31 to 34, wherein said guiding means comprises suction duct means arranged for drawing away the hot gas which has heated said solder means.

36. Apparatus according to any one of claims 33 to 35 as appended to claim 32, wherein said guiding means is included in said head.

37. Apparatus according to any one of claims 31 to 36, and further comprising cooling means arranged to form a shield of cold gas bounding the hot gas at the solder means.

38. Apparatus according to claim 37 as appended to claim 32, wherein said cooling means is included in said head.

39. Soldering apparatus comprising duct means for supplying gas, heating means for heating the gas, and at least one nozzle arranged to emit at least one jet of the hot gas onto solder means of at least one terminal of an electrical component to heat and thus re-flow said solder means, characterized by cooling means arranged to form a shield of cold gas bounding the hot gas at the solder means.

40. Apparatus according to claim 39, wherein said cooling means and said at least one nozzle are included in a nozzle

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SUBSTTTUTE SHEET (RULE 26) head releasably mounted in a hot-gas applying tool.

41. Soldering apparatus comprising a hot-gas applying tool, and a nozzle head releasably mounted in said tool, said nozzle head including at least one nozzle arranged to emit at least one jet of the hot gas onto solder means at at least one terminal of an electrical component to heat and thus reflow said solder means.

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SUBSTTTUTE SHEET (RULE 26)