GB2159083A

GB2159083A - Vapour phase soldering

Info

Publication number: GB2159083A
Application number: GB08512982A
Authority: GB
Inventors: Donald Joseph Spigarelli; Douglas John Peck; James Lee Finney
Original assignee: HTC Corp
Current assignee: HTC Corp
Priority date: 1984-05-25
Filing date: 1985-05-22
Publication date: 1985-11-27
Also published as: CA1241236A; FR2564763A1; SG49291G; BE902497A; KR850008603A; DE3518444A1; GB2159083B; JPS60257970A; GB8512982D0

Abstract

In the continuous production soldering of circuit boards (27) and other products the product (27) is heated by an independently controlled vapour phase system, and solder is applied by a separately controlled application system operative to direct one or more controlled and defined streams of solder onto the product (27). A vessel (10) is provided for containing a heated saturated inert vapour into which the product (27) is introduced prior to solder application. One or more nozzles (24,26) are disposed within the vessel (10) for directing one or more streams of molten solder to the heated product (27). The heating and soldering operations are separately controllable and are each substantially independent of the control of the other. A combination of solder steam application and reflow soldering may be carried out. The products lie in frames moved by chains. <IMAGE>

Description

SPECIFICATION Soldering system and method This invention relates to soldering systems and methods and more particularly to a system and method for the vapour-phase heating of a product and separate application of solder to the heated product.

Soldering is widely employed for the fabrication of many different products, especially products in the electronics field, notably printed circuit boards.

For the production fabrication of printed circuit boards and similar products, wave solder systems have been widely employed. These systems include a reservoir of molten solder which is pumped in a wave, with the circuit board being transported in contact with the wave to cause wetting of the intended areas of the board. The solder wave serves as a source of heat for heating of the circuit board and also as the solder source for application of solder to the board. The wave solder apparatus is relatively complex and must be carefully designed and constructed to provide a solder wave of the appropriate dimensions and characteristics to provide the requisite heating and solder application to the particular product being processed. The length of the wave must be sufficient to provide sufficient time of contact to heat the surface to be soldered.The wave design is critical in relation to the product and speed of the product through the wave. There is a maximum speed beyond which a product cannot be conveyed through a particular solder wave and still achieve sufficient heating. For greater speeds, the wave would have to be reconfigured, which would necessitate a complete system redesign.

The height of the solder wave is also a critical factor and can be a limiting factor to the size of a product being processed. For example, in a printed circuit board in which leaded components are inserted, the lead lengths cannot be longer than the depth of the solder or else a board cannot be accommodated in a particular wave solder apparatus because of interference with the long component leads. Thus, care must be exercised in the assembly of components on a circuit board to assure that the lead lengths are less than the depth of the solder wave for the particular solder apparatus to be employed. Since the solder wave serves both as the source of solder and source of heating, the dynamics of the system become complex in designing a wave solder apparatus for particular purposes.Also, these dynamics make it difficult to alter the characteristics of the solder wave to accommodate different types of product.

Another type of production solder system is the drag solder system in which a reservoir of solder is provided into which a product is dipped and immersed either partially or completely to apply solder to the product. Here again the molten solder serves both as the source of heat for heating the product to a soldering temperature and as the solder applicator.

U.S. Reissue Patent No. Re. 30,399 show a wave flow soldering apparatus in which the solder wave is provided at the bottom of a vessel containing a heated, saturated vapour. The product is conveyed through the vapour chamber and is heated by immersion in the vapour phase and soldered by passage through the solder wave. Solder is applied in an anaerobic atmosphere provided by the vapour phase but there is little improvement in the control or performance of the soldering operation by location of the solder wave apparatus in the chamber.

The criticality and relative complexity of the solder wave remains the same as described above, and the presence of the solder wave within the heated vapour does not alter the critical design considerations of the wave apparatus.

An article entitled "A New Soldering Process," by W. R. George, Brazing & Soldering. No. 5 Autumn 1983, shows a drag soldering system in which the product is initially placed within a heated inert vapour phase prior to immersion into the molten solder bath.

U. S. Patent No. 3,825,164 shows a soldering system having a tank containing a pool of molten solder at the bottom and covered by a liquid fluxing bath, with solder spray apparatus within the fluxing bath. A printed circuit card is inserted vertically into the fluxing bath for fluxing and preheating, and solder is sprayed onto one or both surfaces of the printed circuit card as the card is withdrawn from the tank.

The present invention provides a system for the soldering of circuit boards and other products in which the product is heated by an independently controlled vapour phase system, and solder applied by a separately controlled nozzle applicator system operative to direct controlled and defined streams of solder onto the product. A vessel is is provided for containing a heated saturated inert vapour into which the product is introduced prior to solder application and by which the product is heated to soldering temperture. One or more nozzles are provided within the vessel for directing one or more streams of molten solder to the heated product, the impinging solder being retained by the areas of the product surfaces to which the solder will adhere.In the case of a circuit board, the solder is adherent to the conductive circuit paths, the plated-through holes which may be present in the circuit board, and to the leads or connection pads of components assembled on or inserted through the board.

Heating of the product is provided substantially by the heated vapour phase atmosphere within the vessel, and the establishment and control of this vapour atmosphere is separately provided by the vapour phase apparatus. Solder application is provided by the applicator nozzles which, with the associated solder pump and solder source, independently provide the intended solder streams for the particular product. Thus, the heating of the product and solder application to the product are separately controlled operations, and these operations are substantially independent of each other.

The product can be introduced and removed from the processing vessel in any manner suitable for the particular application. Typically, for a continuous production proces, the product is carried on a conveyor into the processing vessel for heating and solder application, and then carried by conveyor out of the vessel.

There now follows a detailed description, to be read with reference to the accompanying drawings, of a soldering system embodying the invention. It will be realised that this system has been selected for description to illustrate the invention by way of example and that the invention may reside in any novel feature or combination of features described.

In the accompanying drawings: Figure 1 is a diagrammatic elevation view of a soldering system embodying the invention; Figure 2 is a diagrammatic elevation view of a second system embodying the invention generally similar to that shown in Figure 1 but having a single nozzle disposed below the product; Figure 3 is a diagrammatic elevation view of a third embodiment of the invention showing a system generally similar to that of Figure 1 but having a single nozzle disposed above the product; Figure 4 is a diagrammatic elevation view of a preferred system embodying the invention; Figure 5 is a partially cutaway top view of the system of Figure 4; and Figure 6 is a partially cutaway pictorial view of a solder nozzle assembly.

A soldering system embodying the invention is shown in Figure 1, this preferred embodiment being especially susited to the soldering of electronic circuit boards. A closed vesel 10 defines an interior vapour phase chamber in which a zone of inert saturated vapour is provided at a predetermined elevated temperature for heating of product to be soldered. Heaters 12 are disposed at the bottom of vessel 10 and are operative to heat a vapour phase liquid 14, typically Fluorinert FC-70, to a temperature sufficient to provide a heated saturated vapour of that liquid within the chamber.

Cooling coils 16 can be disposed around the vessel walls at a position to define the upper extent of the vapour zone within the chamber. Products such as circuit boards 27 are conveyed into the vapour phase chamber by means of an entrance throat 18, and out of the chamber by means of an exit throat 20, each throat outwardly extending from opposite side walls of the vessel 10. A conveyor 22 extends through the entrance throat 18, interior chamber of the vessel 10 and the exit throat 20, and is operative to convey or transport the circuit boards into and out of the vapour phase chamber. The conveyor 22 can be of any suitable form to accommodate the particular product being processed. For circuit boards, the conveyor can include frames for holding the board edges, leaving the board surfaces exposed for soldering.A pair of nozzles 24, 26 is disposed in the vapour phase chamber, each in a position to apply a stream of solder onto respective opposite surfaces of the circuit boards which are conveyed past the nozzles along the product travel path within the chamber.

A solder pump 28 is disposed within the vessel 10 in a sump 30 containing molten solder to provide solder to nozzles 24, 26. The sump 30 collects excess solder which falls or drains from the boards after solder application by the nozzles. The sump also serves as a solder supply or source for the pump 28 and the nozzles. A separate solder source may alternatively be provided. The solder sump can alternatively be disposed external to the vessel.

The entrance and exit throats are preferably configured in conjunction with the vessel to minimize the outward flow of vapour from the vessel to the atmosphere. Such configuration can be as shown in U.S. Patent 4,389,797. The present invention is not limited to use with such entrance and exit throats, as many different forms of product ingress and egress to and from the vessel can be provided to suit particular product configurations and specific opertional requirements. It is preferable for continuous processing to provide a straightthrough or substantially straight-through system in which the product can be conveyed continuously throught the system for soldering operations.The entrance and exit throats 18, 20 can be disposed in a substantially horizontal position or can be inclined upward or downward to provide an intended conveyance path and the requisite minimization of vapour loss from the throats to the atmosphere.

The heating of a product entering the vessel chamber, and the application of solder to the heated product, are separately controllable and are each substantially independent of the control of the other. The product entering the chamber is heated by the vapour phase atmosphere within the chamber. The establish- ment and control of the heated vapour atmosphere is provided by the vapour phase apparatus which includes the heaters 12 and vapour phase liquid 14 and the associated heater control. The solder application is provided by the applicator nozzles 24, 26, and associated source e.g. sump 30 and pump 28, which are constructed and adjusted to provide the intended solder streams for the product which has, prior to solder application, been heated to an intended temperature by the vapour phase apparatus of the system.

If only one side of the circuit boards 27 is to be processed, the system can be implemented with only a bottom nozzle 26, as shown in Figure 2, or with a top nozzle 24, as shown in Fig. 3.

The system of Fig. 1 is shown in typical implementation in Figs. 4 and 5. A pair of conveyor chains 31 and 32 are coupled to frames 34 spaced along the chains and which are operative to retain printed circuit boards for transport through vessel 10. The frames 34 are each coupled at their forward end by a coupling 35 to the driving chains 31, 32, and include side members or skids 36 which slide along guide surfaces 38 within the vessel 10.

The guide surfaces within the vessel follow a downward path 40 at the entrance portion of the vessel and then follow as uniform upward path through the vessel which is substantially colinear with the exit throat 20. A pair of idler wheels 42, 44 is provided within the vessel for the respective chains 31, 32 to change the direction of chain motion, as illustrated. After entrance of a frame and the circuit board carried thereby into the vessel, the frame and circuit board follow the path of the guide surfaces 38 and assume an upward inclined orientation as shown in Fig. 4 for linear upward travel through the processing chamber.The circuit board, by this means, is conveyed in an intended orientation for uniform travel past the solder nozzles so that an intended relative position between the board surfaces and the confronting nozzles can be maintained within the shortest convenient vessel length in order to minimize the length of time that the circuit board is subject to the high temperatures of the processing zone within the vessel.

A pair of hold-down plates 64 is disposed above the conveyor to resiliently urge the side skids 36 of the conveyor frame into engagement with guide surfaces 38 and hold the frame and circuit board contained by the frame down against the guide surfaces. The circuit board is thus maintained in an accurate guided position and orientation along its path past the solder nozzles.

The solder nozzles 24, 26 are provided on respective sides of the board transported therebetween astride the travel path, and each nozzle is adjustable in the angular orientation of the nozzle orifice with respect to the circuit board, and in the offset or spacing of the nozzle from the confronting board surfaces. Typically, the nozzles are angularly adjustable over a range of 45 degrees to either side of an axis normal to the board surface, and are adjustable in offset from the board surfaces in the range of 114 - 1 inch (0.64 - 2.54 cm). The lower nozzle 26 is further illustrated in Fig. 6 and comprises an elongated generally cylindrical tubular member 50 having an elongated linear orifice 52 along the length thereof and of length sufficient to provide a solder stream across the entire circuit board width.The member 50 has a lip 54 adjustable with respect to a lip 56 to provide an adjustable orifice. Typically, the orifice has a gap in the range of 10 - 30 mils (about - 0.254 - 0.762 mm). The cylindrical member 50 is rotatable about its axis to provide for angular adjustment of the orifice 52 to the intended angle of incidence of the solder stream applied to the confronting board surface. A linkage 58 is coupled to the member 50 for upward and downward adjustment of member 50 to select the spacing between the nozzle and the confronting board surface. The upper nozzle 24 is similarly adjustable in offset from the confronting board surface and angular orientation. Molten solder is pumped to the nozzles via piping 60 which is coupled to a supply manifold 62 which in turn is coupled to the molten solder source or sump.

Each of the nozzles is adjustable to provide a selectable angular orientation of the nozzle with respect to the confronting board surface, and to select the gap or distance between the nozzle and the confronting board surface. The angular adjustability of each nozzle provides an angle of incidence for the impinging solder stream which can be normal to the board surface or at an angle with or against the travel direction of the board. The angular orintation of each nozzle and the distance between the nozzle and board surface is determined to provide the intended quantity of solder and definition of the solder stream for the particular product being processed. The solder streams are separately controlled to provide the intended application of solder.Since the product prior to solder application has been heated by the vapour phase within the vessel to soldering temperature, the solder application nozzles need be controlled only to provide the desired solder application, and not to heat the product.

The system is useful in soldering a variety of circuit board types. The system can be employed for so-called bare boards which are printed circuit boards having circuit patterns on one or both board surfaces without any components thereon, and which can include through-holes interconnecting the circuit patterns. The system can also be employed for circuit boards containing surface mounted components on one or both surfaces thereof, leaded components having leads which extend through the board, or a mixture of leaded and surface mounted components. The apparatus of the illustrative embodiment can be employed with either or both solder nozzles operative for a particular processing run.In some cases, solder need only be applied to one board surface, in which case the other solder nozzle can be deactivated by appropriate valving of the solder supply to that nozzle.

The system can also be employed for solder stream application by a nozzle to one board surface, with reflow soldering provided on the opposite board surface. In some types of circuit boards, it is preferable to attach components on a board surface by reflow solder techniques in which, for example, a solder paste is applied to the board, and the board thereafter is heated to cause the solder paste to reflow and form a bond between the associated component and conductive areas of the board surface. Reflow soldering can be accomplished in known manner by the present system by introduction of the circuit board into the heated saturated vapour within the vessel. The opposite board surface can be soldered by the solder stream from the associated nozzle.The present system is therefore versatile in providing both solder stream and reflow solder capability within a single apparatus, all within the environment of the heated vapour phase.

The vapour phase atmosphere within vessel 10 is heated to a temperature typically in the range of 415 - 450 F. (213 - 232 C. The solder source is maintained typically in the same range. The solder within sump 30 is maintained in molten state by the heated environment within the vessel. Alternatively, separate heaters can be provided in or around the sump to maintain the solder at intended temperature. The vapour phase atmosphere is therefore at a temperture sufficient for heating the circuit boards to soldering temperature so that, prior to solder stream application by the solder nozzles, the product is already at the soldering temperature. The solder stream of each nozzle is determined in relation to the viscosity of the molten solder, the presssure provided by the pump 28 and the orifice dimensions of the nozzle to produce the intended stream configuration for proper impingement of solder upon the board. The product is conveyed through the system at a speed sufficient to provide heating of the board by the vapour phase atmosphere within vessel 10 and proper application of solder to the heated product. In typical implementation, the circuit boards are conveyed through the vessel at a speed of 4 - 10 feet per minute (1.20 - 3.05 metres per minute).

Claims

ClAIMS

1. A continuous soldering system comprising: a vapour phase chamber within a vessel; means for generating a heated saturated inert vapour within said chamber at a temperature for heating a product prior to solder application; means for transporting the product into and out of the vapour phase chamber; at least one nozzle disposed in said vapour phase chamber and confronting the path of the product through the chamber; and a solder source coupled to at least one nozzle, the nozzle being operative to direct a stream of solder against the heated product as the product is transported through the vapour phase chamber.

2. A system for soldering circuit boards comprising: a vessel defining a vapour phase chamber; means for providing a heated saturated inert vapour within the chamber at a temperature for heating the circuit boards to soldering temperature prior to solder application; means for conveying the circuit boards through the vapour phase chamber; a solder source; and at least one solder application nozzle coupled to the solder source and disposed within the vapour phase chamber for directing a stream of molten solder onto the heated circuit boards.

3. A system for the soldering of a product comprising: a vessel defining a vapour phase chamber; means for providing a heated saturated inert vapour in the chamber at a controlled temperture for heating the product prior to solder application; means for conveying the product through the vapour phase chamber; and characterised by a source of molten solder; and one or more nozzles coupled to the solder source and disposed within the vapour phase chamber and operative to direct respective streams of molten solder to the heated product.

4. A system according to claim 3, wherein the solder source is disposed within the vapour phase chamber.

5. A system according to either one of claims 3 and 4, wherein the vessel includes an entrance throat and an exit throat each outwardly extending from opposite side walls of the vessel and through which the product is conveyed into the vapour phase chamber for heating and solder application.

6. A system according to claim 1, wherein said at least one nozzle is adjustable in distance from the confronting surface of the product conveyed through the vapour phase chamber and in the angle of the solder stream projected onto the product surface.

7. A solder system according to any one of claims 3 to 5, wherein said means for providing the vapour includes means for controlling the temperature of the vapour to provide heating of the product to a temperature at least at the soldering temperature of the product prior to solder application.

8. A system according to any one of claims 3 to 5 and 7, comprising means for maintaining the product in a predetermined orientation during its travel past the one or more nozzles.

9. A system according to claim 8, wherein the maintaining means includes guide means disposed in the vessel and means for urging the product into engagement with the guide means during product conveyance through the vessel.

10. A system according to either one of claims 8 and 9, wherein said maintaining means includes guide means disposed in the vessel having a downwardly inclined path at the entrance portion of the vessel a linear upward path through the remaining portion of the vessel; said one or more nozzles being disposed along the linear upward path.

11. A system according to any one of claims 3 to 5 and 7 to 10, wherein the conveying means includes a pair of conveyor chains disposed along a conveyor path through the vessel; and a plurality of frames each linked to the conveyor chains in spaced apart relation to adjacent frames, each of the frames being operative to retain the product therein.

12. A system according to any one of claims 3 to 5 and 7 to 11, wherein each of said one or more nozzles is adjustable in distance from the confronting surface of the product conveyed through the vapour phase chamber and in the angle of the solder stream projected onto the product surface.

13. A system according to any one of claims 3 to 5 and 7 to 11, wherein each of said one or more nozzles is adjustable in distance from the confronting surface of the product conveyed through the vapour phase chamber.

14. A system according to any one of claims 3 to 5 and 7 to 11, wherein each of said one or more nozzles is adjustable in the angle of the solder stream projected onto the product surface.

15. A system for soldering circuit boards comprising: a vessel defining a vapour phase chamber; means for providing a heated saturated inert vapour within the chamber at a temperature for heating the circuit boards to soldering temperature prior to solder application; an entrance throat and an exit throat each outwardly extending from opposite side walls of the vessel; means for conveying circuit boards through the entrance throat, vapour phase chamber of vessel and exit throat; a source of molten solder; and one or more nozzles coupled to the solder source and disposed within the vapour phase chamber and operative to direct respective streams of molten solder to the heated circuit boards; the construction and arrangement being such that the entrance and exit throats provide a substantially straight-through conveyance path through the vessel and entrance and exit throats for heating of the circuit boards and solder application within the vapour phase chamber.

16. A system according to claim 15 wherein the vapour providing means includes heaters at the bottom of the vessel operative to heat a vapour phase liquid to provide said saturated inert vapour within the vapour phase chamber.

17. A system according to claim 16, wherein said vessel includes cooling coils around the vessel walls at a position to define the upper extent of the vapour within the vapour phase chamber.

18. A system according to any one of claims 15 to 17 wherein each of the nozzles includes: an elongated tubular member having an elongated linear orifice of a length sufficient to provide a solder stream across the entire width of the circuit board; and piping means coupling said tubular member to the solder source for supplying molten solder to the tubular member and orifice.

19. A system according to claim 18 wherein each elongated linear orifice is adjustable in a direction normal to its length to provide further control of the solder stream.

20. A system for the soldering of a product comprising: a vessel defining a vapour phase chamber; means for providing a zone of saturated inert vapour within the chamber at a selected elevated temperature to heat the product to a predetermined temperature prior to solder application; means for conveying the product into and out of the vapour zone along a travel path; a source of molten solder; and one or more nozzles coupled to the solder source and disposed within the vapour zone and each operative to direct a stream of molten solder to the heated product to apply solder to the product.

21. A system according to claim 20 wherein at least one pair of the nozzles are disposed astride the product travel path to direct the streams of molten solder onto opposite surfaces of the heated product.

22. A system according to either one of claims 20 and 21 wherein the heating of the product prior to solder application and the application of the solder are separately controllable and are each substantially independent of the control of the other.

23. A system according to any one of claims 20 to 22 wherein each nozzle is separately controllabe to provide the desired application of the solder.

24. A system according to any one of claims 20 to 23 comprising means to return excess solder not adhering to the prodeuct to the solder source.

25. A system according to any one of claims 20 to 24 wherein the solder source is disposed within the vapour zone.

26. A system according to any one of claims 20 to 25 wherein the travel path of the product is a continuous, substantially straight-through path.

27. A method for soldering of a product comprising: establishing a zone of saturated inert vapour at a selected elevated temperature; conveying the product along a travel path into and out of the vapour zone; heating the product to a predetermined temperature by exposing it to the vapour in the vapour zone; and subsequently to heating the product to the predetermined temperature and prior to conveying the product our of the vapour zone, applying solder to the product by directing one or more streams of molten solder to the heated product.

28. A method according to claim 27 wherein the travel path is a continuous, substantially straight-through path.

29. A method according to either one of claims 27 and 28 wherein the predetermined temperature to which the product is heated is at or above the reflow temperature of solder applied to the product prior to conveying the product into the vapour zone and further comprising the step of reflowing the preapplied solder by exposing it to the vapour in the vapour zone.

30. A method according to any one of claims 27 to 29 comprising the step of separately controlling each solder stream to provide the desired application of the solder.

31. A system for soldering a product substantially as hereinbefore described with reference to the accompanying drawings.

32. A method of soldering a product substantially as hereinbefore described with reference to the accompanying drawings.