CA1241237A

CA1241237A - Continuous solder processing system

Info

Publication number: CA1241237A
Application number: CA000481480A
Authority: CA
Inventors: Donald J. Spigarelli; James L. Finney; Douglas J. Peck
Original assignee: HTC Corp
Current assignee: HTC Corp
Priority date: 1984-05-25
Filing date: 1985-05-14
Publication date: 1988-08-30
Also published as: FR2564764A1; DE3518405A1; GB2159084B; SG83390G; GB2159084A; BE902496A; KR850008604A; FR2564764B1; GB8512983D0; JPS60257971A

Abstract

ABSTRACT
A system and method for the continuous production soldering of circuit boards and other products in which the product is heated by an independently controlled vapor phase system, and solder applied by a separately controlled application system operative to direct one or more controlled and defined streams of solder onto the product. A vessel is provided for containing a heated saturated inert vapor into which the product is introduced prior to solder application. One or more nozzles are disposed within the vessel for directing one or more streams of molten solder to the heated product. After solder application, the product is subjected to a solder leveling or Deb ridging operation by passage past one or more nozzles which direct streams of vapor phase condensate onto the product surfaces. Each of the operations is separately controllable and is substantially independent of the control of the other operations of the overall system.

Description

This invention relates to soldering systems and methods and more particularly to a system and method For the vapor-phase heating of a product and separate application of solder to the heated product.
BACKGROUND OF THE INVENTION
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 hying 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 colnponents are 1 inserted, the lead lengths cannot be longer than the depth of the solder wave or else a board cannot be accommodated in the 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 products.
Another type of production solder system is the drag solder system in which a reservoir of solder is provided into which a product is clipped 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.
The Amman et at U. S. Patent No. Rev 30,399 shows a wave Flow soldering apparatus in which the solder wave is provided at the bottom of a vessel containing a heated, saturated vapor. The product is conveyed through the vapor chamber and is heated by immersion in the vapor phase and soldered by passage through the solder wave. Solder is applied in an anaerobic atmosphere provided by the vapor 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 vapor does not alter the critical design considerations of the wave apparatus.

fur 1 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 vapor phase prior to immersion into the molten solder bath.
The Sarnacki et at U. S. Patent No. 3,825,16~ 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.

I

_ _ _ 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 vapor 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 provided for containing a heated saturated inert vapor into which the product is introduced prior to solder application and by which the product is heated to soldering temperature. 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 on the board.
After solder application, the product is subject to a solder leveling or debriclging operation by passage past one or more nozzles which are operative to direct streams of the vapor phase condensate onto one or more of the product surfaces to drive off any excess solder and level the applied solder to a uniform deposited layer, to remove icicles of solder, or remove solder bridges between adjacent conductive areas of a board or clear solder in the through-holes.
The solder leveling or Deb ridging operation is also accomplished within the heated vapor phase of the vessel.
Each of the operations is separately controllable and is substantially independent of the control of the other operations.
Heating of the product is provided substantially by the heated vapor phase atmosphere within the vessel, and the establishment and control of this vapor atmosphere is separately provided by the vapor 1 phase apparatus. Solder application is provided by the applicator nozzles which, with the associated solder source and pump, independently provide the intended solder streams for the particular product. Solder leveling or Deb ridging is separately accomplished by the solder leveling nozzles which provide the intended vapor phase condensate streams for solder leveling or selected removal.
The system can also provide reflow soldering by means of heat supplied by the vapor phase atmosphere.
The product can be introduced and removed from the processing vessel in any manner suitable for the particular application.
Typically, for a continuous production process, the product is carried on a conveyor into the processing vessel for heating, solder application and solder leveling and/or Deb ridging, and then carried by conveyor out of the vessel.

~LZ~L;Z 37 - pa-According to abroad aspect of the present invention, there is provided a vapor processing system comprising a vessel for containing a processing vapor. Means is provided for heating an electronic liquid contained within the vessel to establish a saturated vapor zone. An inlet throat communicates it and sloped downwardly towards the vessel. An opposing exit throat communicates with and sloped downwardly towards the vessel. A pair of conveying chains extend through the inlet throat vessel and exit throat. Frame means is provided for retaining printed circuit boards for transport through the system. Means is provided for coupling the forward end of the frame means to the conveying chains. Spaced parallel guide means extend across the vessel from the inlet to the exit throat for supporting the opposed rearward corners of the frame means. The guide means each include a first linear portion substantially coliffe-ar with the bottom surface of the exit throat and a second accurate portion for merging the bottom surface of the inlet throat with the first linear portion. The first linear portion comprises means for engaging the forward end of the frame means when the frame is parallel to the inlet throat, whereby following such engagement, the forward end will be displaced upwardly and the rearward end will follow the second arcuate portion until the frame means becomes parallel to the first linear portion.

' I

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a diagrammatic elevation view of a solder system employing a pair of solder application nozzles, and a pair of solder leveling nozzles all within a vapor phase containing vessel;
Fig. 2 is a diagrammatic elevation view of an alternative embodiment of the system of Fig. 1 having single nozzles disposed below the product Fig. 3 is a diagrammatic elevation view of a further alternative embodiment of the system of Fig. 1 having single nozzles disposed above the product;
Fig. 4 is a diagrammatic elevation view of the system in a preferred implementatiorl;
Fig. 5 is a partially cutaway top view of the system of Fig. I
and Fig. 6 is a partially cutaway pictorial view of a solder nozzle assembly.

I

1 DETAILED D Screecher OF THE YE ERRED EMBODIMENTS
A soldering system in accordance with the invention is shown in a preferred embodiment in Fig. 1, this embodiment being especially suited to the soldering of electronic circuit boards. A closed vessel 10 defines an interior vapor phase chamber in which a zone of inert saturated vapor is provided at a predetermined elevated temperature for heating ox a product to be soldered. Heaters 12 are disposed at the bottom of vessel 10 and are operative to heat a vapor phase liquid 14 to a temperature sufficient to provide a saturated vapor 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 vapor zone within the chamber. Products such as circuit boards 27 are conveyed into the 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 vessel lo and exit throat 20, and is operative to convey or transport the circuit boards into and out of the vapor phase chamber. The conveyor 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 solder nozzles 24 and 26 is disposed in the chamber, each in a position to apply a stream of solder onto respective opposite surfaces of the circuit boards which are conveyed past the solder nozzles along the product travel path within the chamber.
A solder pump 28 is disposed within the vessel 10 in a sup 30 containing molten solder to provide solder to nozzles 24 and 26.
The sup 30 collects excess solder which falls or drains from the boards after solder application by the nozzles. The sup also 1 serves as a solder supply or source for the pump 28. A separate solder source may alternatively be provided. The solder pump can alternatively be disposed external to the vessel. A pair of nozzles 32 and 34 is disposed downstream from the solder application nozzles 24 and 26 and is operative to direct vapor phase liquid streams onto the respective surfaces of the circuit boards for purposes of solder leveling and/or Deb ridging; that is, for removing excess solder from the boards and providing a uniform solder layer.
For convenience, these nozzles 32 and 34 are referred to as solder removal nozzles, it being understood that they are operative to provide leveling, Deb ridging or excess solder removal as required.
The vapor phase liquid is supplied to the nozzles 32 and 34 by a pump 36, located external to the vessel 10, the pump drawing the condensate supply from a sup 38 which receives condensed vapor phase liquid from a gutter 40 below the coils 16 and pipe 41.
Heaters 39 are provided in the sup 38 to maintain the liquid therein at the intended temperature. Alternatively the pump 36 can draw condensate From the supply at the bottom of vessel 10, or from a separate source. The pump 36 can also be internal to the vessel.
An overflow pipe 43 drains excess condensate to the vessel 10.
The entrance and exit throats are preferably configured in conjunction with the vessel to minimize the outward flow of vapor from the vessel to the atmosphere. Such configuration can be as shown in U. S. Patent 4,389,797 of the same assignee as this invention. 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 the particular product configurations and specific operational requirements.

~2~%37 g It is preferable for continuous product processing to provide a straight-through or substantially straight-through system in which the product can be conveyed continuously through the system for soldering operations. The entrance and exit throats 18 and 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 vapor loss from the throats to the atmosphere.
The solder removal techniques employed in the present invention are' the subject of US. Patent 4,3-15,042.
The liquid streams of the vapor phase condensate are projected onto the surfaces of the circuit board to remove excess molten solder therefrom and provide a leveling of the applied solder, typically to a thickness of 0.0003 -0.0006 inches. The nozzles 32 and 34 are each angularly adjustable and are also adjustable in spacing from the confronting board surface to provide the intended fluid streams. Typically, the fluid streams are projected onto the product surfaces at angles inclined to the surface of about 15 - 40 and at a pressure of approximately 5 - 40 pounds per square inch. The two nozzles 32 and 34 can be at different orientations with respect to the circuit board. The positioning of the nozzles and the fluid flow conditions therefrom are determined to provide effective solder removal, including the clearance of unwanted solder from holes through the circuit board. Hole clearance can often be more readily accomplished when one of the two nozzles project a stream at or near normal to the board while the other nozzle _ Jo I . ' .

1 projects a stream at an angle opposite to the removal direction of the board.
The soldering system employs three operations, heating of a product entering the vessel chamber, the application of solder to the heated product, and the leveling or selected removal of applied solder, after which the product exits the chamber. Each of these operations is separately controllable and is substantially independent of the control of the other operations of the overall system. The product entering the chamber is heated by the vapor phase atmosphere within the chamber. The establishment and control of the heated vapor atmosphere is provided by the vapor phase apparatus which includes the heaters 12 and vapor phase liquid 14 and the associated heater control. The solder application is provided by the applicator nozzles, and associated solder supply and pump, 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 vapor phase apparatus of the system. Solder leveling is accomplished by the solder leveling nozzles which are of construction and adjustment to separately provide the intended leveling or removal function.
If only one side of the circuit boards 27 is to be processed, the system can be implemented with only bottom nozzles 26 and 34, as shown in Fig. 2, or with top nozzles 24 and 32 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 42 and 45 are coupled to frames 44, which are operative to retain printed circuit boards for transport through vessel 10. The frames 44 are each coupled at their forward end to the driving chains by a coupling 4~9 and include side members or skids 48 which slide along guide surfaces 50 within the vessel 10 and normally within the entrance and exit $ I Lo p 1 throats. The guide surfaces 50 within the vessel follow a downward path at the entrance portion of the vessel, shown by reference 52, and then follows a linear upward path through the vessel which is substantially colinear with the exit throat 20. An idler wheel 54 is provided within the vessel for each chain 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 follows the path of the guide surfaces and assumes an upwardly inclined orientation as shown in Fig. 4 for linear upward travel through the processing chamber. The circuit board, by this means, is conveyed into 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 74 is disposed above the conveyor to resiliently urge the side skids 48 of the conveyor Frame into engagement with grid surfaces 50 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 and 26 are provided on respective sides of the board transported there between 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 o-F 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, I

1 and are adjustable in offset in the range of 1/4 - 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 60 having an elongated linear orifice 62 along the length thereof and a length to provide a solder stream to the entire board width. A lip member 64 is adjustable with respect to a lip member 66 to provide an adjustable orifice gap. The orifice has a gap typically in the range of 10 - 30 miss. The cylindrical member is rotatable about a pivot axis to provide for angular adjustment of the orifice to select the intended angle of incidence of the solder stream applied to the confronting board surface. A linkage 68 is coupled to the cylindrical member 60 For upward and downward adjustment of the cylindrical member to select the intended 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 supplied to the nozzles via piping 70 which is coupled to a supply manifold 72 which in turn is coupled to the molten solder source or sup within the vessel 10.
Each of the solder nozzles 24 and 26 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 solder 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 orientation of each nozzle and the distance between the nozzle and board surface is determined to provide the intended quantity o, solder and definition of the solder stream for the particular product being processed. The solder streams are 1 separately controlled to provide the intended application of solder to the circuit board. The product has been heated by the vapor phase within the vessel and is thus at soldering temperature upon introduction to the solder application nozzles.
The solder removal nozzles 32 and I are also adjustable in angular orientation and offset in similar manner to the solder nozzles to provide the desired incident streams of leveling liquid onto the board surface.
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 the board surfaces but without any components thereon, and which may 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 illustrated 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 application by a solder 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 applied to the board prior to its entrance into the solder system, is heated to cause the solder paste to reflow and form a bond between the associated component and conductive areas of the board surface.

1 Reflow soldering is accomplished in known manner by the present system by introduction of the circuit board into the heated saturated vapor within the vessel. The opposite board surface can be soldered by the solder stream from the associated nozzle. The present system is therefore very versatile in providing both solder stream and reflow solder capability within a single apparatus, all within the environment of the heated vapor phase.
The vapor phase atmosphere within vessel 10 is heated to a temperature typically in the range of 415 - 450F. (213 - 232C.).
The solder source is maintained typically in the same range. The solder within sup 30 is maintained in molten state by the heated environment within the vessel. Alternatively, separate heaters can be provided in or around the sup to maintain the solder at the intended temperature. The vapor phase atmosphere is therefore at a temperature 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 solder nozzle is determined in relation to the viscosity of the molten solder, the pressure provided by the pump 28 and the orifice dimensions of the nozzle to produce the intended stream configuration for the 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 vapor 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 meters per minute).
The invention is not to be limited by what has been particularly shown and described except as indicated in the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A vapor processing system comprising a vessel for containing a processing vapor, means for heating an electronic liquid contained within said vessel to establish a saturated vapor zone, an inlet throat communicating with and sloped downwardly towards said vessel, an opposing exit throat communicating with and sloped downwardly towards said vessel, a pair of conveying chains extending through said inlet throat, vessel and exit throat, frame means for retaining printed circuit boards for transport through the system, means for coupling the forward end of said frame means to said conveying chains, spaced, parallel guide means extending across said vessel from the inlet to the exit throat for supporting the opposed rearward corners of said frame means, said guide means each including a first linear portion substantially colinear with the bottom surface of said exist throat and a second arcuate portion for merging the bottom surface of said inlet throat with said first linear portion, said first linear portion comprising means for engaging the forward end of said frame means when said frame is parallel to said inlet throat, whereby following such engagement said forward end will be displaced upwardly and said rearward end will follow said second arcuate portion until said frame means becomes parallel to said first linear portion.

2. A vapor processing system according to claim 1, wherein said coupling means includes pin means secured to said conveying chains.

3. A vapor processing system according to claim 1, wherein said second arcuate guide means portion is short in length when compared to the length of said first linear portion.

4. A vapor processing system according to claim 1, wherein said frame means includes side skid members and further comprising a pair of hold down plates disposed above said conveying chains for resiliently engaging said frame means to hold said side skid means against said linear portion of said guide means.