CA1108480A - Wave solder machine - Google Patents

Abstract

D-20,731 WAVE SOLDER MACHINE
by Lee Charles Gumprecht ABSTRACT OF DISCLOSURE

A wave solder machine is provided which includes an endless moving mesh belt that is made of a nonsolderable material such as titanium wire. The belt is supported so as to be totally immersed in the solder wave as it passes the latter.
This causes the undersides of stuffed printed circuit boards on the belt to be brought into contact with the molten solder.
The belt wires preferably have a plurality of projections thereon to support the circuit boards above the major portion of the belt. In another machine, the circuit boards are moved along a plurality of parallel wires that pass through the solder wave. Alternatively, the wires themselves may be moving for carrying circuit boards across the solder wave.

Description

!L1(~84~0 1 ¦WAVE SOLDER ~ACHINE

3 ¦BACKGROUND OF INVENTION
I ~
alThis invention relates to wave solder machines and 51 more particularly to a wave solder machine ~or processing 6¦ stuffed printed circuit (PC) boards of different and random l and shapes 71 sizes/without the use of carriers for holding individual 81 circuit boards.
9¦ A prior art method of producing circuit boards lO¦ carrying electrical circuits is to assemble and process the ll¦ boards on a progressive production line. Circuit boards 12¦ having conductive traces thereon are located between a pair 13¦ of tracks of a conveyor, which hold the boards by the edges 14 thereof. As the tracks move the boards they are stuffed with components, fluxed, soldered, trimmed ~the component leads 16 thereon), and cleaned. In the wave solder machine in such 17 a progressive line, the conveyor tracks hold the PC boards 18 by edges thereof as the conveyor moves the undersides of the 19 boards into contact with the solder waveO Such an assembly technique is only economically feasible when it is desirable 21 to produce a large number of finished circuit boards having 22 the same wldth. --23 In a prlor-art wave solder machine for soldering 24 component leads on circuit boards of size which occur in relatively small numbers, an operator must load the boards 26 into carriers or racks having fixed outer dimensions and 27 adjustable bars which hold the boards by edges thereof. Such 28 a carrier is described in U. S. Patent No. 3,930,644, issued ~0 ' ' - 1 -`~ ~

1¦ January 6, 1976 to E. V. Albert, Jr. The opexator stuffs the 21 racked circuit board with components and then places the 31 carriers on conveyor tracks of fixed dimensions which carry ~¦ the undersides of the stuffed and racked circuit boards into 5I contact with the solder wave. The hand operations of loading 61 circuit boaxds into and unloading them from such carriers 7I involves considerable time and expense. The carriers them-selves are also costly ana re~uire constant maintenance.
9¦ An object. . of this invention is the provision of an 10¦ improved wave solder machine that is particularly adapted ll¦ for economically and efficiently processing circuit boards 12¦ of different sizes and shapes as well as large production runs 13 of circuit boards of the same size.

SUMMARY O~ INVENTION
16 In accordance with this invention, a wave solder 17 machine comprises means for producing a wave of molten solder;
18 an elongated mesh belt for supporting stuffed printed circuit }9 boards in the machine by the undersides thereof, said belt being immersed in and extending through the solder wave in a.prescribed 21 direction; and means for moving the belt in the prescribed di-22 rec-tion with portions of the undersides of circuit boards con-23 tacting said belt for causing the undersides of the boards to

2~ contact the molten solder wave as said belt moves through the solder wave and the boards move past it. A method in accordance ~0 32 f/- 2 :1¦ with this invention for soldering leads of components stuffed -2¦ in printed circuit boards to conductive patterns on the under-31 side of the boards compxises the steps of: producing a wave of 41 molten solder having a width that is greater than a broad 51 dimension of a stuffed circuit board to be soldered; support-6¦ ing the stuffed circuit board on an elongated mesh belt with 71 portions of the underside of the board contacting portions 81 of the belt which is immersed in and extends through the solder 9¦ wave in a prescribed direction; and moving the belt in the : 10¦ prescribed direction so as to progressively pass all o the 11¦ underside of the board into con-tact with the molten so.lder wave s the lt passes ~hrough it e~J ~

1l DESCRIPTION OF DRA~INGS
I . . ... .
2¦ This invention will be more fully understood from 31 the following detailed description together with the attached 41 drawings in which:
51 FIG. 1 is a side elevation view of a wa~e solder ¦ machine 10 embodying this invention, with the side plate 40 7 ¦ broken away to show the solder wave 26;
8 ¦ FIG. 2 is an enlarged perspective view of the top 9¦ of a portion of the machine in FIG. 1 with the belt 12 10¦ partially cut away over the solder station 22;
11¦ FIG. 3 is a top view of the solder station 22 in 12¦ FIGS. 1 and 2;
13¦ FIG. 4 is a sectîon view of the solder station 22 14¦ taken along line 4--4 in FIGS. 2 and 3i FIG. 5 is an enlarged top view of a portion of the 16 belt 12;
17 FIG. 6 is an enlarged section view of the belt 12 18 taken along line 6--6 in FIG. 5 and in a d.irection opposite 19 to the arrow 15 in FIGS. 2 and 5;
FIG. 7 is an enlarged perspective view of the belt 21 on a drive roller 60;
22 FIG. 8 is a perspective view of a portion of a wave 23 solder machine embodying an alternate form of this invention;
2~ FIG. 9 is an elevation view of the machine in FIG. 8 illustrating the drive and support mechanism for the wires 81 26 thereof;
27 FIG. 10 is an elevation view of a portion of a 28 machine including anotheF embodiment of this invention; and ~0 _ 3 _ ~L~

1 FIG. 11 is an elevation view, taken in the direction 2 of arrow 15, of a machine including yet another embodiment of

3 this invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
6 The wave solder machine 10 in FIG. 1 generally 7 comprises an endless belt 12 which carries stuffed printed 8 circuit boards 14 of different sizes and shapes in the direction 9 of the arrow 15. The belt moves the boards 14 over a wave flux station 16, preheater stations 18 and 20, and a wave 11 solder station ~2 which produces a wave 26 of molten solder.
12 The station 16 is conventional and may be any type of equip-13 ment for applying the flux to the bottom of a PC board 14 on 14 the belt 12.
The wave solder station 22 is shown in more detail 16 in FIGS. 3 and 4. It g~nerally;comprises a pot 28 that i9 17 filled with molten solder 30 to a level below the top edge 32 18 thereof, and which has a container 34 supported therein. In 19 operation~ a pump 36 forces mol~en solder through apex-tures in a top plate 38 on the container to form the wave 26 which 21 may be two inches wide and have a leading edge 26 . The ~2 bread-th of the wave 26 is defined by the end plates 40 and 23 42 on the container 34. The wave may extend as much as an 2a lnch above plate 38. The station 22 is conventional except for the skids 46 and 48 which extend through the solder wave 26 26,and for the fact ~hat belt 12 passes through the wave (see 2~ FIGS. 1 and 2). The skids 4~ and 48 may be lengths of solid 2~ rod having key ways formed in the centers thereof, and 29 ~itting over the top 38 on the container 34. Alternatively, they ~0 may be supported in the solder wave by rigid metal bars that are 31 attached to pot 28 and have right angle flanges on the ends 32 thereof that are attached to the bottoms of the skids.The skidsare , ~ I
I

1 ¦ oriented parallel to each other, spaced a prescribed distance 2 ¦ d from associated end plates ~0 a~d 42, and are secured to 3 ¦ the container top 38 such as by screws (not shown~

4 ¦ As is described more ~ully hereinafter, the belt 12

5 ¦ is preferably a wire mesh screen (see FIG. 2) that is made of I commercially

6 I a nonsolderable material such as/pure titanium or a titanium

7 ~ alloy. Alternatively, the belt may be made of music wire.

8 ¦ This makes it possible ~or the belt to be fluxed and then

9 ¦ completely immersedin and passed d}rectly through the solder

10 ¦ wa~e 26 (as is illustrated in FIGS. 1 and 2) without solder

11 ¦ adhering to it. The belt is pre~erably several inches wider

12 ¦ than the widest printed circuit board to be processed by the

13 ¦ machine 10.

14 ¦ Briefly, an operator normally loads stuffed printed 1~ ¦ circuit boards 14, one a~ter the other, onto the left end 52 16 ¦ of the belt 12 by hand. Alternatively, stuffed circuit boards 17 ¦ 14 may be loaded automatically onto the belt 12 from an adjacent 18 ¦ belt (not shown). As the boards 14 move from left-to-~ight in 19 ¦ FIG. 1, the st~tion 16 applies solder flux on the undersides 20 ¦ thereof to cause the solder to adhere to conductive circuit 21 ¦ traces thereon. Since the belt 12 is made of a nonsolderable 22 ¦ material, however, the solder will not adhere ~o the ~luxed 23 ¦ belt. The belt 12 and circuit boards 14 thereon are gradually Co~ Qr~ \al 2~ ¦ heated in the c4~e~ manner to higher temperatures by 25 ¦ stations 18 and 20 so that they are more nearly the same 26 ¦ temperature as the molten solder when the boards contact the 27 ¦ wave 26. This reduces thermal shock in the boards as they Z8 ¦ come into contact with the solder wave 26. As the belt 12 29 l 31 ~ - 5 -1 passes through the solder wave (see FIG. 2), t~e underside 2 of a circuit board 14 is gradually brought into contact with the solder over the full breadth of the board until the full 4 area of the underside of the board has been brought into contact with the solder wave. Soldered circuit boards 14B
6 on the right side of the belt in FIG. 1 pass over the roller 7 60 and onto another belt ~not shown) which carries them to a cleaning operation.
9 The structure of belt 12 is preferably similar to that of the flat flex belt manufactured by the Wire Belt Company 11 of America, Winchester, Massachusekts. The flat flex belt is 12 described in their catalog No. 72. The belt 12 her~, however, 13 is preferably made of a nonsolderable material.
14 The preferred embodiment of belt 12 is shown in more detail in FIGS. 2, 5, 6 and 7. The belt is comprised 16 of a plurality of single lengths of wires which extend between 17 the edges of the belt (see FIG. 2), portions of only a ~ew 1~ such wires being shown in FIG. 5. The transverse --19 portions o these wires designated by the letter A are parallel to each other and orthogonal to the arrow 15. Conversely, 21 the short portions of these wires designated by the letter 22 B are parallel to each other and arrow 15. Adjacent wires 23 are securely threaded together,as is shown in FIG. 5, to form 24 a flexible belt. A projection 47 which is preferably in the shape of an inverted V is formed in the transverse wire portion 26 55A. Other projections are periodically formed in other 27 transverse wire portions as is shown in FIG. 2. These pro-28 jections provide structure which contacts only a very small ~0 ' ~138':~Y~ ¦

l ¦ portion of the underside of a circuit board 14 and holds it 2 ¦ above the major portion of the belt. As was stated previously, 3 ¦ the belt 12 is preferably made of a nonsolderable material such ¦ as titanium. SimilarIy shaped belts which are made of solderable ¦ materials such as stainless steel have been used in other types 6 ¦ of operation such as defluxin~ operations a~ter wave solder, ¦ and have been used in reflow solder operations where the belts 8 ¦ merely pass through ovens for reflowing the plated material on ¦ the traces of circuit boards having only conductive traces O ¦ thereon and prior to ~oldering of components thereto. The belt ll ¦ does not come into contact with molten solder in such an ~2 ¦ operation. By way of example, the wires of belt 12 are made 13 ¦ of 0.050 inch diameter titanium wire with a mesh size of 0.375 ;~ 14 ¦ inch by 1.75 inches and inverted V's having a height and base

15 ¦ length of 0.5 inch.

16 ¦ The belt 12 is supported on four or more rollers 60,

17 ¦ 62, 64, and 66 as a moving endless belt which is relatively

18 ¦ flat over the top of the machine. Movement of the belt is gear ~, ~ provided by a/motor 68 that is coupled through a chain 70, for example, to a drive roller 60 which is held in a fixed 21 position. The roller 60, which is conventional and shown in more detai~ in FIG. 7, has several sprocket wheels 72 23 periodically located along the width of the belt. The truncated teeth in the sprocket wheels fit into the openings between adjacent transverse A wire portions. The teeth on 2~ the wheels72 are preferably shorter than the height of the 27 inverted V's 57, although this is not essential. The other 28 rollers 62, 64 and 66 may be the same shape as the drive 2~

,~.

: ..

1~L'3~30 1 roller 60. The belt 12 may be main~ained taut by connecting a 2 spring type tensioning means (not shown) to the other rollers 3 34, 36 and 38. Since the circu~t boards 14 are preferably : 4 stuffed with components ha~ing leads that are pre-trimmed to a length such as one-half inch, they only protrude about three-6 eighths inch below the underside of the circuit boards~ This 7 means that they extend only a short distance below the belt 12, - 8 if at all. It is not essential, however, that the leads be pre-: 9 trimmed ~o such a short length. The length of the belt between the solder wava 26 and roller 60 is set so that solder - 11 on circuit boards 14B is solidified before the boards 14B
12 reach the roller 60.
13 In a machine such as is shown herel there will be 14 some sag in the belt 12 between the rollexs 6G and 66, and possibly between opposite edges thereof in FIG. 2. It is 16 desirable that a circuit board be held as flat a~ possible as 17 it contacts the solder wave. In order to make the belt 12 18 taut in the d:irection of tra~el and in the transverse direction

19 as it passes through the solder wave 26, a pair of skids 46 and 48 are preferably located in the solder wave at opposite 2~ sides thereof (see FIGS. 2-4). Skids 46 and 4~ are parallel 22 to each other and to the arrow 15, and have top surfaces :. 23 thereof in a common plane which is parallel to and below the : 24 surface of the solder wave 26. The skids are spaced a distance d away from associated plates 40 and 42, so as to support the 26 belt 12 by contacting transverse A wires near the edges ~f the 27 belt (see FIGS. 2 and 3). The skids may be steel rods having 28 key ways in the center thereof that are fitted over the top of 2~

31 . _ ~ _ .

~ 38~

l the container 34 in FIGS. 3 and 4~ Alternatively, they may 2 have a rectangular cross section with the top-thèreof the vicinity of 3 rounded in/ the pot 28 to pre~ent molten solder in the wave 4 running out of the pot. Vertical baffles 74 may also be formed over the side and bottom of the skids to cause the molten 6 solder from the wave to fall back into the pot 28. The length 7 of the skids are such that they support at least ten transverse 8 A wires on either side of the wave. The skids are preferably 9 at least three times the length of the longest PC board to be processed. Alternatively, they may extend o~er substantially ll the full length of the belt on top of the machine. The 12 vertical height of the skids is selected to position the belt 13 so that the tops of V's 57 are just below the surface of the 14 wave 26 as the belt passes thxough it.: The top surfaces of skids 46 and 48 are preferably made o~ tool steel for wear 16 resistance. AlternativeIy~ they may be covered with a heat 17 resistant plastic to enhance sliding properties of the belt 18 on thern. The leading edges of the skids are rounded to 19 facilitate the belt moving freely up onto the tops thereof.
Although this invention is described in relation tc 21 a preferred embodiment thereof, variations and modifications 22 will occur to those skilled in the art without departing 23 from the spirit of this invention. By way of example, finger 24 structure may be employed to hold onto wires at the edge o~ the belt 12 over the length thereof to maintain it flat in the 26 solder wave 26 instead of employing the skids 46 and 48.
27 Such fingers could gradually fall away from the belt as it 28 approached the roller 60. Also, the machine may be modified .' ~0 31 _ 9 _ .: .

1 to include a pair of belts which are made of a solderable 2 material such as stainless steel. ~he first belt then carries 3 the boards through the fluxing operation and possibly the 4 first preheat operation. The fluxed circuit boards are then automatically trans~erred to a second belt that passes through the solder wave. Since the second belt is not fluxed, the ~ solder will have a lesser propensity to adhere to it. Further, 8 the projections 57 supporting the undersides of the circuit 9 boards above the major surface of the belt may be shaped other lQ than as in~erted V's. The projection may be generally curved 11 or be vertical wires. Alternatively, the belt may be entirely 12 devoid of such projections. The board will then rise slightly 13 as it moves into contact with the solder wave 26 so as to 14 expose the full underside of the board ~or soldering. Further, the carrier of circuit boards may be a plurality of endless 16 moving parallel wires81 in FIG. 8 that are made o~ a non-17 solderable material such as music wire. The wire tension and 18 the position of the solder wave 26 with respect to the end 19 support rollers 60 and 66 (not shown) in FIG. 9 in such a machine are adjusted so that the lowest point on the wires 21 is where they pass through the solder wave. The wires 81 may 22 be moved by a pair of drive rollers 83 and 85 which rotate in 23 opposite directions as shown in FIG. 9. Alternatively, the 2 carrier may be stationary wires 81 that are parallel to each other with fingers 87 of an elevated conveyor 89 (see FIG. 10) 26 pushing the boards 14 along the stationary wires 81 so that 27 the undersides of the boards move into contact with the solder 28 wave. Also, tracks 46 and 48 may be employed having facing 31 -lG -.

1: Ll384~0 : l sides thereof with portions cut away to form shoulders 46 2 and 48 (see FIG. 11) which support a circuit board thereon.
. These skids extend over the full length of the machine and the boards are pushed along the shoulders 46 and 48 , for example, ~ by fingers of an elevated conveyor as is shown in FIG. 10. The ;: 6 spacing between the skids is adjusted for the width of circuit 7 boards to be processed. Further, the top of the belt 12 8 between rollers 60 and 66 in FIG. 1 may be inclined at an ? 9 angle such as 6 , rather than being horizontal as is shown . 10 there. The scope o~ this invention is therefore to be deter-11 mined from the attached claims rather than from the aforementioned 12 detailed de riptions of preferred embodiments thereof.

l6 ' 1~
: 18 ~5 ' ~9 .'' ' ~0 - 11 - -. 31 , 32 ' ,"'" .

Claims (16)

What is claimed is:

1. In a wave solder machine for soldering leads of components stuffed in printed circuit (PC) boards to conductive patterns on the undersides of the boards and including means for producing a wave of molten solder having a width that is greater than a broad dimension of circuit boards to be soldered and hav-ing a length in a prescribed direction, the improvement comprising:
an elongated mesh belt for supporting a stuffed circuit board by the underside of the board, said belt extending through the solder wave in the prescribed direction with at least a por-tion of said belt being immersed in the solder wave; and means for moving said belt in the prescribed direction with protions of the underside of the board contacting said belt for causing at least a portion of the underside of the board to contact the molten solder wave as the belt passes through it.

2. The improvement according to claim 1 wherein said belt is formed in the shape of an endless loop, said belt being generally flat in a direction transverse to the prescribed direction.

3. The improvement according to claim 2 wherein said belt has a mesh size and shape that is sufficient for permitting the flow of solder into contact with the full breadth of the portion of the underside of the board that is available to con-tact the solder wave at any time.

4. The improvement according to claim 2 wherein said belt comprises a plurality of lengths of parallel wires, some of said wires having projections extending above the upper surface of the belt for contacting the underside of the circuit board and holding it above the upper surface of said belt.

5. The improvement according to claim 4 including means for causing at least several adjacent lengths of parallel wires of said belt that extend in a direction transverse to the prescribed direction and are proximate the leading edge of the solder wave to be generally in a common plane which extends through the solder wave.

6. The improvement according to claim 5 wherein said last named means comprises a pair of skids extending generally parallel to the prescribed direction, being immersed in the solder wave near opposite edges thereof, and having top surfaces extending under and contacting a plurality of parallel lengths of wires of said belt on both sides of the solder wave, the width of the belt being greater than the spacing between said skids.

7. The improvement according to claim 4 wherein said projections are generally inverted V's.

8. The improvement according to claim 7 wherein said belt is made of a nonsolderable material.

9. The improvement according to claim 8 wherein said belt is made of a material that is at least primarily titanium.

10. A wave solder machine comprising:
means for producing a wave of molten solder;
an elongated mesh belt for supporting stuffed printed circuit boards in the machine by the underside thereof, said belt being immersed in and extending through the solder wave in a prescribed direction; and means for moving the belt in the prescribed direction with portions of the undersides of circuit boards contacting said belt for causing the undersides of the boards to contact the molten solder wave as said belt moves through the solder wave and the boards move past it.

11. The improvement according to claim 10 wherein said belt is formed as an endless loop and comprises a plurality of lengths of parallel wires, said belt having projections formed on at least some of said wires and which extend above the upper surface of the belt for contacting the underside of a circuit board and holding it above the upper surface of said belt.

12. The improvement according to claim 11 including means for causing at least several adjacent lengths of parallel wires of said belt that extend in a direction generally trans-verse to the prescribed direction and are proximate the solder wave and on the leading edge thereof to be generally in a common plane which extends through the solder wave.

13. The method of soldering leads of components stuffed in printed circuit boards to conductive patterns on the underside of the boards comprising the steps of:
producing a wave of molten solder having a width that is greater than a broad dimension of a stuffed circuit board to be soldered;
supporting the stuffed circuit board on an elongated mesh belt with protions of the underside of the board contact-ing portions of the belt which is immersed in and extends through the solder wave in a prescribed direction; and moving the belt in the prescribed direction so as to progressively pass all of the underside of the board into con-tact with the molten solder wave as the belt passes through it.

14. The method according to claim 1.3 in which the belt is formed in the shape of an endless loop and is generally flat in a direction transverse to the prescribed direction;
the belt having a plurality of lengths of parallel wires, some of which have projections extending above the upper surface of the belt for contacting the underside of a circuit board and holding it above the upper surface of the belt.

15. The method according to claim 14 including the additional step of supporting a plurality of adjacent lengths of parallel wires of said belt that extend in a direction transverse to the prescribed direction and are proximate the leading edge of the solder wave for causing them to be generally in a common plane which extends through the solder wave.

16. The method according to claim 15 in which the plurality of wires are supported by a pair of skids extending generally parallel to the prescribed direction, being immersed in the solder wave near opposite edges thereof, and having top surfaces extending under and contacting a plurality of parallel lengths of wires of the belt on both sides of the solder wave, the width of the belt being greater than the spacing between the skids; and in which the belt is made of a nonsolderable material such as titanium.