Adjustable printed circuit board pallet

A pallet for holding a printed circuit board on a conveyor in a solder wave machine which applies molten solder to the underside of the printed circuit board for completing connections, includes a pair of longitudinally extending first and second bars mounted on a frame, the bars including a pair of oppositely disposed longitudinally-extending grooves for receiving the opposite side marginal edges of the printed circuit board. Each one of the grooves is substantially channel-shaped and extends to the rear end portion of the bars so that the printed circuit board may be slipped into the grooves at the rear end portion of the bars to insert the board in position. One of the bars is transversely movable relative to the frame, and the other bar is fixed in position on the frame, the movable bar being fixed releasably to the first bar in an adjusted position to the frame for accommodating various different sizes of boards. A transversely extending third bar mounted on the front portion of the frame includes a lengthwise extending groove for receiving an end marginal edge of the printed circuit board. The lower edge of the transversely disposed bar extends below the underside of the printed circuit board to cut into and spread out the wave of molten solder produced by the solder wave applying machine for distributing it over the underside of the printed circuit board.

The present invention relates to an adjustable printed circuit board 
pallet, and it more particularly relates to a pallet for holding printed 
circuit boards being conveyed through a solder wave machine, the pallet 
being adjustable to accommodate various different sizes of printed circuit 
boards. 
Pallets have been used for holding printed circuit boards in connection 
with solder wave machines, which are used to solder components onto the 
printed circuit boards. One type of solder wave machine includes a pair of 
spaced-apart conveyor chains for carrying the pallet which in turn carries 
a printed circuit board to be soldered past a series of three stations. 
The first two stations pre-heat the underside of the board and apply flux 
for cleaning the connections. A third station is the solder wave station 
which applies molten solder to the ends of the components extending 
through holes in the printed circuit board for soldering the connections 
to the conductors on the board. The solder wave station includes a pump to 
serve as a fountain to flow molten solder upwardly which then falls 
downwardly under the force of gravity so that the circuit board can be 
passed through the apex of the molten solder, which in turn then flows 
onto the underside of the printed circuit board. The molten solder is 
pumped upwardly in a recirculating manner, and after the conveyor moves 
the pallet past the last station, the pallet is then removed from the 
conveyor so that the completed printed circuit board may be removed from 
the pallet. For examples of such solder applying machines, reference may 
be made to the following U.S. Pat. Nos.: 3,056,370; 3,482,755; 3,605,244 
and 3,921,888. 
While such custom made pallets may be acceptable for some applications, it 
would be highly desirable to have an adjustable pallet which accommodates 
various different sizes of printed circuit boards. Attempts have been made 
to make the printed circuit board pallet adjustable by using spring loaded 
clamps to hold the printed circuit boards in position, but they have not 
been entirely satisfactory for some applications, since they have not held 
securely the printed circuit boards in position and were not convenient to 
use. In this regard, the circuit components are slipped into the holes in 
the printed circuit board and merely rest in position while the pallet is 
transported through the solder applying machine, whereby any jarring or 
vibration caused by the movement of the molten solder against the 
underside of the printed circuit board may dislodge the circuit components 
or otherwise cause improper or unsatisfactory connections to be made. 
Thus, it would be highly desirable to have a new and improved adjustable 
pallet which can accommodate various different sizes of printed circuit 
boards and which holds the printed circuit boards securely during the 
solder applying operation. Also, such a new and improved pallet should 
help apply the molten solder to the underside of the board in an evenly 
distributed manner. 
Therefore, the principal object of the present invention is to provide a 
new and improved adjustable printed circuit board pallet, which may 
accommodate various different sizes of printed circuit boards, and which 
holds the printed circuit boards in a secure manner during the applying of 
molten solder to the underside of the board. 
Another object of the present invention is to provide such a new and 
improved adjustable printed circuit board pallet which helps to evenly 
distribute the molten solder flowing to the underside of the printed 
circuit board. 
Briefly, the above and further objects of the present invention are 
realized by providing an adjustable printed circuit board pallet, which 
includes a pair of longitudinally extending first and second bars mounted 
on a frame, the bars including a pair of oppositely disposed 
longitudinally-extending grooves for receiving the opposite side marginal 
edges of the printed circuit board. Each one of the grooves is 
substantially channel-shaped and extends to the rear end portion of the 
bars so that the printed circuit board may be slipped into the grooves at 
the rear end portions of the bars to insert the board in position. One of 
the bars is fixed to the frame, and the other bar is mounted in a 
transversely movable manner, a device being provided for fixing releasably 
the movable bar in an adjusted position to the frame for accommodating 
various different sizes of boards. A transversely extending third bar 
mounted on the front portion of the frame includes a lengthwise extending 
groove for receiving an end marginal edge of the printed circuit board to 
provide for even greater stability in the manner in which the board is 
held in position. The lower edge of the transversely disposed bar extends 
below the underside of the printed circuit board to cut into and spread 
out the wave of molten solder for distributing it over the underside of 
the printed circuit board.

Referring now to the drawings, and more particularly to FIG. 1 thereof, 
there is shown an adjustable printed circuit board pallet 10, which is 
constructed in accordance with the present invention to hold printed 
circit boards 12, and which supports them while they are conveyed through 
a solder wave machine 14. The solder wave machine 14 generally comprises a 
conveyor 16 which includes a pair of parallel spaced-apart chains 18 and 
20 for supporting the pallet 10 therebetween. Sprockets 22 are driven by a 
source of power (not shown) to move the pair of chains for transporting 
the printed circuit board carrying pallet 10 past a series of stations 
disposed between the chains 18 and 20. A pre-heat station 24 and a fluxer 
station 26 heat the underside of the printed circuit boards 12 and apply 
flux for cleaning the circuit component connections. A solder wave station 
28 supplies molten solder to the underside of the pre-heated and cleaned 
printed circuit boards 12 which have circuit components to be soldered 
thereto. The solder wave station 28 may include a fountain (not shown) for 
spraying molten solder upwardly into the path of travel of the pallet 10 
so that circuit component leads extending through holes in the printed 
circuit boards 12 may be soldered to conductors on the printed circuit 
boards. It should be understood that the adjustable printed circuit board 
pallet 10 of the present invention may be used with different types and 
kinds of solder wave machines. For example, the pallet of the present 
invention is adapted to be used with machines employing different types 
and kinds of conveyors. 
The adjustable pallet 10 generally comprises a rectangular frame 31 having 
a fixed longitudinally extending bar 33 and a pair of movable 
longitudinally extending bars 35 and 37 which are adjustably fixed in 
position to accommodate various different sizes of printed circuit boards 
as hereinafter described in greater detail. As shown in FIGS. 2, 3 and 5 
of the drawings, the fixed bar 33 has a longitudinally extending groove 39 
extending throughout its length for receiving side marginal edges of the 
printed circuit boards 12, and similarly the intermediate movable 
longitudinally extending bar 35 has a longitudinally extending groove 41 
extending throughout its length for receiving the opposite side marginal 
edges of printed circuit boards 12, the grooves 33 and 35 being arranged 
in the same plane in opposite confronting relationship relative to one 
another. Similarly, a groove 43 extending throughout the length of the 
movable intermediate bar 35 receives the side marginal edges of printed 
circuit boards 12 so that printed circuit boards 12 may extend from 
opposite sides of the intermediate movable bar 35 in a common plane, and a 
groove 45 in the other movable bar 37 extends throughout the length of the 
bar 37 for receiving the opposite side marginal edges of the printed 
circuit boards 12, the grooves 43 and 45 being disposed in confronting 
relationship in a common plane with the grooves 39 and 41 to support the 
printed circuit boards on both sides of the intermediate bar 35 in a 
common plane. As hereinafter described in greater detail, the movable bars 
35 and 37 may be positionally adjusted relative to the fixed longitudinal 
bar 33 to accommodate various different widths of printed circuit boards. 
The printed circuit boards are slipped into the pairs of grooves and 
arranged in abutting relationship so that the pallet 10 can accommodate 
various different lengths of printed circuit boards or a series of shorter 
printed circuit boards positioned in abutting end-to-end relationship as 
illustrated in the drawings. 
Considering now the frame 31 in greater detail with reference to FIGS. 2, 
3, 4 and 5 of the drawings, the frame 31 includes a front frame member 47 
fixed to the top edges of the front portions of a pair of 
oppositely-disposed parallel spaced-apart longitudinally extending side 
frame members 49 and 50 by means of screws 52. A rear frame member 54 is 
secured by screws 56 to the top edge of the rear portions of the side 
frame members 49 and 50 to cause the frame 31 to have a rectangular shape. 
A pair of downwardly depending pins 58 and 60 extend from the underside of 
the front portions of the side frame members 49 and 50 to engage the 
corresponding chains 20 and 18 of the conveyor 16 so that the conveyor 16 
can pull the pallet 10 over the stations of the solder wave machine 14 of 
FIG. 1. 
In accordance with the present invention, for the purpose of facilitating 
the distribution of the molten solder to the underside of the printed 
circuit boards 12, as best seen in FIGS. 2, 4 and 5 of the drawings, an 
angle iron bar 62 has a horizontal portion 62A which is fixed to the 
underside of the front transversely extending frame member 47 by means of 
a series of screws 64. A groove 65 in a vertical portion 62B of the angle 
iron bar 62 receives the front end portions of the printed circuit boards 
12 for greater stability in holding them in position. The groove 65 is in 
the same common plane with the grooves in the longitudinally-extending 
bars. The groove 65 is disposed near the bottom edge of the vertical 
portion 62B of the bar 62 so that the bottom edge of the vertical portion 
62B serves as a plow to cut into and spread out the wave of molten solder 
for distributing it over the underside of the printed circuit boards 12. 
Thus, the bar 62 serves the dual purpose of more firmly securing the 
printed circuit boards 12 in position on the pallet 10 and of distributing 
the molten solder to the underside of the printed circuit boards. 
In order to make the longitudinal bars 35 and 37 to be movable, an 
elongated slot 66 (FIG. 4) in the vertical portion 62A of the front bar 62 
extends transversely to receive a pair of set screws 68 and 70 fastened 
into the front end edges of the respective longitudinal bars 35 and 37. As 
shown in FIGS. 2 and 3 of the drawings, a pair of cap screws 72 and 74 
extend through an elongated slot 76 in the rear frame member 54 and are 
tightened into tapped holes in the upper edges of the rear portions of the 
movable longitudinal bars 35 and 37, washers 78 and 80 being disposed 
between the rear frame member 54 and the respective heads of the screws 72 
and 74. 
A screw 82 extends through the rear frame member 54 and is tightened into a 
tapped hole in the top edge of the rear portion of the fixed 
longitudinally-extending bar 33 to fix it in place within a recess 84 in 
the rear portion of the bar 33 to make the frame member 54 flush with the 
rear portion of the bar 33. Screws 86 extend through holes in the angle 
iron bar 62 into tapped holes in the front end edge of the fixed bar 33 to 
secure it in place. A complementary-shaped recess 88 in the upper edge of 
the rear portion of the intermediate movable bar 35 receives the rear 
frame member 54 at the elongated slot 76 to make the rear frame member 54 
flush with the rear end portion of the intermediate movable bar 35. 
Similarly, a complementary-shaped recess 89 in the top edge of the rear 
portion of the other movable bar 37 makes the rear frame member 54 flush 
with the rear portion of the movable bar 37. As best seen in FIGS. 2 and 5 
of the drawings, a complementary-shaped recess 91 in the upper front end 
portion of the intermediate bar 35 receives the front frame member 47 to 
make it flush therewith. Similarly, front recesses 93 and 95 in the top 
edge portions of the front end portions of the bars 93 and 95 enable the 
front frame member 47 to be flush therewith. 
In order to prevent any relative rotation between the movable bars 35 and 
37 and the angle bar 62, a pair of forwardly extending lips or flanges 97 
and 99 project forwardly from the front end portions of the movable bars 
35 and 37 to fit under the vertical portion 62A of the angle bar 62. As a 
result, the movable bars 35 and 37 are fixed securely in place by the 
screws 68 and 70. It will become apparent to those skilled in the art that 
instead of employing the lips 97 and 99, a second elongated slot (not 
shown) similar to the slot 64, may extend through the vertical portion 62A 
of the angle iron 62 for receiving a second pair of screws (not shown). 
It should be understood that the intermediate longitudinally-extending bar 
35, if desired, may be removed from the pallet 10 to accommodate certan 
sizes of printed circuit boards. For example, printed circuit boards (not 
shown) of a greater width than the printed circuit boards 12 shown in the 
drawings could be held in place between the fixed longitudinally-extending 
bar 33 and the movable bar 37, whereby the intermediate 
longitudinally-extending bar 35 would be removed from the pallet 10 by 
removing the screws 72 and 68. 
All of the parts of the pallet 10 may be composed of a rigid material, such 
as metal. The pallet 10 may, for example, be composed of aluminum, and the 
entire pallet 10, except for the screws and washers, should be impregnated 
with Teflon for facilitating removal of solder from the pallet 10. The 
pallet of the present invention may alternatively be composed of stainless 
steel or titanium, which do not require impregnation with Teflon since 
these materials are readily cleanable. 
The grooves for receiving the side edges of the printed ciruit boards are 
complementary shaped relative to the shape of the printed circuit boards 
and are thus channel shaped. As shown in FIG. 3 of the drawings, the 
movable longitudinally-extending bars are positioned such that the side 
edges of the printed circuit boards do not completely enter all of the way 
into the grooves to provide clearance spaces so that when the boards are 
heated they can expand without buckling. The adjustments made to the 
longitudinally-extending movable bars 35 and 37 can be made by unskilled 
personnel. 
While the present invention has been described in connection with a 
particular embodiment thereof, it will be understood that many changes and 
modifications of this invention may be made by those skilled in the art 
without departing from the true spirit and scope thereof. Accordingly, the 
appended claims are intended to cover all such changes and modifications 
as fall within the true spirit and scope of the present invention.