A solder leveller comprises a solder bath into which a printed circuit board can be dipped to be preliminarily tinned. A pair of upright laterally acting jaws are adapted along an extended part of their length to hold the board at its opposite side edges and operate to insert in and withdraw the board from the bath. An air knife removes excess solder. The jaws are guided centrally of the bath by engagement of the side faces with the air knife nozzles which act as fixed guides.

THE FIELD OF THE INVENTION 
A solder leveller is apparatus for coating exposed metal--normally 
copper--on printed circuit boards, and similar elements--particularly for 
supporting electronic components--hereinafter referred to as "boards", 
with solder preparatory to connection of components thereto. A solder 
leveller normally comprises a solder bath, into which a board to be 
soldered is lowered, and means for levelling solder deposited on the board 
as it is withdrawn from the bath. 
A solder leveller of the type with which the present invention is concerned 
includes means for gripping the board, inserting it into the solder bath 
and withdrawing it therefrom. 
THE BACKGROUND OF THE INVENTION 
The solder levelling means is intended to provide a substantially uniform 
thickness of solder on the exposed copper and to unblock any holes through 
the board which might otherwise be blocked by solder. The levelling means 
may be arranged to direct hot liquid at the board as it is withdrawn from 
the solder. However, it is presently preferred to direct hot air at the 
board by means of so called "air knives" for levelling the solder as the 
board is withdrawn from the solder bath. 
Such a solder leveller is described in UK Patent Specification No. 
1,457,325 and equivalent U.S. Patent Specification No. 3,865,298 (U.S. 
Atomic Energy Commission). This prior leveller includes means for 
deflecting hot air from the air knives away from the surface of the molten 
solder in the solder bath. These deflection means can in practice be 
dispensed with, particularly where the molten solder in the bath is 
continuously recirculated whereby any flux and/or dross (oxidized solder) 
is carried by the flow of the molten solder away from the area of the 
surface of the molten solder through which the board is to be inserted. 
When a board is being treated in such a recirculating solder leveller, it 
may be displaced from its preferably central position in the solder bath 
to the extent that it is scratched on withdrawal from the bath. Scratching 
is likely to result in the board being reject. Such scratching is believed 
to result from contact with the walls of the solder bath. 
The usual manner of supporting a board for insertion in the bath is from 
above. This can lead to the possibility of the board being deflected by 
the flow of solder to one side of the bath and contacting the 
corresponding side wall whereby on withdrawal of the board it scrapes 
along the side wall and becomes scratched. 
Accordingly, in my UK Patent No. 2,151,528 (which has an equivalent U.S. 
Pat. No. 4,599,966) I describe and claim a solder leveller including means 
for recirculating molten solder to and from the solder bath which 
comprises parallel spaced apart side walls, end walls and a bottom wall, 
the recirculating means comprising a plurality of side wall ducts having 
side wall ports therein one above another to direct a flow of solder 
against opposite sides of a board inserted in the bath, an elongate bottom 
wall duct extending along the bottom wall of the bath, the bottom wall 
duct having ports communicating with the lower ends of the side wall 
ducts, and means for pumping solder through the elongate bottom wall duct, 
the side wall ducts and the bath, in such manner that the flow of solder 
in the solder bath biasses a board inserted therein away from side walls 
of the solder bath. 
However, although this leveller has proved successful, in practice, it is 
normally necessary to augment the effect of the side wall ducts on the 
centring of the board in the solder bath with guides for guiding the edges 
of the board, if only to ensure that as the board is initially lowered 
into the solder bath it is centred. These guides can cause problems. In 
particular, they interfere with the deposit of solder onto the edge 
regions of circuit boards. 
Irregularly shaped boards are awkward to process because part of their edge 
portions are located by the guides whilst other parts do not extend as far 
as the guides and are not located. These problems are aggravated with 
smaller boards. 
Small boards provide an additional problem in that they may have no spare 
surface area at which a clamp or other holding means active at the top 
edge of the board can hold them. 
THE INVENTION 
Accordingly, I have perceived the need for an improved solder leveller in 
which these problems of guiding and gripping of the board are alleviated 
and it is the object of the present invention to provide such a leveller. 
In the solder leveller of the invention the gripping, insertion and 
withdrawal means comprises a pair of upright, laterally acting jaws 
adapted along an extended part of their length for holding a board at its 
opposite side edges; means for closing the jaws to grip the board; and 
means for supporting the jaws above the solder bath. 
Advantageously, the jaws have concave board holding faces, the preferred 
concave face shape being a V-groove shape extending along the jaws. 
The lower, free ends of the jaws may extend unguided into the solder bath; 
but fixed guides extending transversely of the jaws' travel are preferably 
provided. Since the jaws are relatively inflexible, the guides can be 
restricted to act at one height only and are conveniently in the form of 
the opposite edges of air knife nozzles, when the latter are provided in 
the solder levelling means. 
Conveniently the jaws are mounted on a laterally extending cross member, 
each jaw being movable along the cross member. This arrangement enables 
one jaw to be moved through a predetermined stroke for on the one hand 
opening the jaws to release a board and on the other hand closing the jaws 
to grip a board; whilst the other jaw can be moved for overall adjustment 
of the bight of the jaws. In an alternative one jaw could be fixed whilst 
the other is both movable for opening and closing and for adjustment. 
The molten solder in the solder bath must be hotter than the eutectic 
temperature of tin-lead, i.e. 183.degree. C. This results in a 
considerable bowing of wide printed circuit boards contained widthwise by 
the jaws, when heated from ambient temperature on insertion into the 
molten solder. Such bowing can result in the board fouling the air knives 
on withdrawal from the solder. Accordingly the actuator arranged to close 
the jaws to the board may be arranged to relax them to a small extent 
prior to withdrawal of the board. Alternatively a separate actuator for 
the adjustable jaw may be provided to relax it. 
To help understanding of the invention, a specific embodiment thereof will 
now be described with reference to the accompanying drawings.

THE PREFERRED EMBODIMENT 
The solder leveller has a solder bath 1, including insulation, means for 
heating of solder in the bath and for circulating solder to and from the 
bath together shown in outline at 2 since these features are conventional. 
So called "air knives" 3 are provided with nozzles 4 oppositely arranged 
the one slightly above the other. The air knives are provided in an upper 
housing 5 which can be lifted about a pivot point 5' for access to the 
free surface 6 of the molten solder 7. Again these features are 
conventional. 
A rectangular, steel column 8 extends up from the housing 5 and 
accommodates a rodless cylinder 9. The cylinder's drive member 10 extends 
rearwardly out of a slot (not shown) in the column. A pair of knife-edge 
rails 11 are fixed along the opposite sides 12 of the column 8. A yoke 13 
surrounds the column and carries rollers 13' inside the side parts of the 
yoke, the rollers 13' engaging and being guided by the rails 11. The 
rodless cylinder's drive member 10 is connected to the yoke, whereby the 
yoke 13 can be moved up or down the column. 
Attached to the front of the yoke 13 is a transverse, knife-edge guide rail 
14. Two jaw carriers 15.sub.r, 15.sub.1 are mounted for lateral movement 
along the guide rail 14, via two upper and two lower Vee rollers 16 each. 
Elongate, downwardly tapering jaws 17.sub.r, 17.sub.1 are bolted one to 
each carrier. The jaws have Vee grooves 18 in opposed edges. The bottom 
end of each of these grooves is closed to prevent a board only loosely 
held from dropping from the grooves. 
To the right of the yoke 13, a rib 19 extends behind the guide rail 14, the 
rib 19 having a series of apertures 20 in its upper surface and spaced 
along its length. The right hand carrier 15.sub.r has a pair of flanges 21 
extending forwardly with a horizontal screwed shaft 22 fixed between them. 
The shaft carries a thumb nut 23 and a clevis 24 embracing the nut. An 
upper extension 25 of the clevis passes over the guide rail 14 and 
supports a plunger 26 which is spring biassed into a selected one of the 
apertures 20. Movement of the plunger from one aperture to the next 
provides coarse adjustment of the position of the carrier 15, whilst 
screwing of the nut 23 along the shaft 22 provides fine adjustment of the 
carrier and of the lateral position of the right hand jaw 17.sub.r. 
To the left of the yoke 13 a pneumatic actuator 27 is secured behind the 
guide rail 14. The rod 28 of the actuator is secured to a finger 29 
crossing behind the rail 14 and fixed to the left hand carrier 15.sub.1. 
The actuator has a short stroke for moving the left hand jaw 17.sub.1 
between an open position moved away from the other jaw and a closed 
position moved towards the other jaw for gripping a board 30. 
FIG. 1 shows the transverse guide rail 14 raised and raising with it the 
jaws 17.sub.r, 17.sub.1. In this position, the right hand jaw 17.sub.r is 
adjusted until the bight of the jaws is such that on operation of the 
actuator to open the jaws, the circuit board 30 can be introduced at its 
edges into the Vee grooves 18 and that on subsequent closing of the jaws 
the board is tightly gripped at its side edges. The printed circuit faces 
of the board are not mechanically obscured by the jaws which abut the 
board's edges, at the right angle corners between the faces and the side 
edges, via the angled faces 31 of the jaws--see FIG. 4. For insertion of 
the board into the jaws' grooves, one side edge can be inserted into one 
jaw groove and the other guided in between the operator's grooved thumb 
and fore finger gripping the board and jaw on opposite sides. In an 
alternative a rearwardly withdrawable stop 32, shown dashed in FIG. 4, may 
be provided adjacent the jaw 17.sub.1 for the board to be abutted against 
after insertion into the groove of the jaw 17.sub.r. The stop guides the 
board into alignment with the groove of the jaw 17.sub.1. The stop may be 
withdrawable by an actuator ganged to the actuator 27 so that it is in 
position only when the jaws are open and is withdrawn at all other times 
There is no requirement for the board to be of regular rectangular shape 
for it to be gripped in the jaws' V-grooves. Thus irregularly shaped 
boards can be processed. This is a significant advantage of the invention. 
Once the board is gripped, the rodless cylinder is actuated to insert the 
board into the solder bath. The bottom ends 33 of the jaws remain between 
the air knives' nozzles even when the jaws are fully withdrawn upwardly, 
whereby the jaws are permanently guided to remain in the centre of the 
solder bath. After the conventional dwell time, the jaws are withdrawn 
upwards with the exposed copper on the board now tinned with solder The 
actuator 27 is operated and the board removed. If provided, the optional 
stop 32 can be programmed not to be brought forward on opening of the jaws 
after insertion so as not to mark the tinned board. 
To avoid deposit of solder on the jaws, they are conveniently of titanium. 
Although the solder does not "wet" the jaws, it flows to the very edges of 
the board supported by the jaws' grooves so that the copper of the board 
is wetted and tinned right up to the very edges. 
VARIANT 
In FIG. 5, the rib 19 is replaced by a central portion 50 connecting the 
guide rail 14 to the yoke 13 and a movable portion 51 behind the right 
hand limb of the guide rail 14. The portion 15 is slidably secured to the 
guide rail by means of a slide 52 and is arranged to be movable axially of 
the guide rail under control of a further pneumatic actuator 53 to enable 
the jaws to be incrementally opened whilst the board is immersed in the 
solder. This accommodates expansion the board due to heating on immersion 
so that consequent bowing of large boards does not cause them to foul the 
air knives nozzles It is envisaged that a single incremental movement for 
any size of board over 300 mm wide will suffice. Nevertheless, the 
incremental movement may be arranged to be proportional to the bight of 
the jaws. 
An advantage of the solder leveller is that it can be used for tinning 
copper contact pads of boards in the form of ceramic substrates, which 
have been virtually impossible to process with conventional solder 
levellers.