Method for making circuit boards with die stamped contact pads and conductive ink circuit patterns

Printed circuit boards have copper contact pads cut from copper foil and bonded to the circuit board, followed by printing circuit patterns of conductive ink on the board, the pattern connecting with the contact pads. The contact pads are cut from a copper foil strip fed with the circuit board beneath a die. Bonding of the contact pads follows, then printing of the circuit patterns. Boards can be formed from strip material in which case the individual boards are cut from the strip material.

This invention relates to circuit boards with die stamped contact pads and 
conductive ink circuit patterns, and to a process for making such boards. 
Circuit boards are made using techniques such as using porcelainized steel 
blanks with screened silver inks which are fired; copper patterns on 
dielectric boards; polymer thick films on dielectric boards. Connections 
can be made by soldering for the first two examples, while a connector is 
required for polymer thick films as these are not solderable. For copper 
patterns on dielectric boards, contact areas are generally produced by 
plating on to the conductor patterns at desired places. 
To reduce the cost it has been proposed to use conventional printed circuit 
board copper patterns, screen printed with conductive inks at positions 
where contact pads are required. A further reduction in cost could be 
obtained by avoiding the preparation of the copper patterns and printing 
the pattern directly on the board. However, this would require a connector 
to connect the ink circuitry to components or other boards or devices. 
The present invention proposes the die stamping of contact pads on to the 
dielectric board, at desired locations, followed by screen printing of 
conductive ink patterns. Typically, a strip of copper is fed over boards; 
the contact pads are die cut from the copper strip and pressed onto the 
boards, with the perforated strip wound up; the copper pads are bonded to 
the boards with heat and pressure; conductive ink patterns are then 
printed on the boards, connecting with the contact pads. The copper strip 
hs an adhesive on its lower side and this adhesive is cured by the heating 
and pressure. While the boards can be singly fed, with suitable locating 
means, it will usually be more effective to feed the boards in strips, 
with punching or shearing of finished boards from the strips.

In the circuit boards illustrated in FIGS. 1 and 2, the dielectric base or 
board is indicated at 10, circuit patterns at 11, formed by copper, with 
contact pads at 12. The contact pads 12 usually have holes 13 therethrough 
for reception of pins of a connector, or passage of wires, usually 
afterwards soldered to the pads 12. Contact areas for push-button keys are 
formed at 14, as by printing conductive inks at areas indicated at 15. It 
is often very difficult to obtain accurate register between the conductive 
ink areas 15 and the copper pattern at those areas. Clearances between the 
various areas 15 at a position 14 are very small, as are the clearances 
between the copper areas at these positions and short-circuits can occur. 
FIG. 3 illustrates a board which is similar to that of FIG. 2, but with 
contact pads 12 made slightly elongate. The pads are applied by die 
cutting or stamping from copper film or strips, and the circuit patterns 
11 are formed by printed conductive ink. Holes 13 can be provided in die 
pads 12. The contact areas 14 in FIG. 2 are formed by printing ink on to 
copper. In a board as in FIG. 3, the contact areas are formed at the same 
time as the patterns 11 are formed. Thus the need for accurate register 
between contact areas and conductor patterns is avoided. 
A process, or method, of forming circuit boards is illustrated in FIGS. 
4(a) to 4(d). In FIG. 4(a), a strip of dielectric material 20 is fed along 
on a support surface, holes 21 in the strip acting as locating means. A 
strip of copper foil 22 is fed from a feed roll 23 beneath a press 24 with 
a die 25. The strip has an adhesive on its lower surface. The die 25, 
which may be heated, stamps out contact pads from the copper foil and 
presses them on to the strip 20, the pads seen at 26. The scrap, 
perforated strip is wound up on a take-up roll 27. 
In FIG. 4(b) the strip 20 passes beneath a press 30 having a heated pad 31 
which presses on the pads 26 and cures the adhesive. In FIG. 4(c) a 
printing machine 34 prints the circuit pattern on the strip 20, the 
circuit patterns indicated at 35. In FIG. 4(d) the strip passes beneath a 
blanking press 37. The press 37, in addition to blanking out the circuit 
boards, indicated at 38, can also form any holes required in the circuit 
board. 
The strip of dielectric material is of a length sufficient to produce a 
predetermined number of circuit boards. The strips are fed beneath the 
various presses and other apparatus by means of a conventional stepping 
mechanism which feeds the strip in steps, a step being equal to the pitch 
of holes 21 for example. The presses 24, 30, and 37 and printing machine 
34 are shown electrically operated, the operation being readily controlled 
by a central control. Thus the strip 20 is moved on pitch, then the 
various presses and printing machine actuated, then the strip advanced one 
step, and so on. However, it would be possible to actuate the presses and 
printing machine hydraulically or pneumatically. The heating pad 31 would 
normally be heated electrically. If desired, some form of heating of the 
printed strip, after printing of the circuit pattern, can be provided. 
Various advantages result from the invention. The die-press application of 
the contact pads is simple and accurate. The step of printing the 
conductive ink circuit patterns is also simple and inexpensive. No very 
accurate register between the printing of the circuit patterns and the 
contact pads is required and shorting between adjacent areas of a circuit 
pattern is avoided. The overall cost is reduced. The scrap from the 
contact pad forming foil has a high resale value as it is clean and has 
very little contamination. It is also possible to apply the invention to 
individual precut circuit boards. It would be necessary to provide the 
circuit boards with some locating menas, such as holes, to ensure that the 
individual boards are fed consequtively along beneath the various 
machines. In this arrangement, the blanking press may not be required, or 
may be required for forming holes only.