Device and Method for Repairing Conductor Path Breaks by Welding

The invention concerns a device for the repair of conductor path interruptions or breaks on printed circuit boards by means of microwelding.

In the case of new generation printed circuit boards, the conductor paths no longer run in a straight line, but rather are designed meander-like in trapezoidal conductor paths. The conductor paths produced by means of etching have, for example, a height of 30 .mu.m and a width of 120 to 150 .mu.m. The base length of a trapezoid is, for example, 1.20 mm.

In the case of the manufacturing process, interruptions can arise in the conductor paths. Since the printed circuit boards after placement of components are subjected to a soldering process, the repairing of the conductor paths must be carried out with a method whereby it is assured that the repair points suffer no damage as a result of the temperature arising by means of the soldering, and that the connections do not break again. Such a method is micro-resistance welding. In the magazine Feinwerktechnik, 75, 1971, Pamphlet 5, pp. 201-206, incorporated herein by reference, a method is described whereby through means of micro-resistance welding with a constant voltage device and gap electrodes with the use of nickel strips or wires, constricted or broken conductor paths are repaired on through-connection printed circuit boards.

In the case of straight conductor paths, the interruption was bridged by means of a suitable repair strip which was soldered on at both sides of the interruption one after the other by means of emplacement electrodes. The positioning thereby proceeded by means of a separate suction nozzle which was removed after the production of the first spot weld.

It is an object of the invention to design a device for the repair of conductor path interruptions on printed circuit boards which simultaneously makes possible the correct positioning of the parts to be welded and also welds, to thereby simplify the known method. The problem forming the basis of the invention is solved with a device for the welding process of a specific shaped part from a foil strip at both sides of a conductor path interruption, wherein a three-part electrode system is provided which consists of a central inside electrode equipped with a vacuum end for the suctioning of the shaped part, and around which two semicircular-shaped outside electrodes sit concentrically. These electrodes in each case are separated from one another electrically by means of an air gap and further are spring suspended mechanically, independently of one another. With this device it results that simultaneously the inside electrode can take up the shaped part by means of vacuum intake air and thus can both contribute to the positioning and the welding. In this manner, no additional suction nozzle is required.

According to a further development of the invention, the three electrodes are connected to the secondary circuits by two current impulse sources. With releasing of the welding pulses which are separated chronologically from one another via a special clock pulse generator, the inside electrode functions as two electrodes. This has the advantage that the two connection points required for the repair can be carried out in one operation.

According to a further design of the invention, the inside electrode and the outside electrodes are movable independently of one another and the inside electrode is moved down ahead of time. This permits using the inside electrode for positioning purposes.

FIG. 1 shows an electrode arrangement in a perspective view with current impulse sources and a shaped part for repairing an interrupted conductor path;

FIG. 2 shows the electrode arrangement in a side view partially in section illustrating the shaped part and also the printed circuit board having an interrupted conductor path.

In the Figures, a central inside electrode 1 with a bore hole 2 for a vacuum end is shown. Concentrically around this inside electrode are arranged two outside electrodes 3,4. The inside electrode 1 is connected on one side to the outside electrode 3 with a current impulse source 5, and on the other side to the outside electrode 4 with a current source 6. An air gap 7 separates the three electrodes electrically and mechanically from one another. On the underside of the inside electrode, a shaped part 8 of a foil strip is sucked on. All three electrodes are spring-suspended independently of one another with the springs 9, 10 and 11. The arrows inside of the electrodes in FIG. 2 indicate the direction of force. In FIG. 2, there is also depicted a conductor path 13 with an interruption 14 on a printed circuit board 12.

For repairing the interruption, a shaped part designed specifically for the interruption is punched out of a foil strip. The inside electrode picks up the shaped part by means of a vacuum air intake from a punch which is not shown. By means of the protruding inside electrode 1, the shaped part 8 can be lowered onto and partially cover the conductor path 13 which is to be repaired. The mechanically generated electrode force holds the shaped part positionally correct on the repair location. The outside electrodes which follow in each case contact the ends of the shaped part. With releasing of welding pulses separated from one another chronologically, the inside electrode functions as two electrodes.

Although various minor modifications may be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of my contribution to the art.