Patent GB-1370211-A (GB)
Title: Automatic bonding apparatus with multiple bonding heads
IPC: H05K13/06
Filed: 1972-01-14
Abstract: 1370211 Welding by pressure INFOREX Inc 14 Jan 1972 [27 Jan 1971] 1954/72 Heading B3R [Also in Division G3] Apparatus for simultaneously wiring a plurality of circuit boards in a point-to-point wiring operation comprises a plurality of soldering heads of the type having a solder tip 201 with an opening therethrough through which insulated wire may be drawn from a supply reel 12, a table 14 for supporting a circuit board beneath each head, a digital controller 15 operating under control of a stored programme, e.g. a punched tape, for positioning the table so that the soldering heads become aligned with the pads to which connections are to be made and a control system 19 ... 22 for each head for automatically lowering the head into contact with a pad and applying heat to vaporize the insulation and solder the wire to the pad and then raising the head again. Each soldering head is mounted on a cam-operated pivotally supported lever and the supply of electricity to the soldering tip is arranged to give an initially high temperature, to ensure vaporizing of the insulation and is reduced once electrical connection is established between the wire and soldering tip. If this electrical connection is not established the heating is reduced after a time delay in any case to prevent damage to the circuit board. The soldering tip has a supply of nitrogen to cool and clear the wire opening. Each head carries a probe 214 which is lowered after each bonding operation into contact with the pad to check for electrical continuity between the probe and wire. If electrical connection has not been made in the first soldering operation the soldering head is automatically lowered again to make a second soldering attempt and the table 14 cannot be moved to the next position until this has been achieved. Each soldering head also carries a wire gripping device comprising solenoid and spring-operated gripping washers (Fig. 2E, not shown) which tension the wire extending from the soldered connection when the head is raised; the wire extending from the connection is thereby pulled so as to determine whether a mechanically sound connection has been made. Immediately after a soldering operation has been carried out a supply of cooling air is directed on to the connection. In order to ensure that short circuits do not arise between wires extending between the soldered connections, e.g. due to breaks in the electrical insulation a test is applied for electrical continuity between the soldering tip and the wire being drawn through the tip during movements of the table 14; to this end the bus-bars 202 (203) which during soldering serve to supply electricity to the tip 201, are earthed and a suitable voltage applied to the insulated wire. At the end of a wiring network a solenoid-operated cutter 221 severs the wire between the last pad and the soldering tip and when the soldering head is raised the probe 214 is again lowered into contact with the pad to establish that electrical connection no longer exists between the pad and the wire in the soldering tip i.e. to check that the cutting operation has been successful. The digital controller 15 which controls movements of the table 14 may have provision for carrying out a position check by returning the table to a home position. Electrical relay circuits are described for the control systems for ensuring that bonding, testing and recycle bonding, if necessary, are carried out in correct sequence and in proper conjunction with movements of the table 14 under the control of the controller 15. The latter has three relay actuated switches (Fig. 3, not shown) controlled by the punched tape which initiate the functions of bonding, cutting the wire at the end of a net, testing the cut, and the periodic position check.