Patent GB-1036167-A (GB)
Title: Improvements in or relating to semiconductor devices
IPC: H01L23/04
Filed: 1964-03-06
Abstract: 1,036,167. Semi-conductor devices. STANDARD TELEPHONES & CABLES Ltd. March 6, 1964, No. 9636/64. Addition to 1,023,531. Heading H1K. A semi-conductor wafer is provided with a ledge on at least one edge to enable its attitude to be sensed. The wafer, which has an insulating layer on its surface carrying a contact graded from an adherent metal adjacent the layer to a soft solderable metal remote from it, may be made as follows. Intersecting sets of parallel grooves are cut, preferably by a slow chemical etch, in one face of an N-type silicon wafer which is then surface oxidized in steam or oxygen. NPN planar transistors are next formed in the islands between the grooves as described in Specification 1,022,366. After depositing aluminium or nickel in apertures in the insulating oxide layer to contact the base, emitter and collector zones respectively graded contacts are provided extending from the deposits to large areas marked 10, 11, 12 in Fig. 6. The contacts may be graded from manganese to silver or gold to chromium and are tinned by dipping in molten lead-tin eutectic or silver solder. The wafer is next divided into single devices by cutting along the grooves using a rotary saw or an ultrasonic or spark erosion cutter in such a way that each device is rectangular and has ledges along three of its four edges (Fig. 6). The devices are mechanically mounted on headers of the type described in Specification 1,036,165 as follows. They are first shaken up a helical or linear ramp by a vibratory mechanism to the position shown in Fig. 9a (not shown). Any devices which are upside down are rejected by a tapered member on the ramp, Figs. 8a and 8b (not shown). A correctly positioned device by obscuring photo-cell aperture 25 while leaving photo-cell aperture 26 clear causes turret 27 to rotate, pushing the device into a semicircular channel, Fig. 10 (not shown), down which it slides into an inverted position where it is picked up by a suction head (Fig. 11, not shown). Incorrectly positioned devices are rejected by a reverse movement of the turret. The device 23 on the suction head is positioned over a header 31 brought up on a conveyer and the header wires soldered to the contacts with which they are in register. Excess solder runs on to the oxide coated ledges. After coating with silicone resin the device is mounted in a can or plastics encapsulation as described in Specification 1,036,165. In another embodiment, a planar diode wafer with ledges on all four edges is mounted in a glass envelope between two rigid metal plugs or between such a plug and a resilient contact member as described with reference to Figs. 15-18 (not shown). In each case the ledge by catching excess solder reduces the possibility of a short-circuit. In arrangements with contacts on both wafer faces alignment ledges may be provided on both faces. Instead of silicon germanium and gallium arsenide may be used for the wafers in which case the insulating layer is of resin or deposited silicon oxide. The invention may be applied to silicon controlled rectifiers, tinned diodes, and solid circuits, any of which may employ triangular or circular wafers, and be mounted on headers as described in Specifications 870,599 and 1,026,164.