Patent GB-1031939-A (GB)
Title: Method and apparatus for assembling semi-conductor devices
IPC: H01L21/00
Filed: 1964-03-20
Abstract: 1,031,939. Machines for making semiconductor devices. STANDARD TELEPHONES & CABLES Ltd. March 20, 1964 [April 23, 1963], No. 11850/64. Headings H1J and H1K. A method of manufacturing a semi -conductor device comprising a flexible whisker containing or coated with a significant impurity of one conductivity type alloyed to a wafer of semiconductor material of the opposite conductivity type, includes the steps of forming the whisker by bending a wire of predetermined diameter to a predetermined shape, placing an end of the whisker in contact with the wafer and advancing the other end a predetermined distance towards the wafer so that the whisker presses against the wafer with a predetermined pressure, and passing an electric current between the whisker and wafer for sufficient time to alloy the whisker to the wafer and thereby to remove the pressure between the whisker and wafer by dissolution of the end of the whisker in contact with the wafer. The device, Fig. 1, comprises a base element 10, having a germanium wafer 15 soldered to a lead wire 13 fused by a glass bead 12 to a glass envelope 11, and an insert element 16 having a lead wire 17 fixed in a glass bead 18 and carrying a wire whisker 19. The whisker comprises an alloy of 98% gold and 2% arsenic. The elements are fed to a machine, Fig. 2, having pairs of holders arranged on the periphery of an intermittently rotating turret, each pair comprising a base holder 21 and an insert holder 22 adapted for vertical reciprocation along its axis towards and away from the base holder. A friction brake 23, 24 prevents unintentional movement of the insert holder. During movement of a holder pair to the first operating station the insert holder 22 is forced downwardly by cam means (not shown) to place the insert 16 within the base 10 with the whisker close to, but not touching, the germanium wafer. At the first station the insert holder is positioned under the arm 57 of a depressing mechanism comprising a constant speed synchronous electric motor 27 (Fig. 3, not shown) which drives a cam 36 through reduction gearing 28 and a one-turn clutch 33 actuated by a solenoid 35. The cam has an accurately contoured spiral surface and a short return portion so that the crank 38, which is pivoted at 39 and carries a follower roller 37, is turned at a constant rate. The crank 38 is attached by a link 42 to a second crank 47 secured to a shaft 49 which is adapted to be connected with the shaft 54 carrying the arm 57 by a magnetic clutch 53. The arrival of a holder pair at the first operating station actuates a switch which energizes the solenoid 35 and magnetic clutch 53 and thereby causes the arm 57 to start its descent. When the whisker 19 contacts the wafer 15 it completes a circuit to actuate a millisecond timer which disconnects the magnetic clutch 53 after a predetermined time interval. During this interval the insert holder 22 is being forced downwardly at a constant speed by the arm 57 so that when the clutch 53 is disconnected the resilient whisker is pressed against the wafer with an accurately predetermined force. When the cam 36 has completed its turn and the arm 57 has been re-set by a spring 59, the holder pair is indexed to a second operating station at which a predetermined current is passed through the semi-conductor device to weld the whisker to the wafer, the degree of diffusion of arsenic into the germanium being dependent on the contact pressure between the parts. The base holder 21 is provided with a heater which surrounds the glass envelope 11 and is actuated as soon as the welding is completed to seal the glass bead 18 to the envelope 11 and to anneal the glass in the device.