Patent GB-1255832-A (GB)
Title: Improvements relating to the manufacture of supports for semiconductor devices
Inventor: JACKSON SYDNEY
IPC: H01L21/48
Filed: 1969-04-26
Abstract: 1,255,832. Welding by pressure. FERRANTI Ltd. 16 April, 1970 [26 April, 1969], No. 21401/69. Heading B3R. [Also in Division H1] In a method of manufacturing a support for a semi-conductor device a spherical particle of a material which may be bonded to the support and to which the device may subsequently be bonded, is selected from a supply of such particles, transported to the desired area of the support and bonded thereto by an impacting tool. The particles may be of gold and bonded by thermocompression to an electrolytically deposited silver coating on a nickel-iron-cobalt alloy lead frame. Alternatively the particles may be of silver, aluminium, or copper and bonded to coatings of these metals or of gold on the support member. To protect the silver coating from oxidation a gold flash of only molecular thickness may be deposited on the silver and thermo-compression bonding carried out in an atmosphere of nitrogen. The selection and carrying of the spherical particle is preferably effected by means of a suction nozzle 17 which is adapted to enter a receptacle 11 in which the supply of particles 10 is held. The nozzle 17 is heated, e.g. to 300‹ C. and impacting of the particle on to the support is effected initially by the nozzle and subsequently by a heated impacting tool 20, e.g. of tungsten carbide having a highly polished plane end surface 21. Apparatus for simultaneously bonding gold particles to a batch of sixteen lead frames 18 mounted on an elongated strip 23 comprises a carrier 27 reciprocable laterally by cylinder and piston means 28 beneath a vertically reciprocable head 31 supporting a series of impacting tools 20 and suction nozzles 13 the carrier 27 having an undercut mounting channel 26 in and along which the strip 23 may be indexed and a series of bins 11 for the spherical gold particles. A supply of nitrogen to the bins 11 serves to agitate the particles and prevents their becoming jammed. Semi-conductor devices, e.g. transistors 25, may subsequently be bonded to the coated support areas by conventional alloying techniques to provide, e.g. a gold-silicon eutectic bond layer, and gold wire electrical interconnections 39 bonded to contacts on the upper face of the transistor and to the conductors 24 of the lead frame by thermocompression. The transistors are subsequently encapsulated in epoxy resin and the lead frames 18 separated from the strip 23 leaving conductors 24 extending from each epoxy-encapsulated device. Where the semi-conductor device is larger, e.g. in the case of an integrated circuit a plurality of gold particles may be simultaneously bonded to the support adjacent each other to form a single bonding area of larger size (Figs. 6, 7, not shown). In a modification of the thermocompression bonding process the spherical particle is laid on an anvil by the nozzle, and flattened thereon by a heated impacting tool to which the flattened particle preferentially adheres before being carried to the support member and bonded thereto by the tool (Figs. 8a to 8c, not shown).