Patent GB-1153002-A (GB)
Title: Vibratory Bonding methods and apparatus
Inventor: CHRISTENSEN FRANK WAMBOLDT
IPC: B23K20/10
Filed: 1966-06-16
Abstract: 1,153,002. Welding by pressure. WESTERN ELECTRIC CO. Inc. 16 June, 1966 [19 July, 1965], No. 26951/66. Heading B3R. [Also in Division H4] In joining two members by applying a pulse of vibratory energy to the members by a bonding head energized by an energy pulse of predetermined duration, the members are held in contact and the vibrations of the bonding head are damped after cessation of the energy pulse. An apparatus for bonding a fine wire e.g. of silicon-aluminium to a transistor stripe e.g. of gold with an optimum bond i.e. where the peel strength at least equals the tensile strength, comprises a sonotrode including a velocity transformer 21, Fig. 5, a tapered portion 22 carrying at one end a bonding tip 25 and a magnetostrictive transducer 23. A stub shaft 27 extending from the transformer 21 into a slot 29 in the portion 22 carries a disc shaped resonant damper 31 of lead, brass, plastic &c., which vibrates in dissonance with the sonotrode. The damper is positioned on an antinodal plane to absorb maximum energy and its edge is one quarter of a cycle out of phase with the rest of the apparatus. The bonding tip comprises a pair of parallel cylindrical members 36 forming a groove 38 to receive the wire. The magnetostrictive transducer may be replaced by piezo-electric, e.g. quartz crystals, or electrostrictive e.g. barium titanate transducers. In one modification, a pair of spaced dampers are mounted on the stub shaft and in another a large damper disc 62, Fig. 14, is mounted at the end of the velocity transformer 63 to form a step, the transformer is provided with circular grooves 68 which form a damper 69 between them and a narrow horn 66 carrying the bonding tip 67 has circular grooves 71 which form dampers 72 therebetween. A power supply to provide bonding pulses as short as 10 microseconds comprises a supply connected to an oscillator and electronic switch, an amplitude control and a power amplifier. The oscillator generates an oscillatory input signal having a frequency compatible with the resonant characteristics of the bonding apparatus and a portion of the signal is selected by the electronic switch to provide a short pulse oscillatory input signal which is stabilized by the amplitude control to provide a signal which is amplified to provide a short pulse bonding signal. Instead of the disc dampers described an eddy current brake in the form of a ferromagnetic member mounted on the bonding apparatus for movement perpendicular to the lines of flux of a magnet or an electrical circuit wherein a negative feedback loop is provided for feeding the signal generated by the vibrations of the transducer, which continue after the cessation of the short pulse signal, to the amplifier where they are fed back to the transducer out of phase may be used. It is stated that below a certain minimum pulse time and above a certain maximum pulse time optimum bonding is not obtained even though clamping pressure and applied power are increased. In examples where the minimum time is 450 microseconds a gold wire 291, Fig. 21, of a transistor is bonded to the gold plated iron-nickel-cobalt alloy header 294 with a clamping force of 18-24 grams and a pulse time of 650 microseconds at 60 KC per see., the gold wire 291 is bonded to a gold plated iron-nickel-cobalt post 296 with a clamping force of 21-34 grams and a pulse time of 650 microseconds at 60 KC per sec., and a gold wire 299 is bonded to a vapour plated aluminium stripe 297 on a silicon wafer 293 with a clamping force of 30-39 grams.