Effects of bonding conditions and surface state on bondability: Study of Cu wire stitch bonding (1st Report)

Summary

In mass production of semiconductors, wire bonding is used to make electrical connections between an electrode terminal on a semiconductor chip and an outer lead terminal. Cu wire offers good corrosion resistance and high electrical and thermal conductivity. Cu wire can also be directly bonded to Cu alloy lead frames by stitch bonding. For this reason, practical application of the Cu wire bonding process is anticipated. Cu wire stitch bonding on Cu alloy lead frames, however, faces numerous difficult problems.

This paper describes an investigation of the effects of the bonding conditions and surface states on bondability during Cu wire stitch bonding. It is necessary to exercise good control of the wire deformation behaviour to obtain good bondability in thermosonic Cu wire bonding (hot‐pressure bonding combined with ultrasonic vibration). The surface state of the Cu alloy lead also affects the bondability. If the surface roughness of the Cu alloy lead is more than 0.4 μm or if the thickness of the oxide film on the Cu alloy lead is more than 10 nm, inferior bondability during Cu wire stitch bonding is obtained.