INFLUENCE OF AL FILM THICKNESS ON BONDABILITY OF AU WIRE TO AL PAD

In the Au wire bond to Al pad on a monolithic IC, it is found that the bond degradation due to heat treatment after thermosonic ball bonding depends on the thickness of the Al film on the SiO2/Si substrates. The bond degradation is lessened with thinning Al film. In the specimens with 0.2 mum and 0.5 mum Al films, the change in the bond resistance is small and the shear strength is almost invariable. In this case, the bond degradation is improved by reason of the fact that the volume of the diffused layer is reduced. It is also shown that the adhesion of the diffused layer to Au and SiO2 is very strong and a little Kirkendall void is detected. In the specimens with Al films thicker than 0.5 mum, the bond resistance much increases and the bond shear strength decreases.