Investigation into Failures of Al Wires Bonded to Au Metallization in Microsubstrates

The morphology and microstructural characteristics of Al-wire bond to Au metallization in microsubstrates was investigated by SEM, electron probe and Auger spectroscopy. It is shown that the ultrasonic bonding creates an interaction zone about 5 μm deep. Low bond strength and failure of the bond after H2 soldering cycle is attributed to impurities in the Au inks. These impurities form brittle intermetallics with Al and brittle, readily reducible, low melting glasses.