Microstructural Analysis of the Bonding Interface between Thick Al Wire and Al-1 mass%Si Electrode Film

Enhancing reliability of thick Al wire bonds in high power transistor modules is very important. In order to estimate bond reliability, microstructural analyses of the bonding interface between Al wires and Al–Si electrode films have been investigated. The bonding interface between Al wire and Al–Si electrode film were composed of three kinds of microstructures, i.e. coincidence boundaries, layers of very fine grain size, and layers with very high dislocation density. These boundaries were assumed to be very strong and hence very stable in the reliability tests. After power cycle tests, the fine grain layers and the layers with a very high dislocation density disappeared almost completely and form a good quality bonding interface. Very thin amorphous layers 10–200 nm thick were found to be produced partly at the interface. This may be formed through a process in which amorphous phases in the very fine grain size layer were pushed out to the interface by grain growth during the power cycle tests.