An EBSD Study of Fatigue Crack Propagation in Bonded Aluminum Wires Cycled from 55°C to 85°C

The texture and microstructure evolution of aluminum (Al) wire bonds of power semiconductor devices during power cycling tests were investigated using electron backscatter diffraction (EBSD). Power cycling tests in pulse width modulation (PWM) mode were performed on power modules during which the cycled devices were extracted from the test bench at different stages of the aging for analysis. The results improve our understanding of microstructural transition after wire bonding and during power cycling. After the wire was subjected to an ultrasonic bonding process, the evolution of a distinct brass textured area within the bonded interface was observed by EBSD analysis. The brass texture is discussed as a result of plastic deformation. During power cycling, grain coarsening as well as local low angle boundary conversion to high angle boundary occurs and the wire–metallization interface texture changes to an overall random orientation. Effects of microstructure and texture on the crack initiation and propagation are discussed.