Thermo-mechanical simulation of plastic deformation during temperature cycling of bond wires for power electronic modules

Modelling was undertaken to investigate the role of bond wire size on reliability in power electronic converters. Experiments have shown that thin 125 µm Al wires used in place of 375 µm Al wires alleviate bond wire lift-off and further outlast other sources of failure such as solder degradation in a power module. To investigate the role of bond-wire size on wire lift-off, the effective plastic strain was estimated through thermo-mechanical simulation. Three-dimensional models were constructed for the thin and thick bond wires, respectively. For the critical deformation of the aluminium bond wires during thermal cycling, a temperature-dependent bi-linear plasticity model was used. The effect of a difference in yield strength for the thin wires was also investigated. Maximum as well as volumetrically averaged values of the effective plastic strain showed significant differences between the thick and thin wires and wires with different yield strengths. The modelling results show higher effective plastic strain for the thick wires - supporting the experimental findings.