Generic Lifetime Model for Wire Bonds Degradation in IGBT Modules Based on a Fracture Mechanics Parameter

Inhalt:
Junction temperature variation (DeltaTj), minimum junction temperature (Tjmin) and heating time (ton) are pointed out as the most influencing load parameters limiting the lifetime of standard power modules (PMs). In this work, a large series of DC power cycling tests (PCTs) are conducted on IGBT PMs targeting a considerable range of variation for each load parameter. The tested PMs are based on heavy aluminum wires (400 um diameter) used as top electrical interconnections. Post-analysis of tested devices and acquired measurements during the PCTs revealed wire bond lift-off as the predominant observed failure mechanism. A generic Physics-of-Failure (PoF) model is proposed to establish different trends and dependencies according to each parameter DeltaTj, Tjmin and ton. It relies on nonlinear fracture mechanics, and more precisely a crack growth model describing crack propagation at the wire/metallization interface.