Failure Prediction and Analysis of an IGBT Module for Industrial Applications Subjected to Passive and Power Cycling

The thermo-mechanical reliability of an industrial power module containing IGBTs with soldered die and module attachment and aluminum bonding wires has been investigated. In this kind of power packaging, die attachment, module attachment, and bonding wires attachment can be critical failure modes. It was one aim of the investigation to analyze these failures when the modules are subjected to different kinds of passive and power cycling. Furthermore, prediction of these failures based on finite element (FE) studies are addressed. Coupled (FE-) analyses are reported to understand the thermo-mechanical stresses in the assembly. Verification of evaluation methodologies to predict cyclic damage are in the focus of the paper. Physics-of-failure (PoF) based lifetime prediction is applied for a power stack die attach with soft solder between chip and substrate and between substrate and base-plate. An easy-to-use Coffin-Manson type failure criterion is given based on averaged cyclic creep strain and dissipation density. At the wire bonding interfaces bi-material notch effects cause stronger interface stress singularity, and therefore, damage mechanics criteria already proposed in [1] are updated and applied. Cyclic damage is calculated by the Cohesive Zone Method (CZM) and critical cycle numbers are estimated from that by a modified Paris law. The predictive laws for both thin solder layers and heavy Al bonds are compared to testing results and shown to agree well.