Paris Law Applied to Wire Bonds Degradation Using Crack Growth Measurement

Abstract:
Power Modules (PMs) with a standard packaging technology reveal weaknesses after long operation time due to thermomechanical fatigue. Top electrical interconnections, or wire bonds, used in PMs are the most critical components prone to degradation leading to the device failure. In this paper, a crack growth lifetime model dedicated to wire bonds fatigue is constructed to estimate the PM lifetime under Power Cycling Tests (PCTs) conditions. The proposed model considers lifetime dependence on junction temperature extent (DeltaTj) and heating time (ton) as main load parameters. The PCTs are conducted under high switching frequency and high DC bus voltage conditions. The tested PM integrates a singlewired chip instrumented with auxiliary sensors to estimate the crack growth rate in-situ during the PCTs. In parallel, a nonlinear fracture parameter is evaluated using an electro-thermo-mechanical Finite Element Model (FEM). Combination of crack length measurement and the selected crack-tip parameter allows to confirm the Paris law and finally to build the fracture-mechanics lifetime model.