Solder die attach lifetime characterization of SOT-227 power MOSFET module in a three-phase inverter under power cycling

This study aims to assess the power cycling lifetime of the solder die attach of the silicon (Si) power metal-oxide-semiconductor field-effect transistor (MOSFET) modules in an SOT-227 package in a three-phase bridge inverter. This goal is achieved through a loose one-way coupling framework that incorporates a thermal computational fluid dynamics (CFD) model for temperature estimation and a transient thermal-mechanical finite element model (FEM) that accounts for the time-dependent viscoplastic behavior of the solder die attach through the Anand viscoplastic constitutive model for thermal-mechanical responses assessment. To facilitate an accurate prediction of the solder die attach lifetime during power cycling, a physical lifetime prediction model is constructed through the strain-based Coffin-Manson Eq. together with the experimental lifetime data and the corresponding calculated equivalent viscoplastic strain increments. Furthermore, parametric study via the coupling framework is conducted to examine the effect of cooling, operating and structural parameters on the solder die attach lifetime, and also to identify the most crucial design parameters. At last, experimental design using a Taguchi method is conducted to seek the optimal level combination of design parameters for enhanced power cycling lifetime of the solder die attach.