Microstructure-based fatigue analysis of SiC power module with sintered silver die attach

Sintered silver offers excellent performance for die attach materials in power modules, but internal defects such as pores in sintered silver can deteriorate the mechanical behavior and overall lifetime of power modules. This work establishes a porous microstructure model of die attach sintered silver by combining the Gaussian filter technique with macro finite element analysis. The model provides topology information for the assignment of material properties to sintered silver and enables the investigation of the porous microstructure effect. The thermo-mechanical behavior and fatigue lifetime of the power modules with different thicknesses of sintered silver die attach layers under power cycling are examined. Results show that the simulated porous microstructure of sintered silver is in good agreement with the experiment; the stress and viscoplastic dissipation energy density are higher for the power modules with thinner sintered silver die attach layer, and there is a significant stress concentration near the interface between the chip and sintered silver. Increasing sintered silver layer thickness reduces accumulated viscoplastic strain and improves the fatigue lifetime of the SiC power module, and the simulation results are consistent with the experimental observation. Furthermore, the pores significantly reduce the fatigue lifetimes of the power modules. The findings of this work would provide valuable insights for thermo-mechanical analysis and fatigue lifetime prediction of SiC power modules considering porous microstructures of sintered silver.