Deformation behavior of sintered Ag in relation to densification during spherical indentation creep test

Although sintered Ag is a promising die-attach material for high-temperature wide-bandgap power modules, its porous microstructure promotes creep deformation and joint degradation. Nanoindentation has been widely used to evaluate the local mechanical and creep properties; however, in porous sintered Ag, creep response is strongly affected by indentation-induced densification. In this study, the effect of densification on creep behavior was examined by performing spherical indentation creep tests combined with three-dimensional focused ion beam–scanning electron microscopy reconstruction, electron backscatter diffraction, and finite element simulations based on the 3D microstructure. The spherical indentation creep tests revealed a nonstandard equivalent creep stress exponent, suggesting an apparent power-law breakdown. The apparent power-law breakdown can be attributed to the high stress beneath the indenter and the concentrated stress at the necks and within the locally densified regions. These findings suggest that indentation-induced densification affects the apparent creep response of sintered Ag and must be considered when evaluating creep deformation behavior.