Multi-scale modeling of the viscoplastic response of As-fabricated microscale Pb-free Sn3.0Ag0.5Cu solder interconnects

A mechanistic multiscale modeling framework is proposed, to capture the dominant creep mechanisms and the influence of key microstructural features on the measured secondary creep response of microscale as-fabricated Sn3.0Ag0.5Cu (SAC305) solder interconnects. Mechanistic creep models of dislocation climb and detachment are used to capture the dispersion strengthening mechanisms in the Sn–Ag eutectic phase. These models are combined at the next length scale, with micromechanics-based homogenization schemes, to capture the load-sharing between Sn dendrites and intermetallic phases. The next higher length scale (Sn grains) is not addressed here since secondary creep response is empirically found to be insensitive to grain microstructure. Theoretical insights into the influence of microstructural features on the viscoplastic behavior of microscale SAC305 interconnects are provided. The model effectively captures the effect of alloy composition and aging loads on SAC solders, thereby aiding in the effective design and optimization of the viscoplastic behavior of SAC alloys.