Sharp Interface Simulation of IMC Growth and Void Evolution in Solder Microbumps

A reliability challenge that arises in 2.5D/3D packages is the voiding of the solder microbump accompanied by the growth of Cu-Sn IMCs in the Cu pillar under electro/thermomigration effects. A reaction-diffusion model governing the multi-physics phenomenon is needed to capture the behavior. In addition, as the size of the microbump decreases, surface diffusion effect also becomes significant. In this work, a solid-state reaction-diffusion model accounting for surface diffusion in addition to bulk diffusion is first proposed, and the governing equations are derived from first principles using continuum thermodynamics. To perform sharp interface simulation, an explicit interface tracking method termed Enriched Isogeomentric Analysis (EIGA) is used. EIGA has the advantage of exactly obtaining the geometric quantities such as the interface normal and curvature that is required to evolve the interface during analysis. However, these geometric properties can only be approximated in the limit of mesh refinement in the commonly used implicit methods such as phase-field and level-set methods. Additionally, EIGA avoids remeshing of the domain when the interface moves. Full joint simulation is carried out considering both intermetallic compound growth and void evolution in solder microbumps. Influence of electrical current stressing is also studied.