Modeling Microstructure Effects on Electromigration in Lead-free Solder Joints

This paper studies the microstructure effects on electromigration in lead-free solder joints in wafer level chip scale package (WL-CSP). It is an extension of an earlier isotropic model [1]. The three dimensional finite element model for solder joints is developed and analyzed in ANSYS (R). A sub-modeling technique combined with an indirect coupled electrical-thermal-mechanical analysis is utilized to obtain more accurate simulation results in solder bumps.. Four representative microstructures of the solder bumps are modeled and anisotropic elastic, thermal and diffusion property data are used. The results obtained from the fourrepresentative microstructures are compared with each other. The microstructure effects on electromigration are drawn from the plots of the atomic flux divergence (AFD) and the time to failure (TTF) with respect to microstructure parameters.