Interaction effects between the preferred growth of β-Sn grains and thermo-mechanical response in microbump interconnects under thermal cycling

Abstract

orientations of β-Sn grains have a big influence on the thermo-mechanical behavior of the microbump interconnect due to the obvious anisotropic features of thermal expansion coefficient (CTE) and elastic stiffness of β-Sn, especially with the dramatic decrease in the feature size of 3D ICs in electronics. Simultaneously, the elastic energy, induced by the deformation of grains with different orientations, can affect the grain morphology evolution during thermal cycling. Thus, some new concerns of reliability of the microbump interconnect are emerging due to the anisotropic behavior. In this study, dynamic evolution of grain morphology of the Cu/Sn/Cu microbump interconnect during thermal cycling is simulated using the phase field model, which incorporates the effects of temperature and elastic deformation energy in the grains induced by the thermal stress. The influence of the elastic and CTE anisotropy of β-Sn on the thermo-mechanical behavior of microbump interconnects with different grain morphologies is investigated, and the interaction effects of grain morphology evolution and thermo-mechanical behavior in the microbump interconnect are studied, with focus on the variations of the average diameter and average von Mises stress of β-Sn grains with different orientations in the solder of the microbump interconnect.