Effect of the anisotropic characteristics of beta-Sn on current-induced solder evolution

The miniaturization trend of three-dimensional integrated circuits poses great challenges to solder reliability under high current stressing since anisotropic issues tend to be enhanced in microscale solder bumps. To address these challenges, the solder evolution at the microscale and the corresponding mechanism should be addressed. In this study, by considering the anisotropy of beta-Sn in the electrical, thermal, mechanical and diffusional characteristics, the current-induced solder evolution of a typical solder bump was comprehensively explored over time. The results confirmed that the anisotropy of beta-Sn aggravated the nonuniform distribution of current-induced stresses, further causing multiple migration modes coupled in the solder bump. The spatial inconsistency between the distribution of beta-Sn unit cells and the bump geometry led to accumulation of torsion forces, which became the direct reason for solder rigid rotation. The electron-dislocation interaction promoted dislocation slip, leading to lattice rotation and homogenization of intragranular deformation. In addition, current-induced grain merging via detwinning was observed, and its velocity was faster than imagined. Our study is conducive to thoroughly understanding anisotropic evolution and establishing accurate damage mechanisms for micro solder bump design under current stressing. (C) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).