Influence of Phase Coarsening on Inhomogeneous Deformation and Fracture Behavior in Sn–Bi Solder Interconnects

With the increasing demand for emerging technologies like artificial intelligence and big data, the significance of advanced chip integration and packaging has grown considerably. Sn-Bi based solders have gained significant attention and have been explored for multi-layer stacked packaging, but they are prone to significant coarsening during service, and the effects of grain and phase anisotropy become more pronounced. These factors impact the performance and reliability of Sn-Bi solder interconnects. This study develops a numerical model to investigate microstructure coarsening in Sn-Bi solder bump interconnects, focusing on its effect on mechanical behavior and crack propagation. The simulated coarsening behavior aligns with experimental observations. Results show that, under shear loading, the Sn-rich phase experiences higher stress initially, while the Bi-rich phase bears greater stress later, leading to stress concentrations mainly in the Bi-rich phase or at the phase interfaces. Thermal aging exacerbates the uneven distribution of stress. Plastic strain is greater in the Sn-rich phase, and cracks primarily initiate and propagate in the Bi-rich phase. Coarsening accelerates crack growth, affecting the stress-strain response. This study provides insights into the effects of phase coarsening and inhomogeneous deformation in Sn-Bi solder interconnects, which may contribute to interconnect design and reliability analysis in three-dimensional packaging.