Influence of phase inhomogeneity on the mechanical behavior of microscale Cu/Sn–58Bi/Cu solder joints

Electronics are becoming smaller and more versatile, and the size of solder joints has decreased to tens of microns, inducing obvious inhomogeneity among the phases in the solder matrix microstructure. In this study, the influence of phase inhomogeneity on the mechanical behavior of microscale Cu/Sn–58Bi/Cu solder joints was studied. Sn and Bi single-phase solid solution samples with the same composition as the Sn and Bi phases in the Sn58Bi microstructure were prepared, and their mechanical performances, elastic constants, and power-law constitutive models were measured, calculated, and identified. Based on the obtained mechanical performances, elastic constants, and power-law constitutive models, a three-dimensional finite element model of line-type Cu/Sn58Bi/Cu microscale solder joints, including their microstructure, was established. The results demonstrate that phase inhomogeneity increases the maximum value of von Mises stress, leading to stress concentration. When the Sn58Bi solder matrix transfers from the elastic deformation stage to the plastic deformation stage, the high σ_eq zone of the matrix gradually shifts from the Sn phase to the Bi phase. In addition, a study of the anisotropy reveals that the elastic anisotropic mechanical properties of Sn58Bi solder matrix are mainly affected by the anisotropic effect of Sn. The stress concentration is the lowest when the crystal orientation is π/2.