The mechanical and physical properties of the phases in the microstructure of Sn- Bi solder alloy

In this study, Sn58Bi solder alloy and solid solution samples of Sn-rich phase and Bi-rich phase were prepared, and their mechanical and physical properties were tested. The elastic moduli of Sn58Bi, Sn-rich phase and Bi-rich phase are 42.30 GPa, 61.10 GPa, and 31.90 GPa, respectively, and their hardnesses are 0.33 GPa, 0.37 GPa, and 0.28 GPa, respectively. The resistivity of Bi-rich phase is much higher than that of Sn-rich phase. As the test temperature was increased from 300 K to 400 K, the resistivity of Bi-rich phase increases slightly, while that of Sn-rich phase is almost unchanged. Different with the resistivity, the specific heat capacity of Sn-rich phase increases slightly with the increase of temperature, while the specific heat capacity of Bi-rich phase is quite stable. The thermal conductivity of Sn-rich phase is much higher than that of Bi-rich phase, indicating that the Sn-rich phase in the eutectic structure has better heat dissipation performance. Meanwhile, the coefficient of thermal expansion (CTE) of Sn-rich phase is larger than that of Bi-rich phase.