Tensile testing and microstructure analysis on Sn-Pb-Cd and Sn-Pb eutectic solder

Since the 50Sn32Pb18Cd eutectic solder was melted at 145 °C which is lower than the melting point of 63Sn37Pb solder (183 °C), it was selected as the interconnection joint to create a temperature gradient to avoid the former nearby 63Sn37Pb joint re-melted during the components assembly process. The tensile testing and the microstructure analysis were carried out on 50Sn32Pb18Cd eutectic solder to get the fundamental data support for the reliable applications and also on 63Sn37Pb solder for comparison. The tensile test was performed by Instron 5569 and Instron 5500R mechanical machine under different temperatures with different strain rates. The microstructure observation was conducted with SEM and EDX analysis. Results show that the tensile strength of Sn-Pb-Cd solder was much higher than that of Sn-Pb solder under the high strain rate (10^-3s^-1) at room temperature. But the value was decreased and lower than that of Sn-Pb solder when the temperature was increased to 85 °C, or the strain rate was lowered to (10^-5s^-1) at the room temperature. The yield strength of both solder materials dropped when the tensile temperature was increased or the strain rate was lowered, and the yield strength of Sn-Pb-Cd solder would decrease more than that of Sn-Pb solder. Both solder materials have uniform phase distribution but having significant different microstructure morphologies. In Sn-Pb solder, the Pb-rich phases distribute as islands in Sn-rich phase matrix. While in Sn-Pb-Cd solder, Pb-rich phases with many different shapes appear in Sn-rich matrix and Cd-rich phases mainly distribute in the form of stripes inside Pb-rich phase. The preliminary microstructure analysis of these two different solder materials indicates that the different mechanical properties is resulted from their different microstructures.