Effect of Bi Addition on Tensile Properties of Sn-Ag-Cu Solder at Low Temperature

In order to examine the effect of the Bi addition on tensile properties of Sn-Ag-Cu solder at low temperatures, stress-strain diagrams were acquired by tensile tests at 233K using miniature size specimens. Stress drops were observed in the stress-strain diagram of Sn-Ag-Cu-Bi solder before it lead to a break. Similar phenomenon did not observed in the Sn-Ag-Cu solder. The stress drops was exceptionally sharp in the Sn-Ag-Cu solder with added 3 mass% Bi, compared to the solder with added 1 or 2 mass% Bi. The mode of the stress drop is depended on twin deformation. On the contrary, similar stress drop phenomenon was not observed in any stress-strain diagrams at 298 K. From the results of grain map analysis, it was found that many twin deformations occur in the specimen in which exceptional sharp stress drops appear in the stress-strain diagram.