Influence of thermal cycling on shear strength of Cu-Sn3.5AgIn-Cu joints with various content of indium

This work presents an investigation on the influence of thermal cycling of Cu-Sn3.5AgIn-Cu joints for various content of indium. Solders Sn-3.5Ag containing 0, 6.5 and 9 mass% In were prepared by rapid quenching of appropriate alloys. Joints Cu-solder-Cu were prepared in furnace at 280 °C and 1800 s. Thermal cycling was in the interval room temperature (RT)-150 °C up to 1000 cycles and in the interval RT-180 °C for 500 cycles. The shear strength of the joints with indium-free solder decreases with increasing number of cycles. On the contrary shear strength of joints with indium containing solders increases with increasing number of cycles. It is related with the thickness of Cu6Sn5 phase which makes the interface between Cu substrate and solder. In the first case the thickness of this phase is growing with increasing number of cycles, in the second case the amount of this phase is reducing with increasing the number of cycles due to the support of dissolution of copper from Cu6Sn5 phase into the Sn-Ag-In solder by indium. X-ray diffraction analysis of original solders as well as of uncycled and 1000 times cycled joints made with all three kinds of solders is given.