Interfacial properties of Zn-Sn alloys as high temperature lead-free solder on Cu substrate

The potentials of the newly designed Zn-xSn (x = 40, 30. and 20 mass%o) alloys as high temperature lead-free solders and their interface properties on Cu substrate were investigated, focusing oil the interface microstructure and mechanical properties. Hypereutecic alloys show two endothermic peaks in differential scanning calorimetry (DSC), one appears at 200 degrees C and the other varies froth 365 to 383 degrees C with decreasing SO content. These peaks are well associated with the eutectic and liquidus temperatures of binary Zn-Sn alloys, and little undercooling were observed oil cooling. Two Cu-Zn compound layers are formed at the Zn-Sn alloys/Cu interface. The reaction phases are identified as gamma-Cu5Zn8 and epsilon-CuZn5 phases from the Cu side, and no Cu-Sn compound was identified. The thickness of the reaction layers and the joining strength increased with decreasing SO content. Each joint shows a different fracture pattern, which gradually changes from transgranular in Zn-Sn alloys near the interface to the at epsilon-CuZn5/gamma-Cu5Zn8 reaction layers with decreasing Sit content.