Effect of Mn on Sn-Ag-Cu ternary lead free solder alloy-Cu assembly: a comparative study

In the present investigation, transition joints were produced by soldering Sn-Ag-Cu and Sn-Ag-Cu-Mn alloys to Cu substrate. Microstructure and mechanical properties of the assemblies were determined in reflowed condition and after aging at 100 degrees C for variable time. The shear strength as well as the reaction layer thickness of Sn-Ag-Cu versus Cu is lower in comparison to Sn-Ag-Cu-Mn versus Cu solder assembly in reflowed condition. The reaction zone for Sn-Ag-Cu versus Cu is decorated with Cu3Sn and Cu6Sn5; however, in the case of Sn-Ag-Cu-Mn versus Cu assembly only Cu6Sn5 was observed. Mn is responsible for enhanced width of Cu6Sn5, which act as a barrier layer restricting the diffusion of Sn across the interface and Cu3Sn formation has not been found even after aging of 200 h. Aging treatment leads to growth of intermetallic layer for both the joints and decrement in shear strength of the assemblies. Still Sn-Ag-Cu-Mn versus Cu solder assembly exhibits superior mechanical strength than Sn-Ag-Cu versus Cu transition joint.