Effect of Ni on the morphology of IMC and mechanical properties of SAC-Bi-Ni/Cu joints

The effects of Ni element on the morphology of intermetallic compounds and some mechanical properties of SAC-Bi-XNi/Cu lead-free solder joints have been investigated. The corresponding mechanical and reliability behaviors were evaluated by performing shear test, fracture mode analysis, nanoindentation experiments and measurement of IMC before and after isothermal aging 200h and 400h at 160°C. The results indicated that with increasing the content of Ni (0~0.15 wt %), hardness of solder increased, shear strength of solder joints and modulus of elasticity of solder increased and then decreased. SAC-Bi-0.1Ni lead-free solder showed the largest shear strength and Young´s modulus. The fracture dimples in SAC-Bi-0.1Ni solder joints were less than other three solders. The thickness of IMC increased originally and then decreased after reflowing, which was thinnest in SAC-Bi-0.05Ni/Cu solder joint. Ni apparently refined the grains of IMC.