Effects of Ni addition on microstructure and the shear strength of Sn-3.0Ag-0.5Cu/Cu solders joints

The effects of the fourth Ni element on microstructure and monotonic shear strength of Sn-3.0Ag-0.5Cu lead-free solder were investigated. The addition of the Ni element makes the new (Cu_xNi_1-x)₆Sn₅ phase, which improves the solder microstructure. The results indicate that the addition of Ni element increases the shear strength of solder joint. When the content of Ni is 0.10 wt.%, the shear strength of solder joint is the highest by 40.28 MPa which is 18% higher than that of Sn-3.0Ag-0.5Cu lead-free solder. The fracture morphology shows that the addition of Ni promotes grain refinement which leads to the increase of shear strength. The shear strength of the solder joints decrease continuously. The fracture microstructure became coarse-rained with the increase of thermal aging time. Dimples and voids appears in the solder joints which lead to the decrease of the shear strength.