Effects of rare earth element Pr and Nd on microstructure of Sn-0.3Ag-0.7Cu-0.5Ga lead-free solder

The effects of rare earth element Pr and Nd addition on the microstructure of matrix and interface of Sn-0.3Ag-0.7Cu-0.5Ga lead free solder were investigated, so was the shearing strength of the solder joints. The results show that the microstructure of the solder matrix was optimized with the addition of Pr and Nd, and the effect of Pr on the solder is better than that of Nd. The intermetallic compounds (IMC) of the solder matrix with the addition of rare earth element Pr distribute homogeneously, but it appears regional IMCs with the addition of rare earth element Nd which become the birthplace of the cracks. The absorption of rare earth elements can reduce the interface reaction between solder and Cu substrate, improve the morphology of the interface. The solder with Pr addition can combine with Cu substrate preferably so the shearing strength of the solder joints can be enhanced better.