Effects of trace amount praseodymium and neodymium on microstructure and mechanical properties of Sn-0.3Ag-0.7Cu-0.5Ga solder.

The effects of trace mount of rare earth elements Pr and Nd addition on Sn-0.3Ag-0.7Cu-0.5Ga lead free solder were investigated by observation of microstructure and the morphology of interface layer, as well as the test of shearing strength of the solder joints. The results show that the microstructure of the solder matrix can be optimized by appropriate addition of Pr and Nd, but the scalloped and 'region-like' compounds (IMCs) appear in the solder matrix with excessive Pr and Nd addition respectively which may result in the stress concentration and become the birthplace of the cracks. The behavior of absorption of rare earth elements can retard the interface reaction between solder and Cu substrate, refine the morphology of the interface layer. The shearing strength of the solder joints can be enhanced better with appropriate addition of Pr than Nd by improvement of nucleation rate and control of growth rate of the grains near the interface layer. [ABSTRACT FROM AUTHOR]