Microstructures and solderability of SnCuNi-xPr lead-free solder

Effects of rare earth element Pr on the wetting performance,mechanical properties and microstructures of Sn0.7Cu0.05Ni lead-free solder were studied.The inherent relationship between the microstructures and properties of the solder was preliminarily discussed.The experimental results show that the suitable amount of Pr addition is 0.025%-0.075%,and the most appropriate amount is 0.05%,at which composition the solder exhibits the best wetting performance and mechanical properties.The surface tension of the liquid solder was significantly reduced due to the addition of rare earth Pr and the wetting performance was improved.The microstructures of the soldered joints were evidently refined,which resulted from the pinning effect on the grain boundaries migration due to the addition Pr,and the shear strength was improved obviously.It was also found that the activity of the rare earth element of Pr may be reduced because of excessive oxidation and the enlargement of the comprehensive effect of stress field caused by excessive addition of Pr.