Effect of Ni addition on the Sn-0.3Ag-0.7Cu solder joints

It is gradually recognized that Sn-Ag-Cu is better alloy system for application prospect in the lead-free solders. In order to cut down the cost and improve properties, researchers have always been searching for proper compositions and adding elements to improve properties actively. This paper has investigated the effect of Ni addition on Sn-0.3Ag-0.7Cu (SAC0307) low-Ag solder joint. The results of EDS analysis showed that the major IMC formed between the SAC0307 solders and Cu substrate was Cu₆Sn₅, while for solders with Ni addition the main IMC was (Ni_xCu_1-x)₆Sn₅. After aging, in the case of 0.05% Ni addition, the thickness of IMC layer was the thinnest regardless of aging time. SAC0307-0.05Ni solder is effective to reduce the formation of IMC at the interface during the reflow process and to inhibit the growth of IMC after aging. Additionally, the atom ratio of Ni to Cu in the (Ni_xCu_1-x)₆Sn₅ phase after reflow and after aging were also studied. Some findings of this study can be rationalized by the Cu-Ni-Sn isotherm.