Effects of Bi and Ni addition on wettability and melting point of Sn-0.3Ag-0.7Cu Low-Ag Pb-free solder

Bi and Ni were added to Sn-0.3Ag-0.7Cu low-Ag solder, to fabricate new low-Ag solders, Sn-0.3Ag-0.7Cu-XBi (X= 1.0, 3.0, 4.5) and Sn-0.3Ag-0.7Cu-XNi (X=0.05, 0.10, 0.15). Melting point tests were carried out with DSC (differential scanning calorimetry) instrument. Wettability tests were conducted on a wetting balance instrument. Test results of the two new solders were compared with that of Sn-0.3Ag-0.7Cu respectively to study the effects of the adding elements on the melting point and wettability of the low-Ag Pb-free solder. It shows that Bi addition has striking positive effects on decreasing the melting point and improving wettability. Ni addition could improve the wettability as well, although not as much as Bi does. And Ni has a negative effect on melting point. With proper adding amount as X=3.0, Bi could significantly improve the wettability and decrease melting point at the same time. However, too much Bi addition could increase the melting range between liquidus and solidus, which may lead to the initiation of solidification crack of the solder joints.