Microstructures and properties of Bi-10Ag high temperature solder doped with Cu element

High temperature Bi-10Ag solders with different amounts of Cu were used to investigate the impacts of Cu on the microstructures, melting characteristics, wettability and shear strength of the Bi-10Ag-xCu (x = 0, 0.5, 1, and 2 wt%) solders. A metastable Cu-rich phase was formed due to the addition of Cu. The Cu has negligible effect on the solidus but it can decrease about 6 degrees C on the liquidus. Doped with 0.5 wt% of Cu, the solders showed the largest melting range in the DSC curves and improved wettability on Cu substrates. When the Cu addition excesses to 0.5 wt%, it will induce negative effects on wettability of the solders on the substrate. Moreover, the addition of Cu has no significant influence on the strength of the Bi-10Ag lap solder joints. The Bi-10Ag-0.5Cu solder joint has higher shear strength than that of Pb-5Sn.