Effect of minor addition of Pb upon interfacial reactions and mechanical properties at Sn-3.0Ag-0.5Cu/Cu and Sn-58Bi/Cu solder joints

Abstract Interfacial reactions and mechanical properties between the Cu and Pb-free solders, Sn-3.0Ag-0.5Cu and Sn-58Bi with addition of 0.1 to 1.0 wt.% Pb are investigated in this study. Two kinds of intermetallic compounds, scallop-shaped Cu6Sn5 and plane layered Cu3Sn phases, were found in both Sn-3.0Ag-0.5Cu + Pb/Cu and Sn-58Bi + Pb/Cu couples. The intermetallic compound thickness increased with longer reaction times, higher reaction temperatures and greater Pb contents. The Cu6Sn5 phase was the thicker intermetallic compound in the Sn-3.0Ag-0.5Cu + Pb/Cu couple. However, in the Sn-58Bi + Pb/Cu system, the Cu3Sn phase is the thicker intermetallic compound. Experimental results indicate that the higher Pb concentration in Sn-3.0Ag-0.5Cu or Sn-58Bi solders reduces the alloy liquidus temperature and increases the thickness of the intermetallic compound. Thicker intermetallic compounds reduce the mechanical strength of the solder joint.