Development of new Sn-Ag-Cu lead-free solders containing fourth elements

Controlling solidification behavior becomes one of the key factors because the formation of solidification defects must be prevented in order to accomplish stable and reliable assembling. It is expected that the addition of some solidification nuclei for Sn-Ag-Cu solder can refine the solidification microstructure and suppress undercooling. In this study, the effects of the fourth elements, i.e., Ni and Co, on microstructural features of Sn-3 wt%Ag-0.5 wt%Cu lead-free solder and Cu joints were investigated. The interfacial phases of Sn-3Ag-0.5Cu/Cu joints are typical Cu/sub 6/Sn/sub 5/ scallops. Sn-3Ag-0.5Cu (-0.1 wt%X; X=Ni and Co)/Cu joints form very fine Sn-Cu-Ni and Sn-Cu-Co scallops at the interface. The growth kinetics of total ternary compound layers was examined. The apparent activation energies of Sn-Cu-Ni and Sn-Cu-Co layers were 64 and 112 kJ/mol, respectively. The useful effects of preventing solidification defect and improving solder structure are obtained by the addition of Ni and Co.