Comparison of Interfacial Stability of Pb-Free Solders (Sn—3.5Ag, Sn—3.5Ag—0.7Cu, and Sn—0.7Cu) on ENIG-Plated Cu During Aging

The solid-state interfacial reactions of Pb-free solders (Sn-3.5Ag, Sn-3.5Ag-0.7Cu, and Sn-0.7Cu) with electroless nickel-immersion gold (ENIG)-plated Cu substrate, and the growth of interfacial intermetallic compound (IMC) layers were investigated and compared during aging at 200^??C for up to 1000 h. The Sn-3.5Ag-0.7Cu solder exhibited a higher IMC growth rate and a higher consumption rate of the Ni(P) layer than the other two Pb-free solders. The interfacial reaction of the Sn-0.7Cu/ENIG-plated Cu system during aging was the slowest among the three kinds of solder joint. The thickness of the interfacial IMCs were ranked in the order Sn-3.5Ag-0.7Cu > Sn-3.5Ag > Sn-0.7Cu. The higher melting temperature of the Sn-0.7Cu solder and the presence of Cu element within the solder suppressed the growth of the interfacial IMC layer and the consumption of the Ni(P) layer, resulting in the superior interfacial stability of the solder joint at high temperature of 200??C.