Fatigue life enhancement of low silver content Sn-Ag-Cu flip-chip interconnects by Ni addition

The mechanical shear fatigue test has been performed to investigate the fatigue properties of Sn-1.2 mass%Ag-0.5 mass%Cu-0.05 mass%Ni for flip chip interconnections. The low cycle fatigue endurance of the alloy is almost equivalent to that of Sn-3 mass%Ag-0.5 mass%Cu alloy, even though the fatigue endurance of Sn-1 mass%Ag-0.5 mass%Cu alloy was poorer than that of the 3 mass%Ag alloy. Adding Ni to low silver content Sn-Ag-Cu alloy leaded to fine microstructure, and the microstructure had a network structure of Ag3Sn intermetallic compound together with fine Cu-Sn intermetallic compound. The microstructure resulted in high strain hardening exponents, which leaded to good low cycle fatigue endurance of the alloy.