2004 Volume 45 Issue 3 Pages 681-688
Thermal fatigue properties of Sn-1.2Ag-0.5Cu-xNi (x: 0.02, 0.05, 0.10 and 0.20 mass%) flip chip interconnects was investigated to find out an ideal nickel composition. Sn-1.2Ag-0.5Cu-xNi (x: 0.05, 0.10 and 0.20) had longer thermal fatigue life than Sn-1.2Ag-0.5Cu-0.02Ni. Cracks developed near solder/chip interface for all the bumps tested, and fracture due to thermal strain was a mixed mode, both transgranular and intergranular. Sn grain growth after thermal cycling was suppressed for Sn-1.2Ag-0.5Cu-xNi (x: 0.05, 0.10 and 0.20) solder joints, while Sn grains grew faster for x = 0.02, which suggests that suppression of Sn grain growth enhanced thermal fatigue endurance. Therefore, thermal fatigue properties of Sn-1.2Ag-0.5Cu-xNi (x: 0.02, 0.05, 0.10 and 0.20) solder joint correlated to its microstructure, and the addition of 0.05 mass%Ni is required to enhance thermal fatigue endurance.