Abstract

We examined the joint strength of several Pb-free solder bumps, which are Sn-Ag-Cu alloys varied in content of Ag and/or Cu and formed on the Sn-plated Cu pad, by the bump pull test and the impact-shearing test (micro-shot test). The bump pull test showed that the Sn-3Ag-Cu bump is more brittle than the Sn-1Ag-Cu bump at the Cu-Sn intermetallic layer. The impact-shearing test(micro-shot test) showed that while the impact strength of the Sn-Ag-0.5Cu bump is superior to others, it is considerably lowered after aging at 125°C for 500 hours. The observations of the fracture surface and the cross-section revealed that the voids occurred at the interface between Cu and Cu-Sn intermetallic layer and grown up with Cu-Sn diffusion degrade the mechanical strength of the solder joints.