Joint Strength between Sn-Ag Based Lead-free Solder and Cu Pad by Ball Shear Test

The interfacial reaction between the solder/Cu plate and the joint strength of the solder joint with a Cu pad were investigated for both as-reflow and thermal exposed conditions in this study. Sn-3.5mass%Ag-xCo solders (x=0, 0.1, 0.5, 1.0 mass%) were specially prepared. A reaction test between solder and a Cu plate was performed to reveal the effect of the addition of Co to solder on the morphology of intermetallic compounds at the interface. A bump shear test of the solder joint on a Cu pad was carried out to evaluate the effect of the addition of Co to solder on the joint strength of the solder with a Cu pad. As a result of the reaction test, it was clear that the formation of an intermetallic compound (IMC) layer at the interface for Sn-3.5Ag-Co solders was quite different from that for binary Sn-3.5Ag solder. During the aging process at 423K, the growth rate of the IMC layer for Sn-3.5Ag-Co solders was slow compared to that for binary Sn-3.5Ag solder. As a result of the bump shear test, it was clear that there was little difference in the shear strength between a Sn-3.5Ag solder joint and Sn-3.5Ag-Co solder joints, though the IMC morphology at the interface was quite different.