Crystal orientation of β-Sn grain in Ni(P)/Sn-0.5Cu/Cu and Ni(P)/Sn-1.8Ag/Cu joints

Electron backscatter diffraction analysis was used to compare the crystal orientation of β-Sn grains in Ni(P)/Sn-0.5Cu/Cu and Ni(P)/Sn-1.8Ag/Cu joints before and after aging. In Ni(P)/solder/Cu joints, the solder composition (Cu versus Ag) significantly affects β-Sn grain orientation. In Ni(P)/Sn-0.5Cu/Cu, there are two types of small columnar grains grown from Ni(P) and Cu under bump metallurgy with a high-angle grain boundary crossing the joint closer to the Ni side; in contrast, Ni(P)/Sn-1.8Ag/Cu has large grains with low-angle boundaries. During thermal aging at 150 °C for 250 h, the Ni(P)/Sn-0.5Cu/Cu joints undergo a more significant microstructural change than the Ni(P)/Sn-1.8Ag/Cu joint. Additionally, obvious ledges developed along the high-angle grain boundary between the upper and lower areas in the Sn-0.5Cu joint.