Analysis on interfacial reactions between Sn-Zn solders and the Au/Ni electrolytic-plated Cu pad

Abstract Interface reactions between Sn–Zn lead-free solders and the Au/Ni electrolytic-plated Cu pad after isothermal aging were investigated. The intermetallic compounds at the interface between solder and the Au/Ni electrolytic-plated Cu pad were examined by field-emission scanning electron microscopy and transmission electron microscopy. During the reflow, Zn firstly reacted with Au and then was transformed to the β-AuZn (cubic phase, JCPDS 30-0608) compound in the bottom side of the solder. As aging time increased, γ-Ni 5 Zn 21 (cubic phase, JCPDS 06-0653) compounds were formed on the Ni layer. Finally, the Ni 5 Zn 21 phase divided by three layer was formed with grains of columnar shape, and the thickness of the layers was changed by aging time.