Aging effects on interfacial reactions between Cu addition into the Sn-9Zn lead-free solder and Au substrate

This study investigates aging effects on interfacial reactions between Sn-9wt%Zn-x wt% (SZ-xCu) alloys and Au substrate. The Au₃Zn₇/AuZn₂/AuZn and Au₃Zn₇/AuZn phases respectively formed in the SZ/Au and SZ-1Cu/Au couples aged at 160°C for 24 hours. Only the AuSn phase was found at the SZ-4 Cu/Au interface. Extending the aging time to 800 hours, Sn became a dominant diffusion element. Binary Au-Sn phases and the metastable Au-Zn-Sn ternary phase, Au_33-36 Zn_35-36Sn_29-31, was formed at the interface. The aging effect causing the changes of dominant diffusion element and concentration of Zn, Cu in the solder is the main reasons to change the sequence of the IMC formation in the SZ-xCu/Au systems.