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Effect of heat treatment on the interfacial adhesion strength between Sn-Zn-xAg lead-free solders and Cu substrate

Sn-9Zn eutectic solder alloy is a potential candidate to replace 63Sn-37Pb alloy as interconnecting material in the electronic packaging industry, but the inferior wettability and poor oxidation resistance make this alloy unsuitable for wide application. In this study, different Ag contents were added to the Sn-9Zn alloy to improve the wettability, oxidation resistance, and adhesion strength at the interface. A pull-off test was used to estimate the adhesion strength of the interface between Sn-Zn-xAg solders and Cu substrates, scanning electron microscopy (SEM) was utilized to observe the fracture morphology, and energy dispersive spectrum (EDS) was employed to analyze the distribution of elements. Finally, X-ray diffraction (XRD) was exploited to identify the intermetallic compounds (IMCs) formed at the interface.