Behavior of intermetallics formation and evolution in Ag–8Au–3Pd alloy wire bonds

Highlights: • Two IMC layers formed between Ag–8Au–3Pd alloy wire and Al pad were identified. • IMCs growth during annealing was discussed by diffusion kinetics. • Ag diffusion controls voids filling at bonding interface during thermal aging. -- Abstract: Ag–8Au–3Pd alloy wire has shown promise as an economical substitute for gold wire interconnects from integrated circuits to substrates. This work is undertaken to gain a better understanding on the intermetallic compounds (IMC) formation and evolution at the interface between Ag–8Au–3Pd wire and Al metallization pad. Longitudinal cross-section of bond interface was prepared by dual-beam focused ion beam (FIB) micro-machining for transmission electron microscopy (TEM) analysis. Two intermetallic regions formed at interface were crystallochemically identified as AuAl2 + (Au, Ag)4Al and Ag2Al respectively. Interface evolution tracking by back scattered electron (BSE) imaging showed that IMC initially formed at periphery of bonding area. After short-term annealing treatment (175 °C for 24 h), the voids in the center of the bonding interface shrank and vanished, due to the Ag diffusion played dominant part in IMC growing. The mechanism of IMC formation and evolution at interface was finally elaborated on the basis of thermodynamics and diffusion kinetics respectively