Solid-State Reactions of Silver and Aluminum Associated with Silver Wire Bonds

In recent years, Ag alloy wire has attracted great interest as a novel bonding material to replace the conventional Au wire bonding. Ag wire has the advantages of great workability, high electrical conductivity and low growth rate of intermetallic compound at bonding interface. However, in literatures, studies on mechanisms of the growth of Ag-Al intermetallic compounds and their impact on bonding failure are rather limited. In this study, the growth behavior of the Ag-Al intermetallic compounds during the solid-state reactive diffusion in Ag/Al/Si bonding system was investigated. The Ag/Al/Si layered structure was prepared by using e-beam deposition technique and annealed at temperatures of 200-400°C for various times. Two types of intermetallic compound layers formed at the Ag/Al interface and were identified as Ag3Al and Ag2Al. The phase evolution of Ag3Al and Ag2Al was quantitatively analyzed by scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDX) and by using the phase diagram of binary Ag-Al. After thermal aging at 400°C, cracks formed at the interface between the Ag2Al intermetallic compounds and Si substrates. The formation mechanisms of the Ag2Al and Ag3Al intermetallic compounds are proposed, and the growth kinetics of Ag-Al intermetallic compounds are discussed in this study.