Solid-state interfacial reactions at the solder joints employing Au/Pd/Ni and Au/Ni as the surface finish metallizations

Abstract A tri-layer of nickel/palladium/gold (Au/Pd/Ni) is a promising candidate to replace the conventional Au/Ni bi-layer as the surface finish metallization for lead-free packaging. A surface finish metallization (Au/Pd/Ni or Au/Ni) and a Sn layer are sequentially deposited on a Cu substrate and then are subjected to thermal aging at 150 and 200 °C to investigate the interfacial reactions in the stacking multilayer structure made by low-temperature solid-state bonding. Because of the absence of the reflow process, the Pd and Au layers do not dissolve in the Sn matrix but remain at the interface and participate in the interfacial reaction to form the (Pd,Ni,Au)Sn 4 and (Au,Ni)Sn 4 phases at the Au/Pd/Ni- and Au/Ni-based interfaces, respectively. Though the Pd layer was only 0.4 μm, its resulting (Pd,Ni,Au)Sn 4 phase is much thicker than the (Au,Ni)Sn 4 phase. These two intermetallic compounds exhibit very different microstructural evolution which significantly affects the interfacial microstructures and growth rate of other intermetallic compound formed at the same interfaces.