Reactivity between Sn-Ag Solder and Au/Ni-Co Plating to Form Intermetallic Phases

For the formation of micro joint not to melt by secondary reflow soldering, we tried to enhance the reactivity of Sn-Ag solder with Au/Ni-20Co plating. It was confirmed that the addition of Co in Ni and existence of Au plating effectively accelerated the reaction and the Sn-Ag solder completely transformed to the intermetallic compounds with a higher melting temperature. Particularly, the addition of Co in Ni changed the interfacial reaction layer from Ni 3 Sn 4 to (Ni,Co)Sn 2 with higher diffusivity of Ni which enhanced the formation of the intermetallic phases. This process is expected to replace the packaging technology using high temperature solders.