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/Ni20Co 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 Ni3Sn4 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.