Interfacial reaction in Cu/Sn/Cu system during the transient liquid phase soldering process Original Research Article

A thin interlayer of pure Sn foil has been sandwiched between two pieces of Cu foil base metal and reflowed at 260, 300 and 340 °C, under 2%H2/98%N2 forming gas, for 5 – 480 min. We report here: (i) the interfacial microstructures to show Cu6Sn5 scallops and Cu3Sn columnar crystals; (ii) the pronounced difference in the thicknesses of the Cu6Sn5 and Cu3Sn layers formed at the two original boundary planes in the Cu/Sn/Cu samples; (iii) the diffusion-kinetic constants for the Cu6Sn5 and Cu3Sn growth derived from the Cu/Sn/Cu samples for a range of Sn interlayer thicknesses; and (iv) a type of grain boundary/molten channel-controlled growth of Cu6Sn5 with a time dependence similar to that for the volume diffusion-controlled growth. These results provide new insight into the mechanism and kinetics of the interfacial reaction between liquid Sn and solid Cu, and other similar metallic liquid/solid systems.