Coupling Effect of the Interfacial Reaction in Co/Sn/Cu Diffusion Couples

Co/Sn/Cu sandwich couples formed by electroplating were examined to investigate the interaction between Cu and Co across the Sn layer for various Sn thicknesses from 75 mu m to 580 mu m. At the Sn/Cu interface, both Cu(6)Sn(5) and Cu(3)Sn are formed. Unlike in a binary Sn/Cu couple, Cu(6)Sn(5) has a spiked structure for couples with a thinner Sn layer. At the Co/Sn interface, two phases, CoSn(3) and (Cu,Co)(6)Sn(5), were simultaneously observed after reaction at 200A degrees C. Remarkably, the CoSn(3) reaction layer was much thinner than that in the binary Sn/Co couple. Furthermore, only the (Cu,Co)(6)Sn(5) phase was formed at 150A degrees C. This finding indicates that CoSn(3) growth is significantly inhibited in Co/Sn/Cu sandwich couples due to the Cu substrate.