Effect of bonding time on the microstructure and mechanical properties of Co/Sn/Cu joint

The bonding process of Co/Sn/Cu couple has been conducted at 270 °C. The microstructure evolution was observed. The spreading test of Cu/Sn– x Co and Co/Sn– x Cu was conducted to explain the microstructure evolution of Co/Sn/Cu couple. The results showed that the main interfacial intermetallic compounds (IMCs) layer of Cu/Sn side of Co/Sn/Cu couple was (Cu, Co) 6 Sn 5 , as the dissolution of Co from Co substrate to solder layer. The (Cu, Co) 6 Sn 5 IMCs layer only thickened slightly during bonding process as large amount of the (Cu, Co) 6 Sn 5 IMCs layer dissociated into solder alloy layer. As the adsorbing effect of Co substrate on the dissociating (Cu, Co) 6 Sn 5 IMCs, there was a thick (Cu, Co) 6 Sn 5 IMCs layer covered on the surface of Co substrate at the early stage of bonding process. For longer bonding time (> 30 min), the (Co, Cu)Sn and (Co, Cu)Sn 3 IMCs generated on the Co/(Cu, Co) 6 Sn 5 interface as the diffusion of Sn atom from liquid solder alloy to Co/(Cu, Co) 6 Sn 5 interface. The Co/Sn/Cu joint bonded for 60 min could work at the temperature of 300 °C. The shear strength of joints bonded for 20 and 30 min was approximate 45 MPa. The shear strength of joints bonded for a time more than 30 min declined gradually as the generation of (Co, Cu)Sn 3 IMCs.