Dissolutive wetting process and interfacial characteristic of molten Sn–17Bi–0.5Cu alloy on copper substrate

The reactive spreading processes of Sn–17Bi–0.5Cu melt alloy on Cu substrate were studied by sessile drop method in the temperature range of 523–673 K. Dynamic contact angles between the solder and Cu substrate at different times were recorded with high-resolution CCD digital video. The smallest contact angle was observed at 623 and 673 K. Ultimate spreading radius does not increase monotonously with the temperature increasing. These can be attributed to the strong dissolution of Cu substrate into the liquid solder, which hinders the solder from spreading. Triple line area configuration of the Sn–17Bi–0.5Cu/Cu system was discussed by the description of the equilibrium state. The calculated results based on experiments of the tension balances along each of the three interfaces show good agreement with theoretical analysis. Intermetallic compounds at the Sn–17Bi–0.5Cu/Cu interface are identified as Cu6Sn5 adjacent to the solder and Cu3Sn adjacent to the Cu substrate, respectively. These results are of practical interest for composite lead-free solders’ preparations and joining of Sn–17Bi–0.5Cu to Cu substrate.