Intermetallic compound layer growth at the interface between Sn–Cu–Ni solder and Cu substrate

Abstract

Phase analysis and growth kinetics of intermetallic compound (IMC) layers formed between low cost Sn–Cu–Ni solder for wave soldering and Cu substrate by solid state isothermal aging were examined at temperatures between 80 and 150 °C for 0 to 60 days. The IMC layer was composed of two phases; Cu 6Sn 5 (also (Cu,Ni) 6Sn 5) adjacent to the solder, Cu 3Sn adjacent to the copper. The Cu 3Sn layer was absent at all time periods for the aging temperatures of 80 and 100 °C. After isothermal aging at 120 °C for 30 days and at 150 °C for all time periods, the solder/Cu interface exhibited a duplex structure of Cu 6Sn 5 and Cu 3Sn intermetallics. From the EPMA analysis, a comparatively high Ni concentration is found between the Cu 6Sn 5 and Cu 3Sn layer. The Ni concentration in the (Cu,Ni) 6Sn 5 intermetallic was about 4.3 at.%. The total IMC layer thickness was approximately 11.5 μm after 60 days of aging at 150 °C. The apparent activation energies for growth of total and Cu 6Sn 5 IMC layer were 76.17 and 66.35 kJ/mol, respectively.