Effect of adding Ag to the medium entropy SnBiIn alloy on intermetallic compound formation

Wetting reactions of the medium entropy alloy of SnBiIn and SnBiInAg on Cu substrate have been investigated. The melting points of both SnBiIn and SnBiInAg are about 80 °C. The reactions were performed at 120 °C, 140 °C, and 160 °C. The kinetics of interfacial intermetallic compound (IMC) growth of Cu₆Sn₅ was studied to be ripening-controlled with activation energy about 11.1 kJ/mol for SnBiIn and 10.4 kJ/mol for SnBiInAg. However, the addition of Ag has effectively reduced the IMC growth by 20–30%. We propose that it is because Ag has reduced the pre-factor of diffusivity by increasing the entropy of the alloy.