Characterization of intermetallic compounds formed during the interfacial reactions of liquid Sn and Sn-58Bi solders with Ni substrates

The intermetallic compound that appears during the soldering reaction between pure Sri and Ni substrate at temperatures ranging from 250 to 400 degreesC is analyzed to be Ni43Sn57, A similar reaction at the Sn-58Bi/Ni interface results in the formation of the Ni41.5Sn57.9Bi0.6 phase. At the Sn/Ni and Sn-58Bi/Ni inter-faces, each kind of intermetallic compound formation exhibits a similar scallop-type morphology. However, the growth rate of intermetallic compounds at the Sn/Ni interface is greater than that at the Sn-58Bi/Ni interface. The growth kinetics for both cases is diffusion controlled. The activation energy for the intermetallic growth at the Sn/Ni interface is 43.7 kJ/mol, which is higher than that at the Sn-58Bi/Ni interface (28.3 kJ/mol).