Intermetallic compound layer formation between copper and hot-dipped 100In, 50In-50Sn, 100Sn,and 63Sn-37Pb coatings

The growth kinetics of intermetallic compound layers formed between four hot-dipped solder coatings and copper by solid state, thermal aging were examined. The solders were l00Sn, 50In-50Sn, 100In, and 63Sn-37Pb (wt.%); the substrate material was oxygen-free, high conductivity Cu. The total intermetallic layer of the 100Sn/Cu system exhibited a combination of parabolic growth at lower aging temperatures and t^0.42 growth at the higher temperatures. The combined apparent activation energy was 66 kJ/mol. These results are compared to the total layer growth observed with the 63Sn-37Pb/Cu system which showed parabolic kinetics at similar temperatures and an apparent activation energy of 45 kJ/mol. Both 100Sn and 63Sn-37Pb diffusion couples showed a composite intermetallic layer comprised of Cu₃Sn and Cu₆Sn₅. The intermetallic compound layer formed between In and Cu changed from a CuIn₂ stoichiometry at short annealing times to a Cu₅₇In₄₃ composition at longer periods. The growth kinetics were parabolic with an apparent activation energy of 20 kJ/mol. The intermetallic layer growth of the 50In-50Sn/Cu system exhibited extreme variations in the layer thicknesses which prohibited a quantitative assessment of the growth kinetics. The layer was comprised of two compounds: Cu₂₆Sn₁₃In₈ which was the dominant phase and a thin layer of Cu₁₇Sn₉In24 adjacent to the solder.