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 fo ur hot-dipped solder coatings and copper by solid state, thermal aging were examined. The solders were 100Sn, 50In-50Sn, 100In, and 63Sn-37P b (wt.%); the substrate material was oxygen-free, high conductivity Cu . The total intermetallic layer of the 100Sn/Cu system exhibited a com bination of parabolic growth at lower aging temperatures and t0.42 gro wth at the higher temperatures. The combined apparent activation energ y 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 interm etallic layer comprised of Cu3Sn and Cu6Sn5. The intermetallic compoun d layer formed between In and Cu changed from a CuIn2 stoichiometry at short annealing times to a Cu57In43 composition at longer periods. Th e 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 compr ised of two compounds: Cu26Sn13In8 which was the dominant phase and a thin layer of Cu17Sn9In24 adjacent to the solder.