The growth behavior of the intermetallic compounds that formed at the interfaces between Sn-Ag-Bi-In solders and Cu substrates during solid-state aging is investigated. The compositions of the intermetallic compounds are Cu-3(Sn,In) near the Cu substrates and Cu-6(Sn,In)(5) near the solders; very little Bi or Ag was dissolved in the compounds. The aging temperatures were 120A degrees C, 150A degrees C, and 180A degrees C for 5 days, 10 days, 20 days, and 40 days. The change in the morphology of Cu-6(Sn,In)(5) from scallop type to layer type was prominent at the aging temperature of 180A degrees C. The thickness of the compound layers did not vary much at the lower aging temperatures but followed the diffusion- controlled mechanism at 180A degrees C. Massive Kirkendall voids were observed in Cu-3(Sn,In) layers at the aging temperature of 180A degrees C.
