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 120°C, 150°C, and 180°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 180°C. The thickness of the compound layers did not vary much at the lower aging temperatures but followed the diffusioncontrolled mechanism at 180°C. Massive Kirkendall voids were observed in Cu 3 (Sn,In) layers at the aging temperature of 180°C.

This investigation elucidates stress evolution in situ in tin strips under electromigration using synchrotron radiation x-ray. Minute variations in stress are determined precisely using intense x-rays. Back stresses gradient with the values of 5.5 and 16.5 MPa/cm, which are induced by the current densities of 1 × 103 and 5 × 103 A/cm2, respectively, are measured directly. The effective diffusivities that include both grain and lattice diffusion at various current densities are determined. The Joule heating is observed, ranging from 5 to 15 °C, according to various current densities passed through the stripes. Results of this study suggest that the protective oxide layer on the surfaces significantly influences the kinetics of stress evolution.