Atomic migration in eutectic SnBi solder alloys due to current stressing

Current stressing at densities from 2.9 to 7.3 × 10⁴ A/cm² has significant effects on the atomic migration of eutectic SnBi solder alloys. At lower density (2.9 × 10⁴ A/cm²), electromigration dominates the migration of both Sn and Bi, and drives Sn and Bi atoms to migrate toward the anode side. While at higher densities (4.4 and 7.3 × 10⁴ A/cm²), the enhanced Bi electromigration induces a back stress, which promotes a reversed migration of Sn toward the cathode side. A large number of Sn atoms accumulate at the cathode side and form lumps there.