Effects of surface finishes and current stressing on the interfacial reaction characteristics of Sn–1.2Ag–0.7Cu–0.4In solder bumps

The effects of surface finishes on the in situ interfacial reaction characteristics and electromigration (EM) reliabilities of ball grid array (BGA) Sn–1.2Ag–0.7Cu–0.4In lead-free solder bumps were investigated under annealing and EM test conditions of three different temperatures, 135 °C, 150 °C, and 170 °C, with a constant electrical current density of 5.0 × 103 A/cm2. The activation energies of total intermetallic compounds (IMCs) were found to be 0.87 eV for electroless nickel–immersion gold (ENIG) and 0.86 eV for organic solderability preservatives (OSP). The ENIG finish appeared to act as an effective diffusion barrier between the Cu substrate and the solder, which leads to better EM reliability in comparison with Cu-based pad systems. The failure mechanisms were explored in detail via in situ EM tests.