Electromigration in eutectic In-48Sn ball grid array (BGA) solder interconnections with Au/Ni/Cu pads

In this study, the microstructural evolution and interfacial reactions of the eutectic In-48Sn BGA solder bump interconnection with Au/Ni/Cu pads—under current stressing of 0.7 × 10⁴ A/cm² at ambient temperatures of 25 and 55 °C for up to 720 h—have been investigated. During electromigration, tin (Sn) acted as the “dominant diffusing species” and migrated from cathode to anode, while indium (In) migrated from anode to cathode. Finally, the phase segregation of Sn and In occurred. Sn-rich and In-rich layers accumulated at the anode side and cathode side of the solder bump, respectively. Due to the influence of current stressing, the simultaneous growth of the interfacial inter-metallic compounds (IMCs), at both the anode interface and the cathode interface, was accelerated. The anode IMC grew faster than the cathode IMC. By raising the ambient temperature, both the phase segregation and the interfacial IMC growth were enhanced. Based on the accumulation rate of the Sn-rich layer, which was calculated to be 7.85 × 10⁻¹⁰ cm/s at 25 °C and 2.07 × 10⁻⁹ cm/s at 55 °C, respectively, the products of the diffusivity and the effective charge number (DZ*) of Sn in In-48Sn solder was determined to be 1.17 × 10⁻¹⁰ cm²/s at 25 °C and 3.39 × 10⁻¹⁰ cm²/s at 55 °C, respectively.