Electric current effect on microstructure of ball grid array solder joint

The electric current effect on the microstructure of ball grid array (BGA) solder joint was investigated at room temperature with current density of the order of 102 A/cm2. Sandwich-like samples of 'Au/Ni/Cu pad-Sn37Pb solder ball-Au/Cu pad' structure were used for current stressing with different time/current density combinations. Extensive dissolution of pad metal, massive formation of (Cu, Ni)6Sn5 and Cu3Sn intermetallic compounds (IMC), slight accumulation of (Cu, Ni)6Sn5 IMC, nucleation of large dendrite of (Cu, Ni)6Sn5 IMC, localized dissolution of the pad metal, as well as melting of the solder joint were observed for different cases, which can be ascribed to joule heating produced by the electric current flow in the circuit. A compositional gradient-controlled solid-state diffusion process with assistance of electromigration was suggested for a current density of 3.0 × 102 A/cm2. And, a reaction-dominated liquid-state dissolution process at very high temperature caused by joule over-heating occurred for 4.5 × 102 A/cm2. Super-heating induced instant break down of the solder joint and/or circuit break was found for 6.0 × 102 A/cm2.