Effects of copper doping on microstructural evolution in eutectic SnBi solder stripes under annealing and current stressing

Effects of Cu doping on the microstructural evolution in the eutectic SnBi solder stripes under annealing and current stressing were investigated. Coarsening of the Bi grains was observed in the eutectic SnBi solder upon annealing at 85 degrees C. Doping of 1 wt.% Cu could significantly reduce the grain coarsening rate from 2.8 to 0.5 mu m(3)/h. In addition to grain coarsening, mass accumulation of Bi at the anode and solder depletion at the cathode of the eutectic SnBi solder stripe stressed by a current of 1.3 x 10(4) A/cm(2) at 85 degrees C were also observed. Doping of I wt.% Cu could also reduce the grain coarsening of the solder under current stressing; however, it resulted in an enhancement of the electromigration effect. Accumulation of Bi at the anode and the solder depletion at the cathode became more severe in the Cu-doped solder stripe.