Electromigration-induced Bi segregation in eutectic SnBi solder joint

Effects of current stressing of 6.5 x 10(3) A/cm(2) on the eutectic SnBi solder joint at 70 degrees C were investigated. The Bi segregation at the anode side was found, and the Bi segregation layer grew with the increasing stressing time. The Bi segregation may result in the strength reduction and the more serious Joule heating due to the brittleness and the higher resistivity of Bi, respectively. Effects of the solder microstructure and the current density on the Bi segregation were also investigated. By preannealing the solder joint at 120 degrees C for 192 h to 360 h before current stressing, the growth rate of the Bi segregation layer was significantly reduced due to the reduction of the density of the interphase boundary. The layer growth rate was also greatly reduced by reducing the current density from 6.5 x 10(3) A/cm(2) to 5 x 10(3) A/cm(2).