Study on Phase Electromigration and Segregation Behavior of Cu-Cored Sn-58Bi Solder Interconnects under Electric Current Stressing

Cu-cored solder interconnects have been demonstrated to increase the performance of interconnect structures, while the quantitative understanding of the effect of the Cu-cored structure on microstructure evolution and atomic migration in solder interconnects is still limited. In this work, the effect of the Cu-cored structure on phase migration and segregation behavior of Sn-58Bi solder interconnects under electric current stressing is quantitatively studied using a developed phase field model. Severe phase segregation and redistribution of Bi-rich phase are observed in the Cu-cored Sn-58Bi interconnects due to the more pronounced current crowding effect near the Cu core periphery. The average current density and temperature gradient in Sn-rich phase and Bi-rich phase decrease with an increase in the diameter of the Cu core. The temperature gradient caused by Joule heating is significantly reduced owing to the presence of the Cu core. Embedding of the Cu core in the solder matrix could weaken the directional diffusion flux of Bi atoms, so that the enrichment and segregation of the Bi phase towards the anode side are significantly reduced. Furthermore, the voltage across the solder interconnects is correspondingly changed due to the phase migration and redistribution.