Probing the Scaling Effect on Electromigration and Segregation in Sn–58Bi Solder Interconnects Through Numerical Modeling

In this brief, a phase field model is developed to study the length-dependent behavior of phase electromigration and segregation in Sn–58Bi solder interconnects under electric current stressing, especially accounting for the stress effect induced by back flow. Simulation results of Bi atom migration and Bi-rich phase segregation on the anode side are in good agreement with experimental results, and the increase rate of the Bi-rich phase layer thickness is smaller for a shorter interconnect, leading to formation of thinner Bi-rich phase layer. Thicker Bi-rich phase layer in a longer interconnect results in a larger increase in voltage across the interconnect. The Bi atom migration rate is inversely proportional to the length of solder interconnects. It is revealed that the directional diffusion toward the anode is suppressed in shorter interconnects due to larger back stress flow, resulting in less segregation of the Bi-rich phase near the anode side.