Influence of microstructure inhomogeneity on the electromigration behavior of flip chip solder joints

With increasing miniaturization of electronic devices and systems, the dimension of solder joints and pitches has been continuously scaling down, while the current density carried by solder joints increasing significantly, consequently a critical issue, electromigration (EM), has become a key reliability concern. The EM behavior in the joint is mainly dependent on the magnitude and distribution of the current density and thermal gradient. In this study, thermo-electrical finite element analysis was employed to characterize the influence of microstructure inhomogeneity on the current density and thermal gradient in micro-scale eutectic SnPb (63Sn37Pb) solder joints. Results show that, both geometry factor and microstructure inhomogeneity have obvious influence on the distribution of current density and thermal gradient in the flip chip solder joint. The current density, current crowding ratio and thermal gradient in the Sn-rich phase are much larger than that in the Pb-rich phase, thus the Pb atoms in Sn-rich phase are more prone to migrate under current stressing.