Numerical Investigation on Electromigration Oriented Failure of Lead Free Solder Joints With Aging Effects

Abstract

Abstract Lead free solder materials have replaced lead based solder materials nowadays for increased environmental concern. Further miniaturization of electronic solder joints in packages has caused electromigration to dominate among all the reliability issues found in electronic packages. This current investigation deals with the review of mechanical property degradations of SAC305(Sn-96.5Ag-3.0Cu-0.5) solder materials due to thermal aging and their effects on electromigration oriented failure of small scale flip chip solder bumps. Thermal aging causes significant degradation of ultimate strength as well as elastic modulus of the SAC solder material. This degradation in stress-strain relationship plays an utterly important role in electromigration oriented mass diffusion and subsequent failure in the solder joints. This research highlights the linkage between thermal aging oriented strength degradation and its effect on electromigration oriented void propagation rate and time to failure. Structural-electric diffusion analyses with a finite element analysis software have been performed and results derived from different aging conditions (1 to 60 days of aging at 100 °C) at different electromigration temperatures have revealed that mass diffusion due to electromigration and associated stress migration actually reduces with the increment of aging time and thus increases time to failure in case of a flip chip solder joint. Simulation results have been found to be in good agreement with the experimental results available in literatures. These results can pave way to further detailed experimental investigation on effect of thermal aging on electromigration.