Mechanical behavior of microelectronics and power electronics solder joints under high current density: Analytical modeling and experimental investigation

This dissertation focuses on the mechanical reliability of microelectronics solder joints under high density electric current stressing. It contains both experimental and analytical modeling parts.; In the experimental part, high density current stressing experiments were conducted using flip-chip and Ball Grid Array (BGA) test vehicles. In addition to electromigration, thermomigration is also studied and observed. The major failure mechanism is identified as the void nucleation and growth due to the combined effects of electromigration and thermomigration. Nano-indentation tests show that the elastic modulus of a solder joint degrades during current stressing. A Pb phase coarsening model that includes the influence of current density is proposed. The Moire Interferometry technique is used to measure the in-situ displacement evolution of BGA solder joints under electric current stressing.; In the analytical modeling part, a diffusion-mechanical coupled stress-current density constitutive model for solder alloy under electromigration is presented. The constitutive model is numerically implemented into FEM code to simulate the displacement fields of the BGA lead-free solder joints under current stressing. Despite all of the assumptions and simplifications employed in the simulation, it predicts reasonably close displacement results to the Moire Interferometry experimental results in both spatial distribution and time history evolution. This indicates that the electromigration model is reasonably good at predicting the mechanical behavior of lead-free solder alloy under electric current stressing.