A Comparison Study of Cu Dissolution Mechanism and Kinetics in Solder Joints under Electromigration and Extended Reflow

Comparisons of Cu dissolution mechanism and kinetics between solder joints under electromigration (EM) and extended reflow have been studied. Cu consumption rate varies significantly from joint to joint under identical EM stressing, while not much such variations under extended reflow. This is related to the Cu diffusivity difference through anisotropic Sn grains under EM. Both Cu dissolution kinetic parameter n and activation energy Q are different between EM and extended reflow. Under EM, the controlling process for Cu dissolution could be cathode side Cu6Sn5 reaction with n=1 and Q=0.79 ev/atom. Under extended reflow, the controlling process can be Cu diffusion through IMC grain boundaries or molten Sn channels between IMC grains, with n=0.5 and Q=0.36 ev/atom.