Effect of grain orientation on electromigration degradation in lead-free solder joints

EM degradation mechanisms were closely related to Sn-grain orientations at the interface. In multi-grain Sn0.7Cu joints, the Cu plate hollow crack at the cathode caused by the rapid dissolution of cathode IMC and Cu interstitial diffusion to anode lead to electrical failure at an early stage, when the c axis is roughly aligned with the electrical current. Single-grain structure with layered twinning usually appeared in Sn3.0Ag0.5Cu solders, most of them had c axis roughly at a right angle relative to the current direction, in which the rates of IMC dissolution was slow. significant grain structure change are observed in Sn3.0Ag0.5Cu solder joint During EM stress, after EM the number of grain increased with size reduced, twin orientation relationship was weakened and misorientation angle became uniform.