Current stressing effect on interfacial reaction characteristics of Cu pillar/Sn-3.5Ag microbumps for 3D integration

The paper presents the current stressing effect on interfacial reaction characteristics of Cu pillar/Sn-3.5Ag microbumps for 3D integration, which is quantitatively evaluated by using in-situ scanning electron microscopy (SEM). Results show that Cu₆Sn₅ and Cu₃Sn phases are formed with similar thickness at both the interface between the Cu pillar and the Sn-3.5Ag solder; intermetallic compound (IMC) growth followed a linear relationship with the square root of the annealing time due to a diffusion-controlled mechanism, but the IMC thickness increases linearly with current-stressing time, controlled by a chemical reaction dominant mechanism; and the transition time of IMCs growth during stressing condition grew faster than under the annealing condition because electron wind force enhanced IMC growth.