Electromigration in Line-Type Cu/Sn-Bi/Cu Solder Joints

Abstract

In this study, the different electromigration (EM) behaviors of eutectic Sn-Bi solder in the solid and molten states were clarified using line-type Cu/Sn-Bi/Cu solder joints. When the eutectic Sn-Bi solder was in the solid state during the EM test, a Bi-rich layer formed at the anode side while a Sn-rich band formed at the cathode side, and the intermetallic compound (IMC) at the cathode side was thicker than that at the anode side. The growth of the Bi-rich layer exhibited a linear dependence on the time of stressing. While the actual temperature of the solder joint increased to 140°C and the solder was in a molten state or partially molten state, two separate Bi-rich layers formed at the anode side and a great many Cu 6 Sn 5 IMC precipitates formed between the two Bi-rich layers. Also, the IMC layer at the cathode side was thinner than that at the anode side. With a current-crowding-reduced structure, the products of diffusivity and effective charge number of Bi in the eutectic Cu/Sn-Bi/Cu solder joints stressed with current density of 5 9 10 3 A/cm 2 at 35°C, 55°C, and 75°C were calculated.

Failure mechanisms of solder interconnects under current stressing in advanced electronic packages

“…Also, the n for Pb-rich phase growth in our study was approximately 3.28, which corresponded to the co-kinetics of grain boundary and volume diffusion [26]. Similar to eutectic SnPb solder, current stressing-enhanced Bi coarsening was also detected in SnBi solder joints in our group [20].…”

“…To measure the displacement driven by EM, inert particles or nanoindentations have been used as surface markers, which moved in the opposite direction to the EM flux as expected. Also, the product for the migration of Bi was investigated [20]. Table 2 lists the DZ Ã values obtained for a Sn58Bi solder under different test conditions.…”

Influence of pre-existing void in the solder joint on electromigration behavior of Cu/Sn58Bi/Cu joints

“…2(c)-(d), respectively. Obviously, Sn and Bi phases became coarse after a longer current stressing, and Bi atoms significantly migrated toward the anode and formed a Bi-rich layer in the front of the anode interface in both solder joints, this is similar to the previous studies [10,11]. The cracks marked in Figs.…”

Retarding the electromigration effects to the eutectic SnBi solder joints by micro-sized Ni-particles reinforcement approach

“…Furthermore, grain boundaries form a network that passes through the entire specimen [25]. As for binary Sn-Bi system, the phaseboundary has been approved to be the fast diffusion channel for the movement of Bi atoms/ions [8,21,26,27]. Accordingly, the finer the Bi phases in lamella microstructure, the greater the phase boundaries in number.…”