Electromigration in Sn-Bi Modified with Polyhedral Oligomeric Silsesquioxane

Abstract

Electromigration (EM) behavior of eutectic Sn-Bi modified with cage-type polyhedral oligomeric silsesquioxane (POSS) trisilanol was investigated. A direct current (DC) was applied to solder joints newly designed for uniform current distribution throughout the joint. For this study, a current density of 104 A/cm2 was applied at 25°C and 50°C. The evolution of surface and interior microstructure due to current stressing was observed periodically using optical and scanning electron microscopy. The results revealed that the EM behavior was retarded significantly in solder joints with the addition of POSS trisilanol. Different from eutectic Sn-Bi solder joints, no continuous hillocks formed at the anode side and no cracks occurred at the cathode side in solder joints modified with POSS trisilanol even after 336 h of current stressing at 25°C. In addition, the accumulation of Bi/Sn phases at regions near the anode/cathode was also effectively limited. Joints stressed at 50°C also exhibited similar behavior. It is postulated that POSS trisilanol near the phase boundary provided significant restriction to the mass transport due to DC current stressing.