Characterization of Electrical Current Stress and Indentation Creep of Carbon Nanotubes- reinforced Low Melting Temperature Sn-58Bi Composites

Abstract

Sn-58Bi eutectic alloy emerges as one of the potential lead-free solder material candidates due to its low melting temperature that enables low temperature soldering reflow process during the manufacturing of fine-pitch and low z-height advanced microelectronic devices. Its low melting temperature provides feasible solution for a two-step reflow process in the assembly of 3D-stacked advanced packaging technology, and at the same time reduces dynamic warpage-induced quality and reliability issues. However, miniaturization of these microelectronic devices has triggered significant reliability risk to its solder interconnects due to the requirement of high current density that resulted in severe physical failures, such as electromigration (EM), and thermomigration (TM). To mitigate the risk, carbon nanotubes (CNT) are incorporated into elemental Sn and Bi powders using planetary ball milling technique, and subject to liquid phase melting to form low melting temperature CNT- reinforced eutectic Sn-58Bi composites. Electrical resistance and current density of the eutectic alloy and its composites were investigated, and results show that Sn-58Bi-0.03CNT composite has the lowest electrical resistance and was able to survive 26 times longer duration of current stressing, even with the supply of higher stressed current. Creep performance of eutectic Sn-58Bi system was also examined in this study due to its high homologous temperature of 0.72 at room temperature. Marginal improvement in indentation creep performance was seen in the composites.