Microstructure growth morphologies, macrosegregation, and microhardness in Bi–Sb thermal interface alloys.

Abstract

Due to the rising demand for thermal management technologies within the electronics industry, there has been an increased emphasis on developing new thermal interface materials (TIMs) with enhanced performance. Despite Bi-based alloys having exhibited promising potential as TIMs in microelectronics cooling applications, understanding the microstructure evolution of these alloys and the consequent effects on the resulting properties still remains an essential task to be accomplished. Herein, a directional solidification technique is used to investigate microstructural features and Vickers microhardness of Bi(5–20) wt% Sb alloys with a focus on the roles of alloy composition, solidification thermal parameters, and macrosegregation. The results show the formation of aligned Bi-rich den-drites in a broad range of cooling rates from about 0.2 to 25 C s1. In contrast, as the alloy Sb content increases, two morphological transitions in the Bi-rich matrix are shown to occur as follows: trigonal pattern ! irregular shape ! trigonal pattern. Then, primary and secondary dendritic arm spacings are related to growth and cooling rates through experimental equations. Finally, the occurrence of macrosegregation along the length of the Bi–20 wt% Sb alloy casting is shown to be a key factor associated with the variation of microhardness.