Rapid Enhancement of Thermal Conductivity by Incorporating Oxide-Free Copper Nanoparticle Clusters for Highly Conductive Liquid Metal-based Thermal Interface Materials

Abstract

Enhancing thermo-physical properties of thermal interface materials (TIMs) is important for efficient cooling of electronic devices. To eliminate air pockets between silicon (Si) die and copper (Cu) heat spreader/sink, TIMs can fill the voids at the interfaces and reduce the contact resistances. In recent, gallium (Ga)-based liquid metals (LMs) have drawn much attention due to their high thermal conductivity and maintained fluidity at room temperature. Previous works have tried to further increase the thermal conductivity by adding conductive fillers to Ga-based LM matrix; however, it is challenging to attain a solder-level thermal conductivity (>60 Wm−1K−1) while maintaining the fluidity. The fluidity gradually decreases due to the solid additives with high volume fraction (>10%) of fillers and significant oxidation, which is a critical issue for applying the LM TIMs to real-world application. To address the issues mentioned above, we incorporated Cu nano-fillers into the Ga-based matrix, excluding the oxidation issues. Through our suggested method, the fabricated LM composite shows over 64 Wm−1K−1 of thermal conductivity at only 4 vol% of copper nano-fillers. The fluidity can be maintained because of the low vol% of additives, which leads to wetting characteristics for the interface between Si and Cu substrate. The mechanism of thermal enhancement is demonstrated by the cluster visualization test, calculating a nanoparticle clustering model. Through the liquid-cooled test vehicle, the thermal performance of synthesized LM composites is assessed. Approximately 33% lower junction temperature is measured compared to the grease-type TIMs at high heat flux regime (>400 Wcm−2) with excellent thermal stability. In summary, this study not only provides a method for the fabrication of highperformance LM TIMs but also demonstrates the rapid enhancement in thermal conductivity for the thermal management of high-power electronics.