Dry-Contact Thermal Interface Material with the Desired Bond Line Thickness and Ultralow Applied Thermal Resistance

Abstract

Efforts to directly utilize thixotropic polymer composites for out-of-plane thermal transport applications, known as thermal interface materials (TIMs), have been impeded by their mediocre applied thermal resistance (R_eff) in a sandwiched structure. Different from traditional attempts at enhancing thermal conductivity, this study proposes a low-bond line thickness (BLT) path for mitigating the sandwiched thermal impedance. Taking the most common TIM, polydimethylsiloxane/aluminum oxide/zinc oxide (PDMS/Al₂O₃/ZnO), as an example, liquid metal is designed to on-demand localize at the Al₂O₃-polymer and Al₂O₃-filler interface regions, breaking rheological challenges for lowering the BLT. Specifically, during the sandwiched compression process, interfacial LM is just like the lubricant, dexterously promoting the relaxation of immobilized PDMS chains and helping fillers to flow through mitigating the internal friction between Al₂O₃ and adjacent filler. As a result, this TIM first time exhibits a boundary BLT (4.28 μm) that almost approaches the diameter of the maximum filler and performs an ultralow dry-contact R_eff of 4.05 mm² K/W at 40 psi, outperforming most reported and commercial dry-contact TIMs. This study of the low-BLT direction is believed to point to a new path for future research on high-performance TIMs.

Keywords: interface; liquid metal; rheology; thermal interface material; thermal resistance.