Inhomogeneous Interfacial Layer: A Hidden Cause of High Thermal Contact Resistance in Polymer-Based Thermal Interface Materials with Spherical Fillers

Polymer-based thermal interface materials (TIMs) are widely employed in modern electronic devices for the enhancement of heat dissipation. With highly conductive fillers, the thermal conductivity of TIMs far surpasses that of their polymer counterparts, reaching several tens of W/(m·K). However, with increasing thermal conductivity and lower bond line thickness, the thermal contact resistance (TCR) at the interface becomes a bottleneck, limiting the heat dissipation efficiency of TIMs. Herein, the origin of the unexpectedly high TCR in polymer-based TIMs with spherical fillers was explored through combined experimental and computational studies. The lower bound of TCR from different experiments is around 1 × 10^-6 m²·K/W, significantly higher than the theoretical value from molecular dynamics. Further simulations and experiments demonstrate the existence of a microscopic inhomogeneous interfacial layer, where a higher ratio of polymer near the surface leads to much smaller thermal conductivity than that of the bulk TIM. Such a polymer-rich layer induces significant thermal resistance and is included in the TCR during experimental measurements. This finding provides insight into the intrinsic factors limiting the thermal performance of TIMs and highlights potential strategies to optimize the design of TIMs for enhanced thermal management in electronic devices.