Polyimide-Densified BNNS/ANF Composite Films With Synergistically Enhanced Thermal Conductivity and Mechanical Properties

Miniaturized and integrated high-frequency flexible electronics for artificial intelligence (AI) with high computational requirements demand high-performance thermal interface materials (TIMs). The composite films made by adding boron nitride nanosheets (BNNS) fillers into aramid nanofibers (ANF) have garnered considerable research interest, primarily owing to superior heat conduction and favorable insulating performance. However, the abundant nanopores in BNNS/ANF films not only limit further improvement in thermal conductivity but also compromise mechanical integrity. Herein, using vacuum filtration and densification by polyimide (PI), we fabricated a structurally dense and performance-optimized PI/BNNS/ANF composite film. Experimental results show that this structurally optimized material significantly improves thermal conductivity, reaching 10.78 W m −1 K −1 (a 33.3% increase) and mechanical strength (32 MPa, a 29.1% increase) over the films without PI densification, while retaining excellent dielectric properties characterized by low permittivity and minimal dielectric dissipation. This study confirms that the introduction of PI is highly effective in boosting the comprehensive performance of BNNS/ANF composite films, providing a new solution for high-performance TIMs in compute-intensive AI. Highlights Composite films were successfully prepared via polyimide densification. The composite films exhibit a dense and continuous microstructure. Both thermal and mechanical properties are improved. Simulation results verify the reduction in interfacial thermal resistance. Low dielectric constant and low dielectric loss were maintained.