Fluorine‐Mediated Carbon Doping in Boron Nitride: Atomic‐Level Interface Engineering for Balancing Microwave Absorption and Thermal Management

Abstract The advancement of high‐density integrated electronics urgently demands materials that integrate efficient thermal management and microwave absorption. However, conventional design strategies that often rely on materials with multi‐component composites face a trade‐off between these properties, and a lack of microwave absorption effectiveness study in the polymer matrix. Herein, a fluorine‐mediated carbon doping in boron nitride (C‐F‐BN) is designed to achieve atomic‐level interface engineering. Fluoride induces the formation of polarized C─F bonds and promotes ordered sp ² ‐carbon incorporation, which well preserves the BN lattice integrity while establishing strong polarization sites. The resulting C‐F‐BN shows exceptional microwave absorption with a reflection loss of −43 dB at 2 mm thickness, compared to that of only carbon doping in BN, achieving an effective absorption bandwidth of 3.52 GHz and a remarkable absorption efficiency index of 35 dB· GHz mm ⁻¹ . The maintained BN crystallinity, ordered sp ² ‐carbon conversion, and enhanced interfacial compatibility between C‐F‐BN and polyvinyl alcohol (PVA) enable PVA/C‐F‐BN composites to attain higher through‐plane thermal conductivity (0.2599 W·m ⁻¹ ·K ⁻¹ ) at a lower filler loading (5 wt.%). Moreover, the composite exhibits a broader absorption bandwidth of 3.84 GHz with a reflection loss of −32 dB. The design concept offers a feasible route to multifunctional materials for advanced electronic packaging.