Abstract: The miniaturization and high-power density of electronic devices presents new challenges in thermal management. The precise control of microstructure arrangement, particularly in boron nitride nanosheets (BNNS), is essential for achieving efficient heat dissipation in highly thermally conductive composites within electrically insulating package. In this work, manganese ferrite was hydrothermally synthesized on BNNS, creating a layered structure in a magnetically responsive nanohybrid material named BNNS@M. This material was then integrated into a waterborne polyurethane (WPU) solution and shaped under a magnetic field to produce thermally conductive film. By altering the magnetic field direction, the microstructure orientation of BNNS@M was controlled, resulting in anisotropic thermally conductive composite films with horizontal and vertical orientations. Specifically, under a vertical magnetic field, the film 30-Ve-BNNS@WPU, containing 30 wt.% BNNS@M, achieved a through-plane thermal conductivity of 8.5 W m^-1 K^-1 and an in-plane thermal conductivity of 1.8 W m^-1 K^-1, showcasing significant anisotropic thermal conductivity. Meanwhile, these films demonstrated excellent thermal stability, mechanical performance, and flame retardancy. Furthermore, employing Foygel's theory elucidated the impact of filler arrangement on thermal conductivity mechanisms and the actual application of 5 G device chips and LED lamps emphasizing the potential of these thermally conductive films in thermal management applications. This investigation contributes valuable design concepts and foundations for the development of anisotropic thermally conductive composites suitable for electron thermal management.

Key words: Magnetic response, Boron nitride nanosheets, Orientation arrangement, Thermal conductivity, Flame retardancy