Enhanced thermal transport of hexagonal boron nitride filled polymer composite by magnetic field-assisted alignment

High thermal conductivity, electrical insulating polymer composite has a wide range of applications in electronic packaging. We report the magnetic alignment of hexagonal boron nitride (hBN) in epoxy composite and the greatly enhanced thermal conductivities of the composites. Superparamagnetic iron oxide nanoparticles are used to modify the surface of hBN, making it responsive to the external magnetic field. The orientation of modified hBN can be controlled by applying an external magnetic field during the curing of epoxy resin. The thermal conductivity of 20 wt% vertically aligned hBN-epoxy composite is found to be 104 % higher than the randomly aligned counterpart. This dramatically enhanced thermal conductivity is theoretically studied by effective medium approximation. The linear coefficient of thermal expansion for 20 wt% vertically aligned hBN-epoxy along the alignment direction is as low as 28.7 ppm/K due to the magnetic alignment and anisotropic thermomechanical and mechanical properties of hBN. Moreover, the polymer composites still possess an excellent processibility. These results suggest the promising application of magnetically aligned hBN-based polymer composites in electronic packaging.