Electrically Insulating Heat Spreaders for High-Power Electronics: Comparing a Hexagonal Boron Nitride Composite to a Graphene Laminate

Paper in proceeding, 2026

The increasing power density and miniaturization of certain electronic devices demand lightweight heat spreaders that offer high thermal conductivity while maintaining electrical insulation. This study compares two electrically insulating heat-spreading solutions: (i) a highly filled hexagonal boron nitride (hBN)-polymer composite film serving as an intrinsically insulating heat spreader, and (ii) a graphene-assembled film combined with a Kapton insulating layer. Custom-fabricated hBN films (∼200 μm thick) with strong in-plane alignment and ∼93 wt% hBN content were characterized using Scanning Electron Microscopy (SEM), thermo-gravimetric analysis (TGA), and electrical breakdown voltage measurements. Both heat-spreader configurations were experimentally evaluated under identical thermal loading using a customized thermal test rig, complemented by numerical modeling to assess the influence of lateral dimensions. Experimental results show that for larger lateral sizes (40 mm diameter), the graphene/Kapton configuration achieves lower heater temperatures and reduced thermal resistance due to graphene's high in-plane thermal conductivity. However, modeling indicates that as the heat-spreader diameter decreases, the performance of the graphene/Kapton configuration degrades more rapidly, whereas the hBN-based film becomes comparatively more effective due to its superior through-plane heat-transfer capability. Electrical testing further confirms that the hBN-based heat spreader shows significantly higher partial discharge (PD) and surface flashover voltages. These findings underscore the critical role of anisotropic thermal transport and lateral size in the design of electrically insulating heat spreaders for advanced power-electronics thermal management.