Preparation and Properties of High Thermal Conductivity Carbon Fiber Composites Based on Flow Shear/Calendering Coupling Orientation Method

Carbon‐fiber (CF)‐oriented thermal interface materials (TIMs) can effectively improve interfacial heat conduction in high‐power‐density chips, but existing orientation methods usually show low efficiency and difficulty in balancing high thermal conductivity (κ) with mechanical adaptability. Here, a flow shear/calendering coupling secondary orientation method was proposed using polydimethylsiloxane (PDMS) as the matrix, pitch‐based CFs as the main filler, and multisized spherical alumina (Al 2 O 3 ) as auxiliary fillers. Al 2 O 3 particles were used to bridge adjacent CFs and fill polymer‐rich gaps, while flow shear and calendering enabled more than 80% of CFs to orient vertically. With a 10 μm:2 μm Al 2 O 3 mass ratio of 6:4 and 13 wt% CFs, the through‐plane κ measured by the heat flow method reached 25.6 W/(m·K), 29.3% higher than the primary‐oriented sample and 666.5% higher than the randomly oriented sample. The optimized TIM also showed good flexibility and compressibility, with a compression ratio of 16.9% under 20 psi. In light‐emitting diode heat‐dissipation tests, the oriented CFs pad stabilized the chip temperature at 56.8°C, outperforming randomly oriented and commercial pads. This work provides a practical route for developing high‐performance TIMs.