Robust Flexible Microwave Dielectric Film with High Thermal Conductivity and Ultralow Loss

Dielectric films with high thermal conductivity and excellent fatigue‐resistant flexibility are crucial for high‐frequency electronic applications, particularly for wearable electronics, soft robots, and foldable devices. Recently, extensive efforts to enhance the thermal conductivity of dielectric materials have driven substantial advancements. However, highly thermally conductive composites typically exhibit rigidity, brittleness and high dielectric loss, primarily due to the heavy incorporation of rigid thermally conductive fillers. To mitigate these undesirable effects of rigid fillers, flexible dielectric films featuring a nature‐inspired soft‐hard segmented structure are fabricated, achieving an in‐plane thermal conductivity of 18 W m −1 K −1 and an ultralow dielectric loss of 0.008 at 10 GHz. The high loading of oriented boron nitride (BN) enhances thermal conductivity and reduces dielectric loss, and the segmented structure imparts remarkable flexibility, sustaining over 1000 bending cycles without degradation. This biomimetic soft‐hard (polyacrylate‐BN) segmented architecture effectively balances three key performance metrics: high thermal conductivity, low elastic modulus, and low‐loss dielectric materials—overcoming a longstanding challenge in dielectric material design. Overall, this robust flexible microwave dielectric film is well suited for large‐scale production and holds significant application potential in advanced electronic packaging, including microwave devices, flexible electronics, sensors, and robotics.