All‐Organic Hyper‐Crosslinked Polymer/Polyimide Composite Films with Ultralow High‐Frequency Dielectric Constant

The ever increasing demand for high-speed communication at high frequency promotes the rapid development of low-dielectric polymer films. Aromatic polyimide (PI) has been widely used as the main dielectrics in the flexible circuit board due to its excellent dielectric, mechanical, and thermal properties. Nevertheless, the dielectric constant of PI films at a high frequency range (several GHz) is relatively high and cannot satisfy the requirement of high-frequency communication. On this basis, a hyper-crosslinked polymer (HCP) and fabricated all-organic HCP/PI composite films through a physical blending method is synthesized. The porous structure of HCP is helpful to reduce the dielectric constant of PI matrix. The effects of HCP loadings on the dielectric, mechanical, and thermal properties of HCP/PI composite films are systematically investigated. The dielectric constants of the composite films can be reduced to 1.6-1.8 in the frequency range of 8.2-9.6 GHz when the HCP content reached 10 wt.%. The proposed method in this work is simple and effective to reduce the dielectric constant of PI and can be easily extended to other organic component-filled PI systems.