Hierarchical porous structure contained composite polyimide film with enhanced dielectric and water resistance properties for dielectric material

Enhancement of dielectric and water resistance properties of PI film were achieved through the introduction of hierarchical porous coating. [Display omitted] •A composite film based on PI and POSS was fabricated using self-assembly method.•Hierarchical porous structure was used as a coating for PI film in composite film.•The composite film exhibits low dielectric constant and water uptake.•Excellent durability of low dielectric constant under high humidity was shown.•The mechanical properties were maintained when other properties were optimized. Low-dielectric-constant materials are in great demands to satisfy the requirements in microelectronics. In this study, polyhedral oligomeric silsesquioxanes (POSS) contained hierarchical porous structure, which was prepared by the self-assembly of water droplets, was used as a coating for flat polyimide (PI) film. Evident declines were found in dielectric constant and water uptake upon the introduction of the hierarchical porous coating due to the existence of fluorine-containing groups, POSS and the hierarchical porous structure. In addition, almost undamaged mechanical properties were shown when the dielectric and water resistance properties were optimized because the hierarchical porous structure was used as a coating but not the bulk of the PI film. When the content of POSS varies from 10 % to 50 %, low dielectric constants of 2.42–2.75 and low water uptakes of 0.60 %– 0.67 %, with 22 %–27.63 % and 75.96 %–78.43 % of reductions were obtained, compared to 3.36 of dielectric constant and 2.80 % of water uptake for flat PI film. More importantly, the stability of dielectric properties in humid environment was verified by only 2.94 %–4.83 % of increase in dielectric constant after exposing to high humidity for more than 25 h, compared to 9.43 % of increase for flat PI film. The present study provides a versatile method for the preparation of low-dielectric-constant polymer materials with comprehansive properties.