Manipulative pore-formation of polyimide film for tuning the dielectric property via breath figure method

Polyimide (PI) films have been extensively used in the field of microelectronic as insulating materials. With the rapid development of microelectronic devices towards miniaturization and large power, the development of low dielectric properties of PI materials has attracted more and more attention. In this study, the breath figure (BF) process was used to prepare single-layered and multi-layered microporous PI films, for obtaining the low dielectric properties. The BF porous structure of PI film was successfully constructed by two implementing strategies, i.e., solution casting for direct preparation of PI film and solvent treatment upon pre-shaped PI film for in-situ pore-formation. By changing solution concentration, environmental humidity and temperature, efficient manipulation of the pore morphology of the film both on the surface and in the bulk layer was achieved. Such multi-layered porous BF structure has been proved to significantly lower the dielectric constant of PI film, from 3.7 of non-porous film to 1.7 of porous film. In order to further expand the application range of BF microporous PI film, both ways of alkali treatment and thermal oxidation were taken for the cross-linking of the porous PI films, greatly improving the solvent resistance of the film. The original porous morphology was completely retained, ensuring that the low dielectric properties were not affected. This is the first report on the preparation of multi-layered microporous low dielectric PI films by BF process.