A low dielectric constant photosensitive polyimide structure design for high-resolution water-based development

To address the current limitation in advanced packaging where water-developable photosensitive polyimides (PSPI) exhibit high dielectric constants due to polar groups (e.g., hydroxyl or carboxyl groups), a novel structural design approach for water-developable PSPI based on side-chain polyamide esters has been developed. This innovation successfully resolves the issue of elevated dielectric constants in existing water-developable PSPI formulations. This method enables aqueous development through the utilisation of tertiary ammonium groups in the side chains, while the side chains can be completely removed during the imidisation process without affecting the dielectric properties of the polyimide backbone. Based on this method, fluorinated groups, bulky side groups, and alicyclic rings were introduced into the molecular backbone to synthesise a series of structurally diverse PSPI polymers. All these PSPIs feature low dielectric constants (with the lowest ɛ < 2.5 at 10 GHz) while achieving photolithographic resolution down to 2 μm. This represents a major breakthrough in the field of water-developable low-dielectric-constant photoresist polyimides, meeting the demands of advanced packaging technology development and demonstrating excellent application potential.