Structural Design of a Low-Dk, Low-CTE Negative Photoresist Polyimide with Water-Based Development Capability and Low-Temperature Curing Properties

To address the current challenge in advanced packaging technology where it is difficult to simultaneously achieve multiple outstanding properties in photosensitive polyimide (PSPI) structural designs. This work designed a low dielectric constant (Dk), low coefficient of thermal expansion (CTE) negative-photosensitive polyimide with water-based development capable of low-temperature curing. The method achieves low Dk (minimum ε < 3.0 at 10 GHz) and low CTE (minimum CTE as low as −3.23 ppm/K) by introducing a fluorinated rigid backbone structure into the polyamide ester (PAE, PSPI precursor) main chain. Simultaneously, photosensitive groups and water-soluble quaternary ammonium groups were incorporated into the side chains to enable high-resolution aqueous development (up to 4 μm). Quaternary ammonium salts degrade into tertiary ammonium during the imidization stage, which can further catalyze the low-temperature thermal imidization of PAE. Side chains degrade and vanish during imidization while preserving the polyimide backbone’s superior properties. This method achieves the synthesis of PSPI with multiple outstanding properties through sophisticated molecular structure design. This passage tackles the existing bottlenecks in PSPI performance stemming from structural limitations, aligns with the evolving requirements of cutting-edge packaging technologies, and showcases remarkable promise for future applications.