Balancing photosensitivity and visible-light absorption in intrinsically black photosensitive polyimide: synthesis and metal patterning
The escalating power density of electronic devices necessitates effective visible-light shielding in advanced packaging to ensure circuit security and long-term reliability. Photosensitive polyimides (PSPI) serve dual roles as photodefinable dielectrics and structural layers, but intrinsically black PSPI (B-PSPI) suffer from competitive ultraviolet (UV) absorption between chromophores and photosensitive moieties, limiting co-optimization of deep visible-light blocking and lithographic resolution. Here, we report a main-/side-chain spatial decoupling strategy to synthesize a novel B-PSPI. By polymerizing pyromellitic dianhydride with a main-chain coloring monomer (4,4'-diaminodiphenylamine) and a side-chain photosensitive monomer (1,4-dihydropyridine-functionalized diamine), the monomer stoichiometric ratio is precisely engineered. This design spatially isolates functional groups and enhances charge transfer, yielding exceptional visible-light shielding (CIE L* index of 21.39, cut-off wavelength ≈ 555 nm) with good lithographic sensitivity. UV exposure triggers in situ generation of coordination sites from photosensitive groups, anchoring active metal species for electroless copper plating. This enables direct additive fabrication of fine copper lines (40/80 μm line width/spacing) with robust Cu/B-PSPI interfacial adhesion of 16.6 MPa. This work provides a robust molecular design paradigm for B-PSPI, integrating superior optical shielding and surface metallization for high-density interconnect applications.