Molecular Design of Fluorine-Free Bio-Based Positive-Type Photosensitive Polyimides with Low Dielectric Properties

Photosensitive polyimides (PSPIs) are widely used as dielectric and passivation materials in semiconductor packaging owing to their excellent thermal stability, mechanical strength, chemical resistance, and photopatternability. However, most commercial PSPIs are derived from petroleum-based feedstocks and fluorinated monomers, raising concerns regarding sustainability and environmental impact. In this study, a series of fluorine-free bio-based polyimides were synthesized from an isosorbide-derived dianhydride and structurally diverse aromatic diamines, including APAB and ester-linked diamines bearing phenyl, norbornyl, and benzene pendant groups. The polymers were further copolymerized with 1,4-phenylene bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) (TAHQ) and 4,4′-biphthalic anhydride (s-BPDA) to tailor their molecular structures and properties. The effects of diamine and dianhydride structures on the dielectric, thermal, and dimensional properties of the resulting polyimides were systematically investigated. The incorporation of bulky pendant groups increased free volume and reduced dielectric polarization, resulting in lower dielectric constant and dissipation factor while maintaining excellent thermal performance. The optimized polyimide was subsequently combined with a diazonaphthoquinone (DNQ) photoactive compound to develop a bio-based positive-type PSPI system. The influences of DNQ structure and lithographic processing conditions on dissolution behavior and photolithographic performance were further evaluated. This work demonstrates a sustainable molecular design strategy for developing fluorine-free bio-based positive-type PSPIs with balanced dielectric, thermal, and photolithographic properties for advanced semiconductor packaging applications.