Preparation and Properties of Polyisoimides as a Highly Dimensionally Stable Polyimide Precursor with Low Dielectric Constant

Fluorinated polyimides (PIs) with low dielectric constant and high dimensional stability have been developed using polyisoimides (PIIs) as a polyimide precursor. The PIIs were prepared by the ring-opening polyaddition of the dianhydrides pyromellitic dianhydride, biphenyltetracarboxylic dianhydride and 4, 4′-hexafluoropropylidenedi(phthalic anhydride) with the diamines 2, 2′-dimethylbenzidine and 2, 2′-bis(trifluoromethyl)benzidine, followed by treatment with trifluoroacetic anhydride/triethylamine or dicyclohexylcarbodiimide in N;N-dimethylacetamide. The PIIs were soluble in a wide range of solvents including dipolar aprotic solvents, cyclohexanone and tetrahydrofuran at room temperature, and easy to convert to corresponding PIs by high thermal treatment. The resulting PIs showed low dielectric constants of less than 3 at 1 MHz as well as low CTEs. Furthermore, during the isomerization reaction, migration of copper in the PI film was hardly observed.