Photosensitive polyimide-precursor based on polyisoimide: dimensionally stable polyimide with a low dielectric constant

A positive-working photosensitive polyimide (PI) precursor based on fluorinated polyisoimide (FPII) and 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy) benzophenone (D5SB) as a photosensitive compound has been developed. FPII was prepared by ring-opening polyaddition of dianhydrides, pyromellitic dianhydride and biphenyltetracarboxylic dianhydride, with diamine, 2,2′-bis(trifluoromethyl benzidine and followed by treatment with trifluoroacetic anhydride-triethylamine in N-methyl-2-pytrolidinone. The FPII film showed a good solubility in a wide range of organic solvents. The dissolution behaviour of FPII containing 30 wt% of D5SB after exposure was studied and it was found that the difference of dissolution rate between the exposed and the unexposed parts was enough to get a positive pattern due to photochemical reaction of D5SB in the polymer film. The photosensitive fluorinated polyimide (FPI) precursor containing 30 wt% of D5SB showed a sensitivity of 250 mJ cm−2 and a contrast of 1.5 with 436 nm light, when it was developed with a mixture of 2.38% aqueous tetramethylammonium hydroxide solution and 2-propanol at room temperature. The FPI film cured up to 360°C had a low coefficient of thermal expansion of 10.8 ppm °C−1 and a low dielectric constant of 2.89.