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Lateral Patterning of Porous Polyimide Film by Exposure to High-Pressure CO2 and UV Light with Photomask

Porous polyimide film is a promising substrate for high-frequency data transmission owing to its low dielectric constant and low attenuation of signal. In this study, lateral patterning of porous polyimide, consisting of porous and non-porous areas, was performed selectively using a photomask via a two-step UV irradiation method. The first UV irradiation polymerized the tertiary amine monomer that participates in the selective formation of pores with the photomask. The second UV irradiation was administered after the product was exposed to high-pressure CO2. The porous structure was observed over the masked area; none or few pores existed over the exposed area. The optimal lateral pattern rate of the porous structure is 21% with an expansion ratio of 1.26 corresponding to porosity. Moreover, the mean diameter of isolated pores was measured at 2.7 μm. The technique used is a promising approach to draw electrical circuits arbitrarily while retaining the mechanical strength and electrical insulation.