Controlling the Pore Structure of Polyimide Films Prepared by Exposure to High-Pressure CO₂ and UV Light

Abstract

Porous polyimide is a promising low-permittivity material for reducing the attenuation of high-frequency signals. Previously, the suitability of porous polyimide films for flexible printed circuits was tested by subjecting them to cover-layering and copper plating. These treatments resulted in pore collapse and infiltration, respectively, indicating the necessity of using closed-pore films. Herein, closed-pore porous polyimide films were prepared at various CO 2 gas pressures, tertiary amine methacrylate monomer concentrations, and pre-baking times, revealing the key role of pre-baking time in maximizing porosity while preserving closed pores. In contrast to our previous study, the formation of closed pores was explained by a novel mechanism featuring CO 2 bubble nucleation as a key step.

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

“…Polyimide precursor was same as previous study [8]. Poly(amic acid) (PAA) solution was prepared by polymerization of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether in N,N-dimethyl acetamide at 80 °C under nitrogen, with 15 wt% solid content .…”

“…This decrease effectively lessens the dielectric loss of high-frequency signal in the metal line on the porous polyimide substrate. The dielectric constant reduction has been investigated by several researchers, as summarized in prior studies [1,2] and reviews [3,4] and in our previous articles [5][6][7][8].…”

“…The aqueous solution of copper plating infiltrated into the porous structure as the pores were partially interconnected. To produce isolated pores, solvent concentration was tuned [8]. However, the porosity of the resulting film was lower than that with interconnected pores.…”