Cover-layering a Porous Polyimide Flexible Print Circuit with a Porous Polyimide Layer

Abstract

Porous polyimide films are promising insulators for next generation electronic devices. Recently, we had developed a high-intensity UV exposure apparatus under a high-pressure CO 2 gas atmosphere for the production of porous polyimide films. In this study, the cover-layering process of a porous polyimide layer on two different types of flexible print circuits (FPCs) with insulation materials made of solid polyimide and porous polyimide was examined. Although a portion of the pores above and below the copper line of the FPC collapsed, a conformal porous polyimide layer could be formed on the FPC. Through-holes were formed on the porous polyimide film by a laser ablation technique. The surface of through-holes was electro-plated in a copper-plating solution bath. A portion of the pores on the film were filled with copper as the pores were inter-connected and the plating solution penetrated the pores. The results suggest that the pores should be isolated and firm for a cover-layering process with porous polyimide films for next-generation FPCs.

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

“…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 film was then used as cover layer for the micro strip line of the porous PI substrate. Moreover, copper plating was applied to the via hole of the porous PI film [7]. The aqueous solution of copper plating infiltrated into the porous structure as the pores were partially interconnected.…”

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

“…In our previous study, we tested the suitability of porous polyimide films for flexible printed circuits by subjecting them to cover-layering and copper plating [6]. The results showed that cover-layering induced the collapse of some pores, with copper plating leading to pore infiltration, indicating that such treatments require closed-pore films.…”

“…However, the increasing demand for mobile devices capable of faster data transfer requires the use of PI FPCs with low dielectric constants to decrease signal attenuation. Therefore, 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].…”