Ultralow-k Dielectrics Made by Supercritical Foaming of Thin Polymer Films

Isawa

Mizoguchi

2017

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.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Isawa

Mizoguchi

2017

“…The preparation of a porous PI film has been continuously studied by several researchers. Some of the studies have succeeded in creating ultra-low k porous material in which the relative dielectric constant is less than two [3][4][5][6][7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

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

Mizoguchi

Ito

2016

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.

“…Voids were successfully formed in the PI, although the porosity was limited by the small number of pores. Another approach to forming pores involves the physical foaming technique, wherein CO 2 gas dissolved in a polymer matrix is thermally phase-separated to induce bubble nucleation in the glassy and rubbery state of the polymer [8,9]. The dielectric constant achieved using this method is 1.77, which is known as the ultralow-k level [9].…”

Section: Introductionmentioning

confidence: 99%

“…Another approach to forming pores involves the physical foaming technique, wherein CO 2 gas dissolved in a polymer matrix is thermally phase-separated to induce bubble nucleation in the glassy and rubbery state of the polymer [8,9]. The dielectric constant achieved using this method is 1.77, which is known as the ultralow-k level [9]. A supercritical fluid-assisted extraction technique has been applied to remove mesoscale domains in a PI matrix, whereas the remaining domains are allowed to become voids [10].…”

Section: Introductionmentioning

confidence: 99%

Development of a High-Intensity UV Exposure Apparatus under a High-Pressure CO2 Gas Atmosphere to Manufacture Large-Area Porous Ultralow-k Polyimide Substrates for Flexible Print Circuits

Ito

2015

Ultralow-k (dielectric constant) films are promising substrates for next-generation flexible print circuits. Introducing numerous pores into the film can effectively reduce the substrate's dielectric constant because the relative dielectric constant of air is smaller than that of any polymer substrate. We recently developed a short-cycle time process employing high-pressure CO 2 and the CO 2 -tertiaryamine zwitterions in polyimide precursor solutions to create 1-3 μm pores of >70% porosity. However, the film size was limited to 30 × 30 mm 2 . A larger film (70 × 150 mm 2 ) was required to measure the signal attenuation of an electrical circuit on a porous PI film as a next-generation flexible cable. In this paper, the developed process was scaled up to obtain 10-fold-larger ultralow-k films of porous polyimide. The process involved a high-intensity UV lamp, thick-quartz window and hydraulically movable sealing plate and produces 70 × 150 mm 2 films, which was a suitable size for high-speed data communication transmission tests. The preliminary results of building up a printed circuit on the porous substrate and signal attenuation measurements at 20 GHz demonstrated that the low-k porous PI substrate reduced the signal attenuation compared to a non-porous substrate with the same cross-sectional line area.