2015 Volume 28 Issue 6 Pages 747-754
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 CO2 and the CO2-tertiaryamine zwitterions in polyimide precursor solutions to create 1-3 μm pores of >70% porosity. However, the film size was limited to 30 × 30 mm2. A larger film (70 × 150 mm2) 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 mm2 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.