Supercritical carbon dioxide foaming for ultra-low dielectric loss perfluorinated foam

Abstract

Microelectronic is developing towards high frequency (GHz) and high speed (Gpbs), putting forward high requirements for low dielectric materials. The most efficient method for fabricating low dielectric materials is the incorporation of air into matrix via supercritical CO2 foaming. Herein, a low dielectric thermoplastic perfluorinated polymer is selected to be the matrix and another low dielectric perfluorinated polymer which is capable to form in-situ nanofibrils is selected to regulate the matrix viscoelasticity. Supercritical CO2 foaming method is then applied to introduce a large amount of low dielectric air into nanofibrill modified perfluorinated polymer. Owing to supercritical CO2 as a residue-free foaming agent (residue impurities in matrix originated from foaming agent would increase dielectric loss significantly at GHz) and its strong interaction with perfluorinated polymer (ensure large expansion ratio of the obtained foams to introduce a large amount of low dielectric air in matrix), the lowest dielectric loss of 0.00015 (among the existing polymeric materials) is then obtained by supercritical CO2 foaming of in-situ nanofibril modified perfluorinated polymer. Furthermore, the hydrophobic and oilphobic properties of the perfluorinated polymer were enhanced by supercritical CO2 foaming to form a cellular structure; simultaneously, the corrosion resistance to strong alkali and V0 flame retarding properties of the ultra-low dielectric foam were maintained resulted from the perfluorinated cell walls. Therefore, such superior comprehensive performance of this ultra-low dielectric perfluorinated foam made from supercritical CO2 foaming enables it the best alternative for the next-generation high-frequency (GHz to THz) and high-speed (sub Tbps) signal transmission substrate in electronics.