Fabrication of nanoporous polyimide of low dielectric constant

Polyimide is a choice of material widely used in electronic packaging due to its high thermal and mechanical stability and low thermal expansion coefficient and dielectric constant. Two porous polyimides of structure shown in the following figure were successfully synthesised. The reaction scheme involve polycondensation of 3,3\´,4,4\´-biphenyltetracarboxylic dianhydride with 4",4\´\´\´-(hexafluoroisopropyllidene)-bis(4-phenoxyaniline) and 4,4\´-(4,4\´-isopropylidenediphenyl-1,1\´-diyldioxy) dianiline followed by thermal curing of the intermediate polyamic acid. This treatment afforded a high molecular mass polyimide of tough and thermally stable polymer. Nanofoam polyimide films were fabricated by means of sol-gel technique to give a homogeneously dispersed nano-sized voids in range 100-400 nm. Both materials showed an ultra-low dielectric constant of 2.76 and 2.84 respectively. Comparison of the treated and non-treated polyimide films showed that the gain in low dielectric constant is achieved at a considerable expanse of mechanical properties.