POLY(ESTER IMIDE)S AS HEAT-RESISTANT DIELECTRIC SUBSTRATES

摘要

Some commercially available polyimide (PI) films are known to possess good dimensionalrnstability against various thermal processes, which is based on their low linear coefficients ofrnthermal expansion (CTE). Therefore, they are used as dielectric substrates (base films) in flexiblernprinted circuit boards (FPC). However, the dimensional stability against water/moisturernabsorption is not always sufficient for the current PI systems. In the present work, we proposernpoly(ester imide)s (PEsIs) as a new type of the base film materials. The PEsI filmsrnsimultaneously achieved low CTE comparable to that of cupper foils, suppressed waterrnabsorption (WA), low linear coefficients of humidity expansion (CHE), very high glass transitionrntemperatures (Tg), sufficient film toughness. An increase in the content of the ester groupsrnincorporated in the PI main chains somewhat reduced the non-flammability. In order to solve thisrnproblem, we prepared novel phosphorus-containing monomers. Copolymerization using the Pcontainingrnmonomers at a minor content drastically improved the non-flammability whilernmaintaining the excellent combined properties. Recently, easily foldable low-stiffness FPCs arerndesired in some cases. The use of lower-modulus base films can be an effective strategy for thisrnpurpose. The present work also discusses an approach addressed to lower modulus withoutrnsacrificing excellent combined properties.