ABSTRACT
Polyimides(Pis)andtheirhybridshavebeenwidelyusedinmanyelectronicapplications.AromaticPis[I,2]notonlypossessoutstandingthermalstability,but alsootherkeypropertiessuchashighmodulus,highmechanicalstrength,lowdielectricconstantandgoodopticalpropertiesandchemicalresistance.Thesehave beenused[3,41fordielectricinterlayerinsemiconductordevices,aswirecoating materialsandassubstratesforflexibleprintedcircuits.Themechanicalproperties ofPisareimprovedbyinclusionofsilicainthematrix.ThePI-silicacomposites [5-7]developedbythesol-gelprocess,therefore,havewidelybeenusedinelectronicapplications.Pisaregenerallyproduced[1-4]byacondensationreaction betweendianhydridesanddiaminesinaproticpolarsolventssuchasN,Ndimethylacetamide(DMAc),N-methyl-2-pyrrolidone,dimethylsulfoxide,orN,Ndimethylformamideformingpoly(amicacid)(PAA),asolubleprecursorofPI. Tetraethoxysilane(TEOS)canalsobeusedtodevelopasilicanetworkthrough thesol-gelprocessinthePAAsolution.ThePAAfilmsarecastbythesolvent
elutiontechniqueandarecyclo-imidizedtoobtainthefinalproduct.Thesolvents usedinthePAAformationgenerallyhaveahighdipolemomentandhighboiling temperature.TheinteractionbetweenthesolventandthePIpre-polymertendsto plasticisethefilmduringimidizationwhichmayhelpthecuringprocess.While theuseofthermalenergyismorecommon,microwaveenergy[8-10]hasalso beenusedlatelytocurePIcomposites,laminatesandcoatings.Themechanismof energytransferhereisbyelectricdipolarcouplingoftheradiationtopermanent dipolesinthepolymerratherthanbythermalconductivityasintheconventional thermalprocess.Themaximumimidizationachievedbymicrowaveprocessing [9],however,isonlyabout50%atthefullpowerlevel.Thermalcuringmethods, therefore,generallyareconsideredasmoreeffective.
