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1、Chapter10NanoconductiveAdhesivesDaoqiangDanielLu(*ü),YiGraceLi,andC.-P.Wong10.1IntroductionElectricallyconductiveadhesives(ECAs)arecompositesofpolymericmatricesandelectricallyconductivefillers.Polymericmatriceshaveexcellentdielectricpropertiesandthusaree
2、lectricalinsulators.Theconductivefillersprovidetheelectricalpropertiesandthepolymericmatrixprovidesmechanicalproperties.Therefore,electricalandmechanicalpropertiesareprovidedbydifferentcomponents,whichisdifferentfrommetallicsoldersthatprovideboththeelect
3、ricalandmechanicalproperties.ECAshavebeenwithusforsometime.Metal-filledthermosetpolymerswerefirstpatentedasECAsinthe1950s[13].Recently,ECAmaterialshavebeenidentifiedasoneofthemajoralternativesforlead-containingsoldersformicroelectronicpackagingapplica-ti
4、ons.Therearetwotypesofconductiveadhesives:isotropicallyconductiveadhesives(ICAs)andanisotropicallyconductiveadhesives/films(ACAs/ACFs).ICAs,alsoknownaspolymersolder,areconductiveinalldirections.Theconductivefillersprovidethecompositewithelectricalconduct
5、ivitythroughcon-tactbetweentheconductiveparticles.Withincreasingfillerconcentrations,theelectricalpropertiesofanICAtransformitfromaninsulatortoaconductor.PercolationtheoryhasbeenusedtoexplaintheelectricalpropertiesofICAcom-posites.Atlowfillerconcentratio
6、ns,theresistivitiesofICAsdecreasegraduallywithincreasingfillerconcentration.However,theresistivitydropsdramaticallyaboveacriticalfillerconcentrationVcalledthepercolationthreshold(Fig.10.1).cItisbelievedthatatthisconcentration,alltheconductiveparticlescon
7、tacteachotherandformathree-dimensionalnetwork.Theresistivitydecreasesonlyslightlywithfurtherincreasesinthefillerconcentrations[46].Toachieveconductivity,thevolumefractionofconductivefillerinanICAmustbeequaltoorslightlyhigherthanthecriticalvolumefraction.
8、Similartosolders,ICAsprovidethedualfunc-tionsofelectricalconnectionandmechanicalbondinaninterconnectionjoint.InanICAjoint(Fig.10.2),thepolymerresinprovidesmechanicalstabilityandtheD.D.LuHenkelLoctite(China)Co.,Ltd,90Zhujia
