SOS Wafer Cu Pillar Bumping Process Development for Flip Chip Package Application .pdf

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1、SOSWaferCuPillarBumpingProcessDevelopmentforFlipChipPackageApplicationJohn,ZhiyuanYangPeregrineSemiconductor9380CarrollParkDrive,SanDiego,CA92121,USAjyang@psemi.comAbstractI/OMetalPadCupillarbumpingprocesshasbeendevelopedonSOSGlassSealing(SilicononSapphire)waferforflipchippackageapplicationSa

2、pphirewaferSapphirewhileintheinitialpackagingexperimentopenfailurehasbeenfound.Voidinginbumppadmetalhasbeenfoundinpackagefailureanalysis.ThecracksinitiatedfromtheBCBlayervoidinghavealsobeencaptured.Furtherinvestigationhasconfirmedthatthesurfaceroughnessofbumppadmetaliscloselyrelatedtothisfail

3、ure.ThevoidingwasformedforDepositandpatternalayerofBCBthatthebumppadmetalwasetchedawaybyplatingsolventUBMinbumpingprocess.Solutionsonprocessandbumpmetalstructuredesignhavebeendiscussedandpresentedwithevaluationexperimentresultsinthispaper.DepositUBM(UnderBumpMetallization)IntroductionTheCupil

4、larbumpingforSOSwaferisbasedonelectricalplatingprocess.(figure2).Sapphirewaferisre-passivatedbyBCBcoatingthenTi/CuisspatteredonasUBM(underbumpmetallization)aswellastheseedlayerforelectricalplating.Afterpatternedbythickphotoresister,theDepositandpatternalayerofphoto-resistwaferisplacedinelectr

5、icalplatingprocessforthefabricationofCupillarandSnAgsoldercapsection.Cuisfirstplatedandcontrolledtotheheightcloseto50umthenfollowedbyathinlayerofNiplatingthenfilledupwithSnAgsolderplating.Afterthephotoresiststrippingthewaferwillgothroughthereflowforsoldercapformation,thenfollowedbyCupillarand

6、LeadfreesolderplatingtheprocessofUBMmetalstrippingwithchemicaletching[1].ThisCupillarbumpingprocesscanalsobeusedforsolderbumpingbychangingtheheightofCupillarfrom50umtoabout10umandletthisshortpillarfunctionasUBMmetal.Therestsectionwillbefilledwithplatedsolder.Afterreflowsolderbumpingcanbeobtai

7、ned.TheinitialpackagingexperimentwascarriedoutbasedReflowandUBMmetalstriponflipchipontwolayerBTsubstratepackage.Fig2.CupillarbumpingprocessflowInpackagereliabilityevaluationtestfortheflipchipon2layerBTsubstratepackage,someopenfailureshavehapp