UBM-(Under-Bump-Metallurgy)-Systems

IMEConfidential&ProprietaryPage1UBM(UnderBumpMetallurgy)Systems1.DefinitionofUBM2.RoleofUBM3.UBMtypesandcharacterization4.CaseStudy5.SummaryIMEConfidential&ProprietaryPage2WhyUBMStudyisrequired?IMEConfidential&ProprietaryPage3•Materials•DepositionUBMEvolutionIMEConfidential&ProprietaryPage4UBMMetalsLayerFunctionMetalAdhesion,DiffusionBarrierCr,Ti,Ti-W,ZnSolderWettingCu,Ni,Ni-VOxidationProtectionAu,PdIMEConfidential&ProprietaryPage5C-4UBMStructureAuCuCrC-4:controlledcollapsechipconnectionIMEConfidential&ProprietaryPage6•C4means“Controlled-CollapsedChipCarrier”•FlipChipwasdevelopedbyIBMin1963.•FlipChipreplacesthewiresandleadsofconventionalpackageswithmoundsofsolder.•C4wasbasedonshadow-maskevaporationofsolder.C4TechnologySource:IBM2002IMEConfidential&ProprietaryPage7UBMMetallurgySetsOriginalC-4Cr/Cu/AuAlternatives-A(Copper-Wetting)Ti/Cu/AuTi/CuAlternatives-B(Nickel-Wetting)Ti/Ni/PdTi/NiZn/Ni/AuAl/Ni-V/CuAuCuCrIMEConfidential&ProprietaryPage8UBMCr/Cr:Cu/Cu/(Au)TiW/Cu/(Au)/Cumini-bumpAl/NiV/CuENIGMethodEvaporatedSputter+ElectroplatingsputterNi/AuElectrolessPlatingAdhesionLayerCr1)Ti:W2)Cr:CuAlNiSolderDiffusionBarrierCr:CuCustud/mini-bumpNiNiSolderWettableLayerCuCuCuAuOxidationPreventionAuAuCuAuSuitabilityfor63Sn-37PbNoPoorYesYesUsewithProbedWafersNoNoYesMixedCompanyMassproductioninIBM&MotorolaAT&T,Casio,Citizen,Motorola,AptosDelco,FCT,Lucent,PacTechICInterconnectUBMMetallurgySetsENIG:ElectrolessNickel/ImmersionGoldIMEConfidential&ProprietaryPage9Cr/Cr:Cu/Cu/Au•PhasedCr:CulayerisanextremelyreliablesolderdiffusionbarrierforhighleadsoldersbutisnotsuitableforeutecticPb-Snsolders.•Cr/Cr:Cu/CustructureisahigherstressthinfilmthanotherUBMs.ThereforeitisnotrecommendedtousethisUBMonprobedwafers.•UBMadhereswelltotheICmetallizationandpassivation,protectingtheunderlyingbondpad.•Field-provenreliabilityIMEConfidential&ProprietaryPage10SnPbSnAgCr/CrCu/Cu(1500Å/3000Å/8000Å)Source:KAISTIMEConfidential&ProprietaryPage11IMCSpalling–Cr/CrCu/CuSource:KAISTIMEConfidential&ProprietaryPage12研究了不同回流次数下SnAg/Cu的界面反应和孔洞形成机理,及其对凸点连接可靠性的影响.回流过程中SnAg与Cu之间Cu6Sn5相的生长与奥氏熟化过程相似.SnAg/Cu6Sn5界面中孔洞形成的主要原因是相转变过程中发生的体积缩减.凸点的剪切强度随着回流次数的增多而增大,且多次回流后SnAg/Cu界面仍然结合牢固.Cu6Sn5/Cu平直界面中形成的孔洞对凸点的长期可靠性构成威胁.Cu3Sn相产生体积变化，对可靠性有较大影响。IMEConfidential&ProprietaryPage13TiW/Cu/Au/Cumini-bump•sputteringofTiW/Cu/AupluselectroplatingofCumini-bump(5~25㎛).•UBMadherestothewaferpassivationaswellastothebondpad.•Ti:Wisacomparativelyhighstressthinfilmwhichcanreducereliability.•Themini-bumpgeneratesalargeamountofstresstowafer.•SiliconCratering:•VariationsoftheCr/Cr:Cu/CuUBMsystems(IBM/Unitive)haveshownpoorresultswitheutecticsolder.•ThisUBMiscompatiblewitheutecticPb-Snsolder.However,excessivebrittleintermetalliclayerformationcancausereliabilityproblemIMEConfidential&ProprietaryPage14TiW/Cu/electroplatedCu(2000Å/3000Å/5µm)SnPbSnAgSource:KAISTIMEConfidential&ProprietaryPage15可控的冷却速率可控制液态温度以上时间，快速冷却可以细化晶粒，提高强度，防止偏析，增强可靠性，避免Ag3Sn和Cu6Sn5等树枝状结晶的形成IMEConfidential&ProprietaryPage16Al/NiV/Cu•Field-provenUBM.Canwithstandover10reflowcycles.•Canbeusedonprobedwaferswithoutfearofaffectingreliability.•AlformsastrongadhesiontothewaferpassivationaswellastotheAlbondingpads•Nilayerservestwofunctions:itisanexcellentsolderdiffusionbarrier,especiallyfor63Sn/PbsoldersanditprovidesasolderwettablesurfaceafterCuisconsumed.•CuisusedtokeeptheNifromoxidizingand,unliketheplatedmini-bumpprocess,isnotneededtoallowthesolderbumptoadheretotheUBM.IMEConfidential&ProprietaryPage17NiV/Cu(2000Å/8000Å)SnPbSnAgSource:KAISTIMEConfidential&ProprietaryPage18NoIMCSpallingNiVlayerstillremainedafterheat-treatment.Source:KAISTIMEConfidential&ProprietaryPage19Sn/3.5Ag,60µmSizeBumpFractureAnalysiswithUBMsSource:KAISTIMEConfidential&ProprietaryPage20ElectrolessNi/Au•verysimpleduetomasklessprocess.•60%projectedcostofscreenprinting.•Nionlyadherestothebondpad,nottothepassivation.•ExceptfortheAlbondpads,allexposedmetalshouldbepassivated.•Thewafersshouldnotbebackgroundandshouldalsobefreeofcontaminantsbecausetheintroductionofforeignmaterialcansignificantlyeffecttheyieldonanentirebatch.•TheeutecticPb-Snsolderhasbeenfoundtobecompatiblewiththisprocess.IMEConfidential&ProprietaryPage21GrowthofIMCStructure(Solderetched)eNiAu/SnPbsolderSource:KAISTIMEConfidential&ProprietaryPage22eNi/AuwithPb-freesoldersSource:KAISTIMEConfidential&ProprietaryPage23InterfaicalMicrostructure;IMCSource:KAISTIMEConfidential&ProprietaryPage24Kirkendallvoids(250°C,16minreflow)Origin1.SndiffusionintoPrichNilayer2.Differenceindiffusionrateofeachelement(Sn,Ni,P)SndiffusionNiorPdiffusionExpectedresults1.Voidscanbebrittlefailuresites2.DegradationofsolderjointreliabilityElectrolessNiPrichNilayerIMCIMEConfidential&ProprietaryPage25ComparisonofUBMconsumptionSource:KAISTIMEConfidential&ProprietaryPage26BumpingTechnologyComparisonACF:AnisotropicConductiveFilmIMEConfidential&ProprietaryPage27Source:TechSearchUBMsystemsintheMarketCompanyUBMSolderBumpingMethodApackCr/CuScreenPrintingAptosTi-W/CuElectroplatingASEAl/NiV/CuCasioTi/Cu/NiChipbondTiW/CuCitizenCr/CuEMMicroelectr