汽车电子系统中英文对照外文翻译文献

外文资料翻译汽车电子系统中英文对照外文翻译文献(文档含英文原文和中文翻译)TheChangingAutomotiveEnvironment:High-TemperatureElectronicsR.WayneJohnson,Fellow,IEEE,JohnL.Evans,PeterJacobsen,JamesR.(Rick)Thompson,andMarkChristopherAbstract—Theunderhoodautomotiveenvironmentisharshandcurrenttrendsintheautomotiveelectronicsindustrywillbepushingthetemperatureenvelopeforelectroniccomponents.Thedesiretoplaceenginecontrolunitsontheengineandtransmissioncontrolunitseitheronorinthetransmissionwillpushtheambienttemperatureabove125℃.However,extremecostpressures,increasingreliabilitydemands(10year/241350km)andthecostoffieldfailures(recalls,liability,customerloyalty)willmaketheshifttohighertemperaturesoccurincrementally.Thecoolestspotsonengineandinthetransmissionwillbeused.Theselargebodiesdoprovideconsiderableheatsinkingtoreducetemperatureriseduetopowerdissipationinthecontrolunit.Themajorityofneartermapplicationswillbeat150℃orlessandthesewillbeworstcasetemperatures,notnominal.ThetransitiontoX-by-wiretechnology,replacingmechanicalandhydraulicsystemswithelectromechanicalsystemswillrequiremorepowerelectronics.Integrationofpowertransistorsandsmartpowerdevicesintotheelectromechanicalactuatorwillrequirepowerdevicestooperateat175℃to200℃.Hybridelectricvehiclesandfuelcellvehicleswillalsodrivethedemandforhighertemperaturepowerelectronics.Inthecaseofhybridelectricandfuelcellvehicles,thehightemperaturewillbeduetopowerdissipation.Thealternatestohigh-temperaturedevicesarethermalmanagementsystemswhichaddweightandcost.Finally,thenumberofsensorsinvehiclesisincreasingasmoreelectricallycontrolledsystemsareadded.Manyofthesesensorsmustworkinhigh-temperatureenvironments.Theharshestapplicationsareexhaustgassensorsandcylinderpressureorcombustionsensors.High-temperatureelectronicsuseinautomotivesystemswillcontinuetogrow,butitwillbegradualascostandreliabilityissuesareaddressed.Thispaperexaminesthemotivationforhighertemperatureoperation,thepackaginglimitationsevenat125Cwithnewerpackagestylesandconcludeswithareviewofchallengesatboththesemiconductordeviceandpackaginglevelastemperaturespushbeyond125℃.IndexTerms—Automotive,extreme-environmentelectronics.I.INTRODUCTIONIN1977,theaverageautomobilecontained$110worthofelectronics[1].By2003theelectronicscontentwas$1510pervehicleandisexpectedtoreach$2285in2013[2].TheturningpointinautomotiveelectronicswasgovernmentTABLEIMAJORAUTOMOTIVEELECTRONICSYSTEMSTABLEIIAUTOMOTIVETEMPERATUREEXTREMES(DELPHIDELCOELECTRONICSYSTEMS)[3]regulationinthe1970smandatingemissionscontrolandfueleconomy.Thecomplexfuelcontrolrequiredcouldnotbeaccomplishedusingtraditionalmechanicalsystems.Thesegovernmentregulationscoupledwithincreasingsemiconductorcomputingpoweratdecreasingcosthaveledtoaneverincreasingarrayofautomotiveelectronics.AutomotiveelectronicscanbedividedintofivemajorcategoriesasshowninTableI.Theoperatingtemperatureoftheelectronicsisafunctionoflocation,powerdissipationbytheelectronics,andthethermaldesign.Theautomotiveelectronicsindustrydefineshigh-temperatureelectronicsaselectronicsoperatingabove125℃.However,theactualtemperatureforvariouselectronicsmountinglocationsvariesconsiderably.DelphiDelcoElectronicSystemsrecentlypublishedthetypicalcontinuousmaximumtemperaturesasreproducedinTableII[3].ThecorrespondingunderhoodtemperaturesareshowninFig.1.Theauthorsnotethattypicaljunctiontemperaturesforintegratedcircuitsare10℃to15℃higherthanambientorbaseplatetemperature,whilepowerdevicescanreach25℃higher.At-enginetemperaturesof125℃peakcanbemaintainedbyplacingtheelectronicsontheintakemanifold.Fig.1.Enginecompartmentthermalprofile(DelphiDelcoElectronicSystems)[3].TABLEIIITHEAUTOMOTIVEENVIRONMENT(GENERALMOTORSANDDELPHIDELCOELECTRONICSYSTEMS)[4]TABLEIVREQUIREDOPERATIONTEMPERATUREFORAUTOMOTIVEELECTRONICSYSTEMS(TOYOTAMOTORCORP.[5]TABLEVMECHATRONICMAXIMUMTEMPERATURERANGES(DAIMLERCHRYSLER,EATONCORPORATION,ANDAUBURNUNIVERSITY)[6]Fig.2.Automotivetemperaturesandrelatedsystems(DaimlerChrysler)[8].automotiveelectronicsystems[8].Fig.3showsanactualmeasuredtransmissiontemperatureprofileduringnormalandexcessivedrivingconditions[8].Powerbrakingisacommonlyusedtestconditionwherethebrakesareappliedandtheengineisrevvedwiththetransmissioningear.Asimilarreal-worldsituationwouldbeapplyingthrottlewiththeemergencybrakeapplied.Notethatwhenthetemperaturereached135℃,theovertemperaturelightcameonandatthepeaktemperatureof145℃,thetransmissionwasbeginningtosmellofburnttransmissionfluid.TABLEVI2002INTERNATIONALTECHNOLOGYROADMAPFORSEMICONDUCTORSAMBIENTOPERATINGTEMPERATURESFORHARSHENVIRONMENTS(AUTOMOTIVE)[9]The2002updatetotheInternationalTechnologyRoadmapforSemiconductors(ITRS)didnotreflecttheneedforhigheroperatingtemperaturesforcomplexintegratedcircuits,butdidrecognizeincreasingtemperaturerequirementsforpowerandlineardevicesasshowninTableVI[9].Highertemperaturepowerdevices(diodesandtransistors)willbeusedforthepowersectionofpowerconvertersandmotordrivesforelectromechanicalactuators.Highertemperaturelineardeviceswillbeusedforanalogcontrolofpowerconvertersandforamplificationandsomesignalprocessingofsensoroutputspriortotransmissiontothecontrolunits.Itshouldbenotedthatatthemaximumratedtemperatureforapowerdevice,thepowerhandlingcapabilityisderatedtozero.Thus,a200℃ratedpowertransistorina200℃environmentwouldhavezerocurrentcarryingcapability.Thus,theactualoperatingenvironmentsmustbelowerthanthemaximumrating.Inthe2003editionoftheITRS,themaximumjunctiontemperaturesidentifiedforharsh-environmentcomplexintegratedcircuitswasraisedto150℃through2018[9].Theambientoperatingtemperatureextremeforharsh-environmentcomplexintegratedcircuitswasdefinedas40℃to125℃through2009,increasingto40℃to150℃for2010andbeyond.Power/lineardeviceswerenotseparatelylistedin2003.TheITRSisconsistentwiththecurrentautomotivehigh-temperaturelimitations.DelphiDelcoElectronicSystemsofferstwoproductionenginecontrollers(oneonceramicandoneonthinlaminate)fordirectmountingontheengine.Thesecontrollersareratedforoperationoverthetemperaturerangeof40℃to125℃.TheECUmustbemountedonthecoolestspotontheengine.Thepackagingtechnologyisconsistentwith140℃operation,buttheECUislimitedbysemiconductorandcapacitortechnologiesto125℃.ThefutureprojectionsintheITRSarenotconsistentwiththedesiretoplacecontrollerson-engineorin-transmission.Itwillnotalwaysbepossibletousethecoolestlocationformountingcontrolunits.DelphiDelcoElectronicsSystemshasdevelopedanin-transmissioncontrollerforuseinanambienttemperatureof140℃[10]usingceramicsubstratetechnology.DaimlerChryslerisalsodesigninganin-transmissioncontrollerforusewithamaximumambienttemperatureof150℃(Figs.4and5)[11].II.MECHATRONICSMechatronics,ortheintegrationofelectricalandmechanicalsystemsoffersanumberofadvantagesinautomotiveassembly.Integrationoftheenginecontrollerwiththeengineallowspretestoftheengineasacompletesystempriortovehicleassembly.Likewisewiththeintegrationofthetransmissioncontrollerandthetransmission,pretestingandtuningtoaccountformachiningvariationscanbeperformedatthetransmissionfactorypriortoshipmenttotheautomobileassemblysite.Inaddition,mostofthewiresconnectingtoatransmissioncontrollerruntothesolenoidpackinsidethetransmission.Integrationofthecontrollerintothetransmissionreducesthewiringharnessrequirementsattheautomobileassemblylevel.Fig.4.PrototypeDaimlerChryslerceramictransmissioncontroller[11]Fig.5.DaimlerChryslerin-transmissionmodule[11].Thetrendinautomotivedesignistodistributecontrolwithnetworkcommunications.AstheindustrymovestomoreX-by-wiresystems,thistrendwillcontinue.Automotivefinalassemblyplantsassemblesubsystemsandcomponentssuppliedbynumerousvendorstobuildthevehicle.Completemechatronicsubsystemssimplifythedesign,integration,management,inventorycontrol,andassemblyofvehicles.Asdiscussedintheprevioussection,highertemperatureelectronicswillberequiredtomeetfuturemechatronicdesigns.III.PACKAGINGCHALLENGESAT125℃Trendsinelectronicspackaging,drivenbycomputerandportableproductsareresultinginpackageswhichwillnotmeetunderhoodautomotiverequirementsat125℃.Mostnotableareleadlessandareaarraypackagessuchassmallballgridarrays(BGAs)andquadflatpacksno-lead(QFNs).Fig.6showsthethermalcycletest40℃to125℃resultsfortwosizesofQFNfromtwosuppliers[12].Atypicalrequirementisfortheproducttosurvive2000–2500thermalcycleswith<1%failureforunderhoodapplications.SmallerI/OQFNshavebeenfoundtomeettherequirements.Fig.7presentsthethermalcycleresultsforBGAsofvariousbodysizes[13].ThediesizeintheBGAremainedconstant(8.6*8.6mm).Asthebodysizedecreasessodoesthereliability.Onlythe23-mmBGAmeetstherequirements.The15-mmBGAwiththe0.56-mm-thickBTsubstratenearlymeetstheminimumrequirements.However,theindustrytrendistousethinnerBTsubstrates(0.38mm)forBGApackages.OnesolutiontoincreasingthethermalcycleperformanceofsmallerBGAsistouseunderfill.CapillaryunderfillwasdispensedandcuredafterreflowassemblyoftheBGA.Fig.8showsaWeibullplotofthethermalcycledataforthe15-mmBGAswithfourdifferentunderfills.UnderfillUF1hadnofailuresafter5500cyclesandis,therefore,notplotted.Underfill,therefore,providesaviableapproachtomeetingunderhoodautomotiverequirementswithsmallerBGAs,butaddsprocesssteps,time,andcosttotheelectronicsassemblyprocess.Sinceportableandcomputerproductsdominatetheelectronicsmarket,thepackagesdevelopedfortheseapplicationsarereplacingtraditionalpackagessuchasQFPsfornewdevices.Theautomotiveelectronicsindustrywillhavetocontinuedevelopingassemblyapproachessuchasunderfilljusttousethesenewpackagesincurrentunderhoodapplications.IV.TECHNOLOGYCHALLENGESABOVE125℃Thetechnicalchallengesforhigh-temperatureautomotiveapplicationsareinterrelated,butcanbedividedintosemiconductors,passives,substrates,interconnections,andhousings/connectors.Industriessuchasoilwelllogginghavesuccessfullyfieldedhigh-temperatureelectronicsoperatingat200℃andabove.However,automotiveelectronicsarefurtherconstrainedbyhigh-volumeproduction,lowcost,andlong-termreliabilityrequirements.Thetypicaloperatinglifeforoilwellloggingelectronicsmayonlybe1000h,productionvolumesareintherangeof10sor100sand,whilecostisaconcern,itisnotadominantissue.Inthefollowingparagraphs,thetechnicalchallengesforhigh-temperatureautomotiveelectronicsarediscussed.Semiconductors:Themaximumratedambienttemperatureformostsiliconbasedintegratedcircuitsis85℃,whichissufficientforconsumer,portable,andcomputingproductapplications.Devicesformilitaryandautomotiveapplicationsaretypicallyratedto125℃.Afewintegratedcircuitsareratedto150℃,particularlyforpowersupplycontrollersandafewautomotiveapplications.Finally,manypowersemiconductordevicesarederatedtozeropowerhandlingcapabilityat200℃.Nelmsetal.andJohnsonetal.haveshownthatpowerinsulated-gatebipolartransistors(IGBTs)andmetal–oxide–semiconductorfield-effecttransistors(MOSFETs)canbeusedat200℃[14],[15].Theprimarylimitationsofthesepowertransistorsatthehighertemperaturesarethepackaging(theglasstransitiontemperatureofcommonmoldingcompoundsisinthe180℃to200℃range)andtheelectricalstressonthetransistorduringhardswitching.Anumberoffactorslimittheuseofsiliconathightemperatures.First,withabandgapof1.12eV,thesiliconp-njunctionbecomesintrinsicathightemperature(225℃to400℃dependingondopinglevels).Theintrinsiccarrierconcentrationisgivenby(1)Asthetemperatureincreases,theintrinsiccarrierconcentrationincreases.Whentheintrinsiccarrierconcentrationnearsthedopingconcentrationlevel,p-njunctionsbehaveasresistors,notdiodes,andtransistorslosetheirswitchingcharacteristics.Oneapproachusedinhigh-temperatureintegratedcircuitdesignistoincreasethedopinglevels,whichincreasesthetemperatureatwhichthedevicebecomesintrinsic.However,increasingthedopinglevelsdecreasesthedepletionwidths,resultinginhigherelectricfieldswithinthedevicethatcanleadtobreakdown.Asecondproblemistheincreaseinleakagecurrentthroughareverse-biasedp-njunctionwithincreasingtemperature.Reverse-biasedp-njunctionsarecommonlyusedinICdesigntoprovideisolationbetweendevices.Thesaturationcurrent(I,theidealreverse-biascurrentofthejunction)isproportionaltothesquareoftheintrinsiccarrierconcentrationwhereEgo=bandgapenergyatT=0KTheleakagecurrentapproximatelydoublesforeach10℃riseinjunctiontemperature.Increasedjunctionleakagecurrentsincreasepowerdissipationwithinthedeviceandcanleadtolatch-upoftheparasiticp-n-p-nstructureincomplimentarymetal–oxide–semiconductor(CMOS)devices.Epitaxial-CMOS(epi-CMOS)hasbeendevelopedtoimprovelatch-upresistanceasthedevicedimensionsaredecreasedduetoscalingandprovidesimprovedhigh-temperatureperformancecomparedtobulkCMOS.Silicon-on-insulator(SOI)technologyreplacesreverse-biasedp-njunctionswithinsulators,typicallySiO2,reducingtheleakagecurrentsandextendingtheoperatingrangeofsiliconabove200℃.Atpresent,SOIdevicesaremoreexpensivethanconventionalp-njunctionisolateddevices.ThisisinpartduetothelimiteduseofSOItechnology.Withthecontinuedscalingofdevicedimensions,SOIisbeingusedinsomehigh-performanceapplicationsandtheincreasingvolumemayhelptoeventuallylowerthecost.Otherdeviceperformanceissuesathighertemperaturesincludegatethresholdvoltageshifts,decreasednoisemargin,decreasedswitchingspeed,decreasedmobility,decreasedgain-bandwidthproduct,andincreasedamplifierinput–offsetvoltage[16].Leakagecurrentsalsoincreaseforinsulatorswithincreasingtemperature.Thisresultsinincreasedgateleakagecurrents,andincreasedleakageofchargestoredinmemorycells(dataloss).Fordynamicmemory,theincreasedleakagecurrentsrequirefasterrefreshrates.Fornonvolatilememory,theleakagelimitsthelifeofthestoreddata,aparticularissueforFLASHmemoryusedinmicrocontrollersandautomotiveelectronicsmodules.Beyondtheelectricalperformanceofthedevice,thedevicereliabilitymustalsobeconsidered.Electromigrationofthealuminummetallizationisamajorconcern.Electromigrationisthemovementofthemetalatomsduetotheirbombardmentbyelectrons(currentflow).Electromigrationresultsintheformationofhillocksandvoidsintheconductortraces.Themeantimetofailure(MTTF)forelectromigrationisrelatedtothecurrentdensity(J)andtemperature(T)asshownin(3)Theexactrateofelectromigrationandresultingtimetofailureisafunctionofthealuminummicrostructure.Additionofcoppertothealuminumincreaseselectromigrationresistance.Thetrendintheindustrytoreplacealuminumwithcopperwillimprovetheelectromigrationresistancebyuptothreeordersofmagnitude[17].Timedependentdielectricbreakdown(TDDB)isasecondreliabilityconcern.TimetofailureduetoTDDBdecreaseswithincreasingtemperature.Oxidedefects,includingpinholes,asperitiesattheSi–SiO2interfaceandlocalizedchangesinchemicalstructurethatreducethebarrierheightorincreasethechargetrappingarecommonsourcesofearlyfailure[18].Breakdowncanalsooccurduetoholetrapping(Fowler–Nordheimtunneling).TheholescancollectatweakspotsintheSi–SiO2interface,increasingtheelectricfieldlocallyandleadingtobreakdown[18].Thetemperaturedependenceoftime-to-breakdown(tBD)canbeexpressedas[18]ValuesreportedforEtbdvaryintheliteratureduetoitsdependenceontheoxidefieldandtheoxidequality.Furthermore,theactivationenergyincreaseswithbreakdowntime[18].Withproperhigh-temperaturedesign,junctionisolatedsiliconintegratedcircuitscanbeusedtojunctiontemperaturesof150℃to165℃,epi-CMOScanextendtherangeto225℃to250℃andSOIcanbeusedto250℃to280℃[16,pp.224].High-temperature,nonvolatilememoryremainsanissue.Fortemperaturesbeyondthelimitsofsilicon,siliconcarbidebasedsemiconductorsarebeingdeveloped.ThebandgapofSiCrangesfrom2.75–3.1dependingonthepolytype.SiChaslowerleakagecurrentsandhigherelectricfieldstrengththanSi.Duetoitswiderbandgap,SiCcanbeusedasasemiconductordeviceattemperaturesover600℃.TheprimaryfocusofSiCdeviceresearchiscurrentlyforpowerdevices.SiCpowerdevicesmayeventuallyfindapplicationaspowerdevicesinbrakingsystemsanddirectfuelinjection.High-temperaturesensorshavealsobeenfabricatedwithSiC.Bergetal.havedemonstratedaSiCbasedsensorforcylinderpressureincombustionengines[19]atupto350℃andCasadyetal.[20]haveshownaSiC-basedtemperaturesensorforuseto500℃.Atpresent,thewafersize,cost,anddeviceyieldhavemadeSiCdevicestooexpensiveforgeneralautomotiveuse.MostSiCdevicesarediscrete,asthelevelofintegrationachievedinSiCtodateislow.Passives:Thickandthin-filmchipresistorsaretypicallyratedto125℃.Naefeetal.[21]andSalmonetal.[22]haveshownthatthick-filmresistorscanbeusedattemperaturesabove200℃iftheallowableabsolutetoleranceis5%orgreater.Theresistorsstudiedwerespecificallyformulatedwithahighersofteningpointglass.Theminimumresistanceasafunctionoftemperaturewasshiftedfrom25℃to150℃tominimizethetemperaturecoefficientofresistance(TCR)overthetemperaturerangeto300℃.TaNandNiCrthin-filmresistorshavebeenshowntohavelessthan1%driftafter1000hat200℃[23].Thus,fortightertoleranceapplications,thin-filmchipresistorsarepreferred.Wirewoundresistorsprovideahigh-temperatureoptionforhigherpowerdissipationlevels[21].High-temperaturecapacitorspresentmoreofachallenge.Forlow-valuecapacitors,negative-positive-zero(NPO)ceramicandMOScapacitorsprovidelow-temperaturecoefficientofcapacitance(TCC)to200℃.NPOceramiccapacitorshavebeendemonstratedto500℃[24].Higherdielectricconstantceramics(X7R,X8R,X9U),usedtoachievethehighvolumetricefficiencynecessaryforlargercapacitorvalues,exhibitasignificantcapacitancedecreaseabovetheCurietemperature,whichistypicallybetween125℃to150℃.Asthetemperatureincreases,theleakagecurrentincreases,thedissipationfactorincreases,andthebreakdownstrengthdecreases.Increasingthedielectrictapethicknesstoincreasebreakdownstrengthreducesthecapacitanceandisatradeoff.X7Rceramiccapacitorshavebeenshowntobestablewhenstoredat200℃[23].X9Uchipcapacitorsarecommerciallyavailableforuseto200C,butthereisasignificantdecreaseincapacitanceabove150℃.Considerationmustalsobegiventothecapacitorelectrodesandterminations.NiisnowbeingsubstitutedforAgandPdAgtolowercapacitorcost.Theimpactofthischangeonhightemperaturereliabilitymustbeevaluated.ThesurfacefinishforceramiccapacitorterminationsistypicallySn.ThemeltingpointoftheSn(232℃)anditsinteractionwithpotentialsolders/brazesmustalsobeconsidered.Alternatesurfacefinishesmayberequired.Forhighervalue,low-voltagerequirements,wettantalumcapacitorsshowreasonablebehaviorat200℃ifthehermeticsealdoesnotloseintegrity[23].Aluminumelectrolyticsarealsoavailableforuseto150℃.Micapaper(260℃)andTeflonfilm(200℃)capacitorscanprovidehighervoltagecapability,butarelargeandbulky[25].High-temperaturecapacitorsarerelativelyexpensive.Volumetricallyefficient,high-voltage,highcapacitance,high-temperatureandlow-costcapacitorsarestillneeded.Standardtransformersandinductorcoreswithcopperwireandtefloninsulationaresuitableforoperationto200℃.Forhighertemperatureoperation,themagneticcore,theconductormetal(NiinsteadofCu)andinsulatormustbeselectedtobecompatiblewiththehighertemperatures[16,pp.651–652]Speciallydesignedtransformerscanbeusedto450℃to500℃,however,theyarelimitedinoperatingfrequency.Crystalsarerequiredforclockfrequencygenerationformicrocontrollers.Crystalswithacceptablefrequencyshiftoverthetemperaturerangefrom55℃to200℃havebeendemonstrated[22].However,theselectionofpackagingmaterialsandassemblyprocessforthecrystalarekeytohigh-temperatureperformanceandreliability.Forexample,epoxiesusedinassemblymustbecompatiblewith200℃operation.Substrates:Thick-filmsubstrateswithgoldmetallizationhavebeenusedincircuitsto500℃[21],[23].Palladiumsilver,platinumsilver,andsilverconductorsaremorecommonlyusedinautomotivehybridsforreducedcost.SilvermigrationhasbeenobservedwithanunpassivatedPdAgthick-filmconductorunderbiasat300℃[21].Thetime-to-failureneedstobeexaminedasafunctionoftemperatureandbiasvoltagewithandwithoutpassivation.Low-temperaturecofiredceramic(LTCC)andhigh-temperaturecofiredceramic(HTCC)arealsosuitableforhigh-temperatureautomotiveapplications.Embeddedresistorsarestandardtothick-filmhybrids,LTCC,andsomeHTCCtechnologies.Aspreviouslymentioned,thick-filmresistorshavebeendemonstratedattemperatures200℃.DielectrictapesforembeddedcapacitorshavealsobeendevelopedforLTCCandHTCC.However,theseembeddedcapacitorshavenotbeencharacterizedforhigh-temperatureuse.High-Tglaminatesarealsoavailableforfabricationofhightemperatureprintedwiringboards.Cyanateesters[Tg=250℃bydifferentialscanningcalorimetry(DSC)],polyimide(260℃byDSC),andliquidcrystalpolymers(Tm>280℃）provideoptionsforuseto200℃.Cyanateesterboardshavebeenusedsuccessfullyintestvehiclesat175℃,butfailedwhenexposedto250℃[26].Thehighercoefficientofthermalexpansion(CTE)ofthelaminatesubstratescomparedtotheceramicsmustbeconsideredintheselectionofcomponentattachmentmaterials.Thetemperaturelimitsofthelaminateswithrespecttoassemblytemperaturesmustalsobecarefullyconsidered.Workisongoingtodevelopandimplementembeddedresistorandcapacitortechnologyforlaminatesubstratesforconventionaltemperatureranges.Thistechnologyhasnotbeenextendedtohigh-temperatureapplications.Onemethodmanymanufacturersareusingtoaddressthehighertemperatureswhilemaintaininglowercostistheuseoflaminatesubstratesattachedtometal.ThetypicaldesigninvolvestheuseofhigherTg(+140℃andabove)laminatesubstratesattachedtoanaluminumplate(approximately2.54-mmthick)usingasheetorliquidadhesive.Toassistinthermalperformance,thelaminatesubstrateisoftenthinner(0.76mm)thantraditionalautomotivesubstratesforunder-the-hoodapplications.Whilethisdesignprovidesimprovedthermalperformance,theattachmentofthelaminatetoaluminumincreasestheCTEfortheoverallsubstrates.TheresultantCTEisverydependentontheabilityoftheattachmentmaterialtodecoupletheCTEbetweenthelaminatesubstrateandthemetalbacking.However,regardlessoftheattachmentmaterialused,thecombinationofthelaminateandmetalwillincreasetheCTEoftheoverallsubstrateabovethatofastand-alonelaminatesubstrate.ThisimpactcanbequitesignificantinthereliabilityperformanceforcomponentswithlowCTEvalues(suchasceramicchipresistors).Fig.9illustratestheimpactoftwolaminate-to-metalattachmentoptionscomparedtostandardlaminatesubstrates[27],[28].Thereliabilitydatapresentedisfor2512ceramicchipresistorsattachedtoa0.79-mm-thicklaminatesubstrateattachedtoaluminumusingtwoattachmentmaterials.Noticethatwhileonematerialsignificantlyoutperformstheother,botharelessreliablethanthesamechipresistorattachedtolaminatewithoutmetalbacking.Thisdecreaseinreliabilityisalsoexhibitedonsmallballgridarray(BGA)packages.Fig.10showsthereliabilityofa15-mmBGApackageattachedtolaminatecomparedtothesamepackageattachedtoalaminatesubstratewithmetalbacking[27],[28].Theattachmentmaterialusedforthemetal-backedsubstratewasthebestmaterialselectedfromprevioustesting.Noticeagainthatthemetal-backedsubstratedeterioratesthereliability.ThisreliabilitydeteriorationisofparticularconcernsincemanyICpackagesusedforautomotiveapplicationsareballgridarraypackagesandthepackagingtrendisforreducedpackagingsize.Thesepackagingtrendsmaketheuseofmetal-backedsubstratesdifficultfornextgenerationproducts.Onepotentialsolutiontotheabovereliabilityconcernistheuseofencapsulantsandunderfills.Fig.11illustrateshowconformalcoatingcanimprovecomponentreliabilityforsurfacemountchipresistors[27],[28].Noticethatthereliabilityvariesgreatlydependingonmaterialcomposition.However,forcomponentswhichmeetamarginallevelofreliability,conformalcoatingsmayassistthedesigninmeetingthetargetreliabilityrequirements.ThesamescenariocanbefoundforBGAunderfills.Typicalunderfillmaterialsmayextendthecomponentlifebyafactoroftwoormore.FormarginalICpackages,thisenhancementmayprovideenoughreliabilityimprovementtoallthedesignstomeetunder-the-hoodrequirements.Unfortunately,theimprovementsprovidedbyencapsulantsandunderfillsincreasethematerialcostandaddsoneormoremanufacturingprocessesformaterialdispenseandcure.Interconnections: