芯片測試原理課件

ICTestFundamental GongXiao-Long20131ICTestFundamental GongXiao-CourseContentsLesson1: OverviewofICTestLesson2: Open/ShortandDCtestLesson3: FunctionalTestLesson4: TestVectorbasicLesson5: ADC/DACLesson6: ACtestingLesson7: Scan/Bist/JtagtestingLesson8: RFtestingLesson9: TestprogramDevelopmentLesson10: TroubleShooting2CourseContentsLesson1: OverLesson1: OverviewofICTestTestcategoryTheTestSystemPMUPE-Card3Lesson1: OverviewofICTestTTestcategoryWaferTest—Thetestingofindividualdeviceswhentheyarestillinwaferform.Thisisthefirstattemptatseparatinggooddicefrombad.Thisactivityisalsocalledwafersortordiesort.PackageTest—Wafersarecutintoindividualdiceandeachdieisassembledintoapackage.Thepackageddeviceisthentestedtoinsurethattheassemblyprocesswascorrectlyperformedandtoverifythatthedevicestillmeetsitsdesignspecifications.Packagetestisalsocalledfinaltest.QualityAssuranceTest—Performedonasamplebasistoinsurethatthepackagetestwasperformedcorrectly.DeviceCharacterization—DeviceCharacterizationistheprocessofdeterminingtheoperatingextremesofindividualdeviceparameters.Pre/PostBurn-In—Thetestingofdevicesbeforeandaftertheyare"burnedin"toverifythattheprocessdidnotcausecertainparameterstodrift.Thisprocessweedsoutinfantmortalitydevices(thosewhichhaveadefectthatcausesthemtofailsoonaftertheyarefirstused)..4TestcategoryWaferTest—TheMilitaryTesting—Involvesperformingrigoroustestingoveratemperaturerangeanddocumentingtheresults.IncomingInspection—Testingofdevicesbyacustomertoinsurethequalityofthedevicespurchasedbeforeusingtheminanapplication.AssemblyVerification—Verifiesthatthedevicessurvivedtheassemblyprocessandthattheywereassembledcorrectly.Thetestsperformedduringassemblyverificationaresimilartothatofpackagetestingandmaybeasubsetofpackagetesting.Thisactivityisusuallyperformedoffshore.FailureAnalysis—Theprocessofanalyzingdevicefailurestodeterminewhythedevicefailed.Determiningthecauseofafailureyieldsinformationthatcanimprovedevicereliability.Testcategory5Testcategory5TheTestSystemThetestsystemiselectronicandmechanicalhardwareusedtosimulatetheoperatingconditionsthataDUTwillexperiencewhenusedinanapplication,sothatdefectivedevicescanbefound.ThetestsystemisoftenknownasATEorAutomatedTestEquipment.Thetestsystemhardwareiscontrolledbyacomputerwhichexecutesasetofinstructions(thetestprogram).Thetestermustpresentthecorrectvoltages,currents,timingsandfunctionalstatestotheDUTandmonitortheresponsefromthedeviceforeachtest.Thetestsystemthencomparestheresultofeachtesttopre-definedlimitsandapass/faildecisionismade.Atestsystemisactuallyacollectionofpowersupplies,meters,signalgenerators,patterngeneratorsandotherhardwareitemswhichallworkcollectivelyunderonemaincontroller.6TheTestSystemThetestsystemTheTestSystem7TheTestSystem7TheCPUisthesystemcontroller.Itcontainsthecomputerwhichcontrolsthetestsystemandprovidesameansofmovingdataintoandoutofthetestsystem.Mostnewtestsystemsofferanetworkinterfaceaswellasmagneticmediafordatatransfers.TheharddiskandCPUmemoryareusedtostoreinformationlocally;thevideodisplayandkeyboardareusedbythetestoperatortointeractwiththetestsystem.TheDCsubsystemcontainstheDevicePowerSupplies(DPS),theReferenceVoltageSupplies(RVS)andthePrecisionMeasurementUnit(PMU).TheDPSsuppliesvoltageandcurrenttotheDUTpowerpins(VDD/VCC).TheRVSsuppliesvoltagereferencesforlogic0andlogic1levelstothedriverandcomparatorcircuitrylocatedonthepinelectroniccards.ThesevoltagessetVIL,VIH,VOLandVOH.LessexpensiveandoldertestsystemsmayhavealimitednumberofRVSsupplies,soonlyalimitednumberofinputandoutputlevelscanbeprogrammedatonetime.WhentesterpinssharearesourcesuchastheRVS,thatresourceisconsideredasharedresource.Sometestsystemsaresaidtohaveatesterperpinarchitecturewhichmeansthattheyhavetheabilitytosetinputandoutputlevelsandtimingindependentlyforeachpin.Atesterpin,alsocalledtesterchannel,iscircuitryonthepinelectronicscardwhichsuppliesand/ordetectsvoltage,currentandtimingforoneDUTpin.TheTestSystem8TheCPUisthesystemcontrollEachtestsystemhashighspeedmemory,calledpatternmemoryorvectormemory,tostoretestvectorsortestpatterns.Testpatterns,alsoknownasthetruthtable,representthestatesofinputsandoutputsforthevariouslogicalfunctionsthatthedeviceisdesignedtoperform.Input,ordrive,patternsaresuppliedtotheDUTbythetestsystemfrompatternmemory.Output,orexpect,patternsarecomparedagainsttheresponsefromtheoutputpinsoftheDUT.Duringafunctionaltest,vectorpatternsareappliedtotheDUTandtheDUT'sresponsesaremonitored.IftheexpectedresponsedatadoesnotmatchtheoutputdatafromtheDUT,afunctionalfailureoccurs.Therearetwotypesoftestvectors--parallelvectorsandscanvectors.Manytestsystemssupportbothtypes.Thetimingsubsectionhasmemorytostoreformatting,maskingandtimesetdataforuseduringfunctionaltesting.Thesignalformats(waveshapes)andtimingedgemarkersareusedforDUTinputsignalsandstrobetimingforsamplingDUToutputsignals.ThetimingsubsectionreceivesdrivepatternsfrompatternmemoryandcombinesthemwithtimingandsignalformatinformationtocreateformatteddatawhichissenttothedriversectionofthepincardandthentotheDUT.SpecialOptionsincludesavarietyofpossibilitiessuchasalgorithmicpatterngeneratorsformemorytestorspecializedhardwaremodulesusedtoperformanalogtests.TheSystemClocksprovideameansofsynchronizingthemovementofinformationthroughoutthetestsystem.Theseclocksoftenrunatmuchhigherfrequenciesthanthefunctionaltestrate.Manytestsystemshavecalibrationcircuitrywhichcanautomaticallyverifyandcalibratethesystemtiming.TheTestSystem9EachtestsystemhashighspeePMUThePrecisionMeasurementUnit(PMU)isusedtomakeaccurateDCmeasurements.Itcanforcecurrentandmeasurevoltageorforcevoltageandmeasurecurrent.SometestsystemshaveonlyonecentralPMUthatmustbesharedacrossallpinchannelsofthetester.OthershavemorethanonePMUwhichaccessesmultiplechannels,typicallyingroupsofeightorsixteen.HighendtestsystemshavePMUperpincapability,whichhasaPMUoneverytesterchannel.PrecisionMeasurementUnit10PMUThePrecisionMeasurementUForceandMeasurementModesInATE,thetermforce(asinforcevoltageorforcecurrent)describestheapplicationofacertainvalueofvoltageorcurrentbythetestsystem.Applycanbesubstitutedforthewordforce.WhenprogrammingthePMU,theforcefunctionisselectedaseithercurrentorvoltage.Ifcurrentisforced,themeasurementmodeisautomaticallysettovoltage.Ifvoltageisforced,themeasurementmodeisautomaticallysettocurrent.Oncetheforcefunctionisselected,theforcevaluemustbeset.ForceandSenseLinesToimprovethevoltageforcingaccuracyofthePMU,afourwiresystemisused.Fourwiresystemsuse2forcelinestocarrycurrentand2senselinestomonitorthevoltageatthepointofinterest(usuallytheDUT).Ohm‘sLawstatesthatavoltageisproducedacrossaresistancewhencurrentflowsthroughtheresistance.Allwirehasresistanceso,dependingonthecurrentthroughtheforcelines,thevoltageattheDUTisdifferentfromthevoltageatthePMUforceunitoutput.Using2separate(non-currentcarrying)sensewirestomeasurethevoltageattheDUTkeepsthevoltagedropcausedbycurrentflowthroughtheforcelinesfromcausinganerrororoffsetinthevoltage.ThepointatwhichtheforceandsenselineareconnectedtogetheriscalledtheKelvinConnectPoint.PMU11ForceandMeasurementModesPMURangeSettingsAPMUforcerangeandmeasurementrangemustbeselected.Properrangeselectioninsuresthemostaccuratetestresult.BeawarethattheforceandmeasurerangeshavealimitingeffectonthePMU.TheforcerangewilldeterminethemaximumforcingcapabilityofthePMU,soifthePMUisprogrammedtoforce5Voltsandthe2Voltforcerangehasbeenselected,only2Voltswillbeforced.Likewise,ifthe1mAmeasurementrangeisselected,themaximumcurrentthatcanbemeasuredis1mAregardlessoftheactualcurrentflow.ItisimportanttonotethatneithertheforcenorthemeasurementrangeofthePMUshouldbechangedwhileitisconnectedtoaDUT.ChangingtherangecausesnoisespikesthatmaydamagetheDUT.Anoisespikeiswhenasignallevelabruptlychangesitsvoltagelevelforaveryshorttime.Anoisespikeisalsocalledaglitch.LimitSettingsThePMUhastwoprogrammablemeasurementlimits—anupperandalowerlimit.Thelimitsmaybeusedindividually(onelimitenabledwhiletheotherisdisabled)ortheymaybeusedtogether(bothlimitsenabled).TheupperlimitisusedtomakeaFailGreaterThancomparisonandthelowerlimittomakeaFailLessThancomparison.Failingthe"FailGreaterThan"limitmeansthemeasuredvaluewasmorepositivethantheupperlimitsetting.Failingthe"FailLessThan"limitmeansthemeasuredvaluewasmorenegativethanthelower-limitsetting.PMU12RangeSettingsPMU12PMUClampSettingsMostPrecisionMeasurementUnitshavevoltageandcurrentclampswhicharesetfromwithinatestprogram.AclampisacircuitthatlimitstheamountofvoltageorcurrentthatissuppliedbythePMUduringatestinordertoprotectthetestoperator,thetesthardwareandtheDUT.13PMUClampSettings13WhenthePMUisusedinForceVoltagemode,acurrentclampmustbesettolimitthemaximumcurrentwhichflowsduringthetest.Whenforcingvoltage,aPMUdeliversasmuchcurrentasnecessarytosustainthevoltage.IfaDUTpinisshortedtoground(oranothersupply),theforcingunitwillincreasethecurrenttotrytoforcethepintotheprogrammedvoltage.ThismayresultinalargeenoughcurrentflowthroughtheDUTpintoburnprobecards,circuittraces,pinelectronicscomponents,fingers,adjacentDUTs,etc.Whenforcingvoltage,thePMUmeasurescurrent.BecausethecurrentclamplimitstheamountofcurrentsuppliedbythePMU,thecurrentclampvaluemustbesetoutsideofthetestlimitsotherwisethecurrentclampwillpreventa"toomuchcurrent"failure.Previouspage’sFigureshowsthePMUforcing5.0Vacrossa250Ohmload.Inactualtesting,theDUTistheresistiveload.FromOhm'sLaw(I=E/R)weknowthatthe250Ohmloadwillrestrictthecurrentflowto20mAduringthistest.Thedevicespecificationmaystatethatthemaximumacceptablecurrentis25mA.ThismeansthefaillimitwouldbesettoFailGT25mAandthecurrentclampcouldbesetto30mA.IfadefectiveDUTpresentsaloadof10Ohms,theresultingcurrentwillbe500mAunlessacurrentclampisprogrammedtolimitthecurrent.Acurrentflowof500mAmaycausedamagetothetestsystem,theinterfacehardwareortheDUT.However,ifacurrentclampisprogrammedto30mAthemaximumcurrentflowwouldbelimitedbythedampcircuittoamuchsafervalue."Why30mA?"youmayask.30mAisgreaterthanthefaillimitof25mA,allowingthetesttofailwhenadefectivedeviceisencountered,butthecurrentwillbelimitedtoasafevalue.Theclampvaluemustalwaysbesetoutsideofthefaillimits;ifnot,thetestwillneverfail.PMU14WhenthePMUisusedinForceSimilarwithcurrentclampPMU15SimilarwithcurrentclampPMUThepinelectronics(alsocalledthePinCard,PE,PECorI/Ocard)istheinterfacebetweenthetestsystemresourcesandtheDUT.ItsuppliesinputsignalstotheDUTandreceivesoutputsignalsfromtheDUT.EachtestsystemhasitsownuniquedesignbutgenerallythePEcircuitrywillcontain:?Drivercircuitrytosupplyinputsignals.?I/Oswitchingcircuitryforturningdriversandcurrentloadsonandoff.?VoltageComparatorcircuitryfordetectingoutputlevels.?AconnectionpointtothePMU.?Programmablecurrentloads.?Possiblyadditionalcircuitryformakinghighspeedcurrentmeasurements.?PossiblyaperpinPMUAlthoughtherearemanyvariationsofthisdesign,Figure3-5representsasingletesterchannelonatypicalpinelectronicscardforadigitaltestsystem.PE-Card16Thepinelectronics(alsocallPE-Card17PE-Card17TheDriverThedrivercircuitryreceivesformattedsignals,calledFDATA,fromthehighspeedsectionofthetestsystem.Asthesignalpassesthroughthedriver,theVIL/VIHreferencesfromtheReferenceVoltageSupplies(RVS)areappliedtotheformatteddata.IftheFDATAinstructsthedrivertodrivetoalogic0,thedriverwilldrivetotheVILreference.VIL(VoltageInLow)representsthemaximumguaranteedvoltagevaluethatcanbeappliedtoaninputandstillberecognizedasalogic0bytheDUTcircuitry.IftheFDATAinstructsthedrivertodrivetoalogic1,thedriverwilldrivetotheVIHreference.VIH(VoltageInHigh)representstheguaranteedminimumvoltagevaluethatcanbeappliedtoaninputandstillberecognizedasalogic1bytheDUTcircuitry.Whenthetesterchannelisprogrammedasaninput,FlFETturnsonandtheK1relayisclosedallowingthesignalfromthedrivertopassthroughtotheDUT.Whenthetesterchannelisprogrammedasanoutputorisina"don'tcare"modetheFlFETisturnedoffandthesignalfromthedriverwillnotpassthroughtotheDUT.TheFlFETisaFieldEffectTransistorusedasaveryhighspeedswitch.Itisolatesthedrivercircuitryfromthedeviceundertest.TheFlFETisusedduringIOswitching,whichiswhentheDUTalternatesbetweenreceivingdatafromthetestsystem(readingdata)andsupplyingdatatothetestsystem(writingdata).Thesamepinsfunctionasbothinputsandoutputs.Ifthetesterchannelisprogrammedasaninput,theFETison.IfthetesterchannelisnotprogrammedasaninputtheFlFETisoff,whichpreventsthedriversignalfromreachingthedeviceundertest.ItisimportanttoinsurethattheDUTandthedriverarenottryingtodriveavoltageontothesametesterchannelatthesametime.ThisiscalledanI/Oconflictoxbuscontention.PE-Card18TheDriverPE-Card18CurrentLoadsTheCurrentLoads,alsoknownasDynamicLoadsorProgrammableCurrentLoads,actasaloadtotheDUToutputsduringfunctionaltestsandcanbeprogrammedtosupplypositiveandnegativecurrents.PositivecurrentflowsfromthetestsystemintothedeviceandnegativecurrentflowsfromtheDUTintothetestsystem.ThedynamicloadsprovidebothIOH(CurrentOutHigh),whichistheamountofcurrentthataDUToutputmustsourcewhendrivingalogic1,andIOLcurrent(CurrentOutLow),whichistheamountofcurrentthataDUToutputmustsinkwhendrivingalogic0.AftertheIOLandIOHcurrentvaluesaresetbythetestprogram,theVREFvoltageisusedtosettheswitchingpointoftheIOLandIOHcurrents.TheswitchingpointistheoutputvoltageabovewhichIOHflowsandbelowwhichIOLflows.WhentheoutputvoltagefromthedeviceundertestismorenegativethanVREF,IOLcurrentflows.WhentheoutputvoltagefromthedeviceundertestismorepositivethanVREF,IOHcurrentflows.ThecurrentloadsarealsousedduringthefunctionalTri-State?testsandthefunctionalopensandshortstest.TheF2FETisalsoafieldeffecttransistorusedasahighspeedswitch.TheF2FETisolatesthecurrentloadcircuitryfromthedeviceundertestandisusedduringIOswitching.Ifthetesterchannelisprogrammedasanoutput,F2ison,allowingcurrenttoflowtoandfromthedeviceundertest.Ifthetesterchannelisprogrammedasaninput,F2isoff.PE-Card19CurrentLoadsPE-Card19TheVoltageComparatorsTheVoltageComparatorsareusedduringfunctionaltestingtocomparetheoutputvoltageofthedeviceundertesttoreferencevoltagessuppliedbytheRVS.TheRVSsuppliesareferenceforavalidlogic1(VOH)andavalidlogic0(VOL).IftheDUToutputvoltageisequaltoorlessthanVOL,itisrecognizedasalogiczero.IftheDUToutputvoltageisequaltoorgreaterthanVOH,itisrecognizedasalogicone.IftheoutputvoltageisgreaterthanVOLbutlessthanVOH,itisconsideredtobeaTri-State?levelorabadoutput.ThePMUConnectionWhenthePMUconnectstoadevicepin,theK1relayisopenedfirst,thentheK2relayisclosed.ThissequenceisolatesthePMUfromtheI/Ocircuitryofthepinelectronicscard.TheHighSpeedCurrentComparatorsSometestsystemsofferawaytomeasuresmallcurrentsquicklyasanalternativetohavingaPMUforeachtesterchannel.Currentcomparatorsareusedtomakehighspeedleakagemeasurements.TheK3relayconnectsthecurrentcomparatorstothepinundertest.IfthetestsystemhasPMUperpincapability,thecurrentcomparatorsarenotnecessary.ThePPPMUSometestsystemsofferaperpinPMU(PPPMU)thatallowsthetestsystemtomeasureeithervoltageorcurrentoneverypinsimultaneously.LikethePMUthePPPMUcanforcecurrentandmeasurevoltageorforcevoltageandmeasurecurrent.PPPMUstypicallylackallthecapabilityofthestandardsystemPMU.PE-Card20TheVoltageComparatorsPE-CardLesson2: Open/ShortandDCtestWhyTestforOpensandShorts?OpensandShortsSerialStaticMethodDCtestintroduce21Lesson2: Open/ShortandDCteWhyTestforOpensandShorts?Theopens/shortstest(alsocalledcontinuityorcontacttest)verifiesthat,duringadevicetest,electricalcontactismadetoallsignalpinsontheDUTandthatnosignalpinisshortedtoanothersignalpinorpower/ground.Devicecostisdirectlyrelatedtohowlongittakestotesteachdevice.Oneofthebestwaystoreduceaveragetesttimeperdeviceistorejectbaddevicesassoonaspossible.Theopens/shortstestdeterminesveryquicklywhetheradevicehasshortedpins,missingbondwires,apindamagedfromstaticelectricity,amanufacturingdefect,etc.Theopens/shortstestcanalsopointtotestsystemrelatedproblemssuchasawafertestprobecardoradevicetestsocketwhichisnotmakingcorrectcontact.22WhyTestforOpensandShorts?OpensandShortsSerialStaticMethodTestconditionsforanopens/shortstestarenotnormallydefinedinthedevicespecificationordatabookspecification,buttherearestandardvalueswhichapplytomoststandarddevicetypes.Thesestandardvaluesarepresentedintheguidelineshere.Totestforopens/shorts,firstgroundalldevicepinsincludingpowerandgroundpins.Next,connectthePMUtoasingledevicepinandforceacurrentwhichwillforwardbiasoneoftheprotectiondiodes.(SeeFiguresnextpage.)Anegativecurrentwillforwardbiasthediodetoground;apositivecurrentwillforwardbiasthediodetoVDD.Acurrentintherangeof100μAto500μAshouldbeadequate.Onceforwardbiased,thevoltagedropacrosstheprotectionstructurecanbesensed(typically0.65volt).Thesensedvoltagemaychangebetweenvarioustechnologiesanddesigns,but0.65Visgoodformostsiliconbaseddevices.SincethePMUwillbeprogrammedtoforcecurrent,avoltageclampmustbeprogrammedtolimitthevoltageproducedwhenanopenpinistested.Atypicalclampvaluefortheopens/shortstestis3V.Whenanopenpinistested,themeasuredresultwillbetheclampvoltage(3V).TheadvantageoftheSerial/StaticopensandshortstestisthatitproducesDCmeasurements.Whenafailureoccurs,theexactmeasuredvoltagemaybeexaminedfromthedata-loggedresults.Thevoltagevalueclearlyindicateswhetherthefailurewascausedbyashortedconditionoranopencondition.ThedisadvantageisthetimerequiredtomaketheindividualDCmeasurementoneachpin.23OpensandShortsSerialStaticOpensandShortsSerialStaticMethod24OpensandShortsSerialStatic2525DCTestVOH/IOHVOHrepresentstheminimumvoltage(V)producedbyanoutput(O)whentheoutputisinthelogic1(High)state.IOHrepresentsthecurrentsourcingcapabilities(I)ofanoutput(O)whentheoutputisinthelogic1(High)state.ThefollowingtableillustratestheVOH/IOHspecificationWhyTestforVOH/IOH?TheVOH/IOHtestmeasurestheresistanceofanoutputpinwhentheoutputisinthelogic1state.ThistestinsuresthattheresistanceoftheoutputmeetsthedesignparametersandguaranteesthattheoutputwillprovidethespecifiedIOHcurrentwhilemaintainingtheproperVOHvoltage.26DCTestVOH/IOHVOHrepreVOH/IOH—Serial/StaticTestMethodTheseparametersmaybeverifiedeitherstaticallyordynamically(dynamicVOHwillbediscussedlater).Toperformastatic(DC)test,thedeviceispreconditionedtosettheoutput(s)intothelogic1state,theDCmeasurementsystem(PMU)isconnectedtothepinundertest,theIOHcurrentisforcedandtheresultantvoltageismeasuredandcomparedtotheVOHspecification.IfthemeasuredvoltageislessthantheVOHlimit,thetestfails.Thisprocessisrepeateduntilallpinshavebeenverifiedinthehighoutputstate.Thistestmayrequirerunningmorethanonepreconditioningsequencetosetalloutputstothelogic1state.DCTestVOH/IOH27VOH/IOH—Serial/StaticTestMetDCTestVOL/IOLVOLrepresentsthemaximumvoltage(V)producedbyanoutput(O)whentheoutputisinthelogic0(Low)state.IOLrepresentsthecurrentsinkingcapabilities(I)ofanoutput(O)whentheoutputisinthelogic0(Low)state.ThetablebelowshowsaVOLspecification:WhyTestforVOL/IOL?TheVOL/IOLtestmeasurestheresistanceofanoutputpinwhentheoutputisinthelogic0state.ThistestinsuresthattheresistanceoftheoutputmeetsthedesignparametersandguaranteesthattheoutputwillprovidethespecifiedIOLcurrentwithoutexceedingtheVOLvoltage.Inotherwords,thedeviceoutputpinsmustsinkatleastaspecifiedminimumamountofcurrentandstayinthecorrectlogicstate.28DCTestVOL/IOLVOLrepreDCTestVOL/IOLVOL/IOL—Serial/StaticTestMethodTheVOL/IOLparametersmaybeverifiedeitherstaticallyordynamically(dynamicVOLwillbediscussedlater).Toperformastatic(DC)test,thedeviceispreconditionedtosettheoutput(s)tothelogic0state.TheDCmeasurementsystem(PMU)isthenconnectedtothepinundertest,theIOLcurrentisforcedandtheresultantvoltageismeasuredandcomparedtotheVOLspecification.IfthemeasuredvoltageisgreaterthantheVOLlimitthetestfails.Thisprocessisrepeatedforeachpinuntilallpinshavebeenverifiedinthelowoutputstate.Thistestmayrequirerunningmorethanonepreconditioningsequencetosetalloutputstothelogic0state.29DCTestVOL/IOLVOL/IOL—SDCTestGrossIDDIDDrepresentsthecurrent(I)whichflowsdraintodrain(DD)withinaCMOScircuit.WhentestingTTLdevicesthistestiscalledICC.ICCrepresentsthecurrent(I)whichflowscollectortocollector(CC)withinaTTLcircuit.Grossindicatesthatthetestismadewithconditionsthathavebeenrelaxedfromthosedefinedinthedevicespecification.WhyTestforGrossIDDCurrents?ThepurposeofthegrossIDDtestistoquicklydetermineifitisreasonabletocontinuetotesttheDUT.ThegrossIDDtestisoftenperformedimmediatelyaftertheopens/shortstestandisthefirsttestmadeafterinitiallypoweringuptheDUT.IftheDUTisdrawingexcessivecurrent,thetesthardwaremaybedamaged.Whenthistestfails,devicepowerisimmediatelyshutoffandtheDUTisrejected.30DCTestGrossIDDIDDrepreDCTestGrossIDDTestMethodforGrossIDDCurrentsThegrossIDDtestisameasurementofcurrentflowintotheVDDpin.Thetestisofteninstalledinthewaferprobetestprogramanditmayalsobeincludedintheproductiontestprogram.Thistestistypicallyperformedbeforeanyfunctionaltest,soitisnotknowniftheDUTcanbesuccessfullypreconditioned.ThedevicemustbecorrectlypreconditionedtotestforIDDcurrentsasdefinedinthedevicespecification.Sincefunctionality(andthereforepreconditioning)isnotguaranteedatthispointwithinthetestflow,theIDDspecificationmustberelaxed.Thetestisnormallyperformedbyfirstsettingallinputsloworallinputshighorbyresettingthedevice.TypicallyVILissettozerovoltsandVIHissettoVDD.Outputshavenoloads—outputcurrentscouldincreaseIDDandwronglycausethetesttofail.TheexactpreconditioningdependsonthefunctionoftheDUTandshouldbekeptassimpleaspossible.ThepurposeofpreconditioningistoputtheDUTintoastablecondition.OncetheDUTispreconditionedthetotalsupplycurrentflowingintothedeviceismeasured.IfthemeasuredcurrentexceedsthetestlimitthetestresultisconsideredafailureandtheDUTisrejectedwithoutfurthertesting.ToestablishthegrossIDDtestlimit,testasamplenumberofdevicesandobservetheIDDcurrentreadings.Thensettestlimitsbasedontheobservedreadings.ThegrossIDDtestlimitmaybesetto2or3timestheIDDlimitfoundinthedevicespecification.ThistestmayalsobeusedasamonitortoindicatetherangeofIDDcurrentthedevicedraws.TheinitialtestspecificationmaystatethattheIDDcurrentlimitis"TBD"(tobedetermined).Ifso,asamplenumberofdevicesshouldbetestedandtheIDDreadingsobserved.ThecurrentlimitforthegrossIDDtestshouldthenbesettwoorthreetimeshigherthantheaveragereading.31DCTestGrossIDDTestMethDCTestGrossIDD32DCTestGrossIDD32WhyTestforStaticIDDCurrent?ThestaticIDDtestinsuresthattheDUTwillnotconsumemorecurrentthanthevaluestatedinthedevicespecification,whentheDUTispreconditionedtoitslowestcurrentconsumptionlogicstate.Thismeasurementisextremelyimportantforbatteryoperateddevices.ItisalsoagoodwaytoidentifyprocessingproblemswithCMOSdevices.DCTestStaticIDD33WhyTestforStaticIDDCurrenDCTestIDDQTheIDDQtestmeasuresthequiescentcurrentundervaryinglogicconditionsandprovidesimprovedtestcoverageascomparedtothestandardStaticIDDtest.Toperformthis