LCD Monitor Reliability Issues

Copyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTestingFocusingonKeyAreaswhichaffectReliabilityCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•KeycommoditieswhichcauserepetitiveproblemsforallLCDMonitorSuppliers–InverterUnder-ratedFuseFails,Solderproblems–LCDWeakTabbonds/ITOcorrosion–LCDGapMuradefects–MotherboardMcuFirmwareUpgrades–MotherboardproblemscausingDistortedDisplay–PoorCableconnectionbetweenLCD/MotherBd–PowerBoardvoltageoverload–PowerAdapterissueswithVoltageSpikesleadingtoDisplayFlashing/IntermittentDisplayLoss–NFFproblemswhichleadtoeventualfailure–PowerAdapterFailures–BackLightperformancedegradationCopyright©2004reliabilitysolutionsallrightsreservedLCDMONITORQ&RPROBLEMS•InverterFailures–Veryhigh%ofallLCDmonitortypesundergoingrepairrequireInverterSwap/Upgrade–Typicalproblems;•Under-ratedfusesbeingoverstressed,causinglonglifeproblemsandhighreturnrates(oftenepidemic)–Solutionexpensivewithupgradecostsofaround$5perboard•RoguesignalsleadingtoFOSnoise,oftenneedscapaddtotakesignaltoground•Requiresinvertertestat10-15%abovenormalvoltageinputwithrepeatedpowerswitchingandlongperiodsofpoweron•ThermalShockTestingisfastandeffectiveinfindingweaksolderjointsandpoorlysolderedSMTcomponents–Useextremetemppointsof+60and–20degC–30minsineachenvironment,moveimmediatelyafter30minsintocoldorhotenvironment–Cycleminimumof4timesproviding4hrthermalshockconditions–RunElevatedtemptestatminimum50degCwithsameinvertersbuiltintotestmonitors,runnormalORTtestprofileCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•LCDReliability–OftenTabdefectscanbeexcessiveduetopoorbodingprocess•Poorbondingevidentif‘TabPeelTest’isperformedonsampleLCDpanels–Poorcontrolofproductionenvironmentcanresultinmoisture/chemicalstrappedbetweenTabchipcarrierandGlasspanel•WillresultinacceleratedITOcorrosionandlossofsignalleadingtodeadlineonscreenwhichcannotberepaired•Acceleratedtestinginhumidconditionsveryeffectiveinacceleratingfailuremechanism,LCDsuppliermustbeabletoshowEnvtestdatatoproveLCDpanelrobustnessCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•CORROSIONCAUSEDBYINTIALCONTAMINATION.CREATINGCONDUCTIVITY(SHORTCIRCUITBETWEENITOLINES)ITOLINESCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTestingITOCORROSIONITOLINESCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•NFFPROBLEMS–Oftendifficulttore-createtheproblem–IfNFF20-25%,assumeinherentproblemexists•Inherentdesignproblemorgraphicscard/monitorinterfaceproblem•Poweradaptercomponenttolerance?–LCDmonitorextendedB/Iiseffectiveinfinding‘true’defectswhicharewaitingtohappen•OftenmeansNFFreturnsfromcustomerneedb/iat40degforupto16-24hrsforhardfailtooccur•FocusonNFFreturnsatearlystageinnewmonitorlifetimewillbringsignificantbenefits•RepetitiveStressTestingSuccessfulatbringingNFFproblemstoHarddefectCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•PowerAdapterFailures–Oftencausedbychangeofsource/componentsusedcreatingproblemwithVoltageSpikesaboveMonitorDesignspec•RecentCatastrophicProblemforTaiwanSuppliercausedbymissingcapacitoronInputVoltagelinesbetweenearthandground•NewSuppliernotfullyverified,Adaptersamplesshouldhavebeenstrippeddownandcomparedindetailtooriginalsource–TestingofAdaptershouldInclude;•OutputVoltagesof+veandGndlinesshouldbesmoothwithvariableloadappliedunderdifferingtempconditions(0degCto+50),checkforandmeasurespikes•CheckoutputfromtransformertocheckACtoDCconversionwithconstantDC,checkingsecondaryoutputpins(normally2pins),changeACfromoutertolerancelevelstowithintolerance(InputVoltageandFrequency)•EnsurePowerConsumptionofadapterundervaryingloadsiswithinspec.Ifinputloadisvariedandpowerconsumptionisexcessive,adapterwillwear-outearly.If20Wrequiredbymonitor,butonoccasionpulls30or40W(sayinverterfails),adaptershouldshutdowntopreventLCDdamageCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•B/Lperformancedegradation(18”MonitorExample)ChartTitle050100150200250300350400450500125132034315244801192041222712970138891397114135141521418514739BRIGHTNESSPower(BRIGHTNESS)Copyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•B/Lperformancedegradation–Oftenhigherspecmonitorsrun24hrs/day,7daysperweekinBanking/StockExchangeapplications•36mthwarrantystillprovidedtothecorporateaccounts•Annualpoweronusagewillaverage8500hrs•Monitorswillrequiretohavebrightnessof150cd/m2tobeacceptabletocustomer–MustspecifyB/LspecwithLCDSupplierasminimalbrightnessof150cd/m2afterB/LON-Timeof12,000hrsCopyright©2004reliabilitysolutionsallrightsreservedLCDMonitorReliabilityTesting•Summary–RangeofCommodityTestsneedtobedefinedandwhereSupplierisinvolved,Suppliermustperformasmuchtestingaspossible–MustlookBEYONDNormalTestApproachandbeInnovative–RequireawelldocumentedprogrammeofDesignQAtests–Changetraditionalengrolestoprovidetimefornewtestapproach