ReliabilityIntroductionDefinitionReliabilityistheabilityofapersonorsystemtoperformandmaintainitsfunctionsinroutinecircumstances,aswellashostileorunexpectedcircumstancesBath-tubcurve3stagesEarlyfailurestageRandomfailurestage/steadystatefailurestageWearoutfailurestageThesefailuresaretypicallycausedbymanufacturingerrors,andsystem’sorintrinsicdefects.Solderingissue,PCBfabissueChipfailureduringtransportation,storage,handling,mounting,Howcanweavoidthis?Properandstabilizedmounting/solderingprocess“Burn-in”isverypopularusedtoscreentheearlyfailure.Earlyfailurestage

Thesefailuresaretypicallyoccurredduringnormaloperation,causedbychangingofoperatingcondition,inrushorotherunexpectedloadingchange.Howtoreducetherandomfailurerateandextendtheproductlife?ProperlyderatingwhendesignAddredundantmechanismorFRUforweakpoints.RandomfailurestageThesefailuresareusuallycausedbycyclicstress,mechanicalwear,chemicalreaction,andsoon.Thesefailurestypicallyoccuratanincreasingrate.WearoutfailurestageThermalHigh/lowtemperature/thermalcyclic/thermalshockHumidityLowhumidity/HighhumidityVoltageVoltagefluctuationanddriftingVibration/shockCriticalforcomponentswithbigsize,andmechanicalpartAltitudeheatdissipationismostimportantfactorforelectronicsproductsOthersRFemission,Conductedemission,surgeetc.StressEffectsimpactreliabilityTemperatureHumidityElectricalstressQualityfactorShockandvibrationSoftwarerobustnessTestequipment:RegularthermalchamberTestequipments-ThermalshockmachineTestequipments–vibrationmachineTestequipments–shockmachineTestequipments–dropmachineTestequipments–dropmachineOtherequipmentTerms-1Failurerate:λ,usuallyexpressedbyFailuresintime(FIT),calculatedin109hoursEg:thefollowfailureratesaresame100sample,after108hours,50samplesfailed.ThentheFITvalueis51000samples,after106hoursrunning,5samplesfailed.ThentheFITvalueis5MTBF:meantimebetweenfailuresMTBF=1/λ=109/FITvalueEg:theMTBFfortheabovesampleis2x108hoursTerms-2FMEA:FailuremodeandeffectsanalysisMTTF:MeantimetofailureConfidencelevel:towhatextendthedataorpredictwillbeconfidentFailurerate(λ):Failurerateisthefrequencywithwhichanengineeredsystemorcomponentfails,expressedforexampleinfailuresperhour,failuresper day,alsotherealsobeFIT(Failuresintime,whichis109devicehours)Probability: Standsfortheprobabilitythataproductcanworkwithoutfailure,P=1-λχ2distribution:isoneofthewidelyusedtheoreticalprobabilitydistributionininferentialstatistics.ThedistributionisaspecialcaseofGammadistributionwiththek=ν/2,θ=2,Formoreterms,pleaseGoogleitandreadreliabilitybooksReliabilitypredictionMIL-HDBK-217FTelcordiaSR332NSWCMechanicalPRISMCNET93/RDF2000HRD5GetMTBFviatestAssumptionThefailureratefunctionfollowstheexponentialdistributionThereliabilityfunctionofanexponentialdistributionThentheMTBFcanbecalculatedasbelowMTBF=WhereristhenumberoffailuresandCListheconfidencelevel,Tcanbedevicetime(samplenumberxtestduration).GetMTBFviatest-example50samplesrunningreliabilitydemonstratetest(RDT),afterrunning200days,2samplesfailed,pleasepredicttheMTBFbythefailuredataat90%confidentialleveland95%confidentiallevel.Weassumethisproductisexponentialmodelbasedχ2[2(2+1)],90%CL)=10.645χ2[2(2+1)],95%CL)=12.592MTBF90%CL=2T/χ2(2r+2,90%CL)=2x50x200x24/10.645=45091hoursMTBF95%CL=2T/χ2(2r+2,95%CL)=2x50x200x24/12.592=38119hoursEffectsimpactreliabilityTemperatureHumidityElectricalstressQualityfactorShockandvibrationSoftwarerobustnessAf(TH)=

(RH1/RH0)ne(Ea/k)*((1/T0)-(1/T1)WhereEaisactivationenergy,Typicallyinelectronics,thevalueofsemiconductorwillbe0.3eVto0.4eV;thevalueofpassivecomponentswillbe0.15eVto0.4eV,thisvalueisreferredtotheUTERDF2000reliabilitydatahandbook.nisavarianttomaterial,typicallythenvalueforsemiconductoris2kistheBoltzmannConstant,thevalueis8.617?3324(78)×10?5eV/KT0isthenormaloperatingtemperature,andT1istheaccelerationtesttemperature,theyareexpressedinKelvinthermometricscaleTemperatureaccelerationfactor(Af(TH))-eg:Af(TH)inMTBFperditioninRDTtest50samplesrunningreliabilitydemonstratetest(RDT),afterrunning200daysat40?C,90%RHcondition,2samplesfailed,pleasepredicttheMTBFbythefailuredataat90%confidentialleveland95%confidential

levelat25?C,60%RH.ElectricalstressfactorAf(E)Af(E)canbeexpressasequation Af(E)=em(p1-p0)

wheremstandsfordifferentseriesofcurvefordifferenttypeofcomponents,pleaserefertoSR-332,MIL-HDBK-217,andRDF2000etc.Thisisafactoreffectedbythechipcomponentprovider.4levelsareseparatedinSR-332.Qualitylevel0:Af(quality)=6Qualitylevel1:Af(quality)=3Qualitylevel2:Af(quality)=1Qualitylevel3:Af(quality)=0.8RefertoTelcordiaSR-332fordetail.

QualitylevelfactorThisisafactoreffectedbythechipcomponentprovider.5levelsareseparatedinSR-332.Level1:(Ground,Fixed,Controlled)GB:Af(s/v)=1Level2:(Ground,Fixed,unc