reliabilityengineering spec.docx
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reliabilityengineering spec.docx
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reliabilityengineeringspec
EngineeringSpecs
THEROADMAPTORELIABILITY
TESTING
MIKEWILLEY
PARAGONINOVATIONS,INC.
671N.PlanoRoadSuite203
Richardson,TX75081-2959
(972)680-2900Fax:
(972)680-0300
EngineeringSpecs
THEROADMAPTORELIABILITYTESTING
ABSTRACT
Manycompaniesguaranteetheirproducts,butfewworktheprocesstodeterminetheirrealriskandestimatedfailingpoint.Somegeneralprocedurescompaniescanapplytotheirownreliabilitytestinganalysiswillbediscussed,allowingcompaniestochecktheirownriskanalysisandimprovetheirtesting.Designverificationtesting(DVT)usestheengineeringspecificationasitsroadmap.TheDVTestablishesconformityofthecompleteddesignandthemanufacturedproductwiththeoriginalengineeringspecification.Thetestingcoversthefunctionsoftheproductanditsinteractionwithotherdevices.Alsotestedistheabilityoftheproducttoworkoverthespecifiedrangeofenvironmentalconditions.Andlast,theproductmustconformtotheappropriatesafetystandardsandregulatoryagencies.Lifetimetestingisusedtoverifyiftheproductmeetstheproductlifedesignobjectives.Automatedroundtheclockoperationofthedevicepermitsamanufacturertosimulateacceleratedusagewiththegoalofstatisticallyestimatingwearandtearoverthelifetimeoftheproduct.
SCOPE
Thispaperwillcoverthreeelementsofreliabilitytesting.Designverificationtesting(DVT)ensuresthatthedesignoftheproductmeetsallrequirements.Reliabilityanalysisdetermineshowphysicalfailures(basedonfatigueandwear)overtime.Systemburn-intestinghelpsacceleratetheoccurrenceofearlylifefailures.Reliabilitytrackingandanalysishelpsvalidateandrefinetheotherelementsofreliabilitytesting.
Theseelementscomprisethecontinuumofreliabilityanalysis.Wewilldescribeeachelementandhowtheyinterrelate.Wewillalsocoverpracticalmethodsofimplementingareliability-testingprogramforembeddedsystemsdevelopmentandproduction.
Embeddedsystemsaretypicallycomprisedofmechanical,electronic,electromechanical,andfirmware.Reliabilitytestingrelatestoalloftheseareas,thispaperwillpayspecialattentiontotheelectronicandelectromechanicalaspectsofreliabilitytesting,anddiscusstheotherareasonlybriefly.
INTRODUCTION
Whenwetalkaboutreliabilitywearediscussingthemostfundamentalmeasureofquality.Everyproductisdesignedandbuilttoperformsomefunction.Aslongasitcontinuestoperformthatfunctiontheproductisdeemedtobereliable.Reliabilityalwaysinfluencesthemarketreceptionandperceptionofaproduct.Forembeddedsystemsreliabilitymayalsobeamatteroflifeanddeath.
Ithaslongbeenestablishedthatreliabilitycanbecomputedmathematicallyforcertainelectronicdevices.Oftenmisunderstood,however,isthereasonthatwecancomputereliabilitybasedonlyonthenumberofcomponents,theircomplexity,andtheoperatingenvironment.TheUnitedStatesMilitaryandoldBellSystemrecognizedthatstandardizedprocessesledtopredictablereliabilityonpurchasedsystems.Bothhaveestablishedrigorousstandardsforprocurementandperformancetrackingonsystemsanddevices.TheresultsofthistrackingareaccumulatedintheMilitaryHandbookMIL-HDBK-217andTelcordiaTR-332.Thesedocumentsallowanyonebuildingelectronicsproductstolearnfromtheirexperience.
ThecommonthreadbehindtheMilitaryandTelcordiareliabilityanalysissystemsisdocumentingarepeatable,predictableprocessinmanufacturing.ThisisalsotheunderlyingtenetofISO9000.Bydocumentingtheprocessesusedtoproduceaproductandfollowingtheprocess,productswillbeproducedwithaconsistentlevelofquality.Thereliabilityofproductsproducedbytheseprocessescanthenberecordedandanalyzedovertimeandusedtopredictthereliabilityoffutureproducts.
Anyprocesstoproduceanyproductcanbedocumentedandserveasthebasisforreliabilityprediction.Someoftheprocessesthatareinvolvedinembeddedsystemsinclude:
systemdesign
mechanicaldesign
electronicsdesign
mechanicalfabrication
PCBdesign
mechanicalassembly
PCBfabrication
electronicsdesign
PCBassembly
softwaredesign
Thispaperwilldiscussthecomputationofreliabilityforelectronicproducts,settingupprocessesthatcanensureconsistentreliability,andtrackingandanalyzingreliabilitydata.
WhenwethinkofhighqualitydesignwemightcalltomindtheDC-3anaircraftdesignedbyDouglasin1935.TherearestillDC-3sinactivecommercialservicetoday.Infact,itisnotuncommonforaircrafttoremaininserviceformanydecades.Wemightwellask,whatmakesaircraftsoreliable?
Asubstantialpartofthatreliabilityisbasedonsoliddesign,accuratefailureanalysis,preventivemaintenance,andcontinuingmarketviability.Theseelementsbeginbeforetheproductannouncementandcontinuefarbeyondthelastactualsale.
TYPICALPRODUCTLIFECYCLE
Itwillbehelpfultounderstandatypicalproductlifecycle,todeterminewhenandhowreliabilityissuesmustbeaddressed.Figure1showsaveryhighlevelviewofProductLifeCycleforanynewproduct,beitanairplaneoranembeddedsystem.Thejobfunctionsthattypicallyparticipateinthedevelopmentandsaleofaproductareshownwiththeactivitiesgenerallyassociatedwiththosefunctionsabove.Inmanycompaniesthelinesbetweenthesejobfunctionsmaybeblurred,buttheactivitiesandresponsibilitiesareuniversal.
Theprimaryfunctionofmarketingistodetermineorgenerateamarketneedforaproduct.Themarketingjobfunctionisprimarilytoprovidetheproductconceptandtohelpvalidatethecommercialspecification.
Theroleofthesalesjobfunctionistotakethefinalproducttothemarketplaceidentifiedbyorcreatedbymarketing.Salesteamsaregenerallyinveryclosecontactwiththeclientbaseandcanservetovalidatetheproductconceptandassistinthecreationandvalidationofthecommercialspecification.
Engineering’sroleinaproductdevelopmentistotranslatetheproductconceptintoanactualproduct.Engineeringcanhaveavaluableroleindevelopingthecommercialspecificationandvalidatingthetechnicalassumptionsmadebythemarketingandsalesfunctions.
Theroleofproductmanagementistorepresentthecustomer’sinterestintheproductandtobeachampionfortheproductwithinthecompany.Productmanagementprovidesimportantinformationconcerningthevalidationofthedesignandfeedbackofinformationfromtheproductusersandpotentialusers.
Theroleofproductionis,obviouslytobuildandshiptheproduct.Productionalsoplaysavaluableroleinverifyingtheabilitytoeconomicallyproducetheproductanddetermininghowtoimprovethequalityoftheproduct.
Thediagrambelowshowstheactivitiesasflowingfromonetothenextwithoutanybacktracking.Ifthiswereusedasanactualimplementationmodeltheresultingproductisnotlikelytomeetthecustomerneeds,notlikelytobereliableandwillprobablybeshortlivedinthemarketplace.
TheremainderofthispaperwilldiscussamoredetailedviewoftheactivitiesshowninFigure1andhowtheseactivitiescanbestructuredtoensurehighreliabilityproducts.
DESIGNVERIFICATIONTESTING
Designverificationtestingistheprocessofensuringthataproductmatchesacommercialneed,canbeproducedatareasonablecost,isreliableinoperationandisconsistentwiththestrategicgoalsofthecompany.Thereisalotinthisstatementthatisunsaid,specifically,designverificationtestingisnottheprocessofensuringthatadeviceisthemostreliableorleastexpensiveorperfectmatchfortheconsumerneeds.Thesethreeareasmustbetemperedwiththestrategicgoalsofthecompany.Forexample,thereisaplaceinthemarketforthemostreliableautomobile,butthemostreliableproductmaynotbetheleastexpensivetoproduce.
Thefoundationofreliableandsuccessfulproductsisthestrategicplanforthecompany.Ifacompanyordivisionofalargercompanydoesnothaveamissionandaplantoaccomplishthatmissionitisveryunlikelythatanythingproducedbythecompanywillbeasuccess.Developingmissionsandbusinessplansarebeyondthescopeofthispaper.Itshouldberecognized,however,thatbeforebeginninganyprojecteveryoneinvolvedmustbefamiliarwiththecompanymissionandtheirpartintheplantoaccomplishthatmission.
TheprocessofDesignVerificationTestingcomprisestheactivitiesthattakeplaceintheboxeslabeled“ProductConcept”,“CommercialSpecification”,and“DetailedDesign”inFigure1.AdetailedlookatthesethreeactivitiesandhowtheyinterrelateisshowninFigure2below.
DevelopingaReliableSpecification
Themakingofahighqualityproductbeginswithahighqualitydesign.Asoliddesigndoesnotbeginwithanengineer;itbeginswiththeidentificationofasignificantmarketneedandaconceptofaproducttomeetthatneed.
Aproductconceptisusuallydevelopedbythemarketingjobfunctionwithinacompany.Theformofaproductwillbeawhitepaperorotherdocumentwiththescopeofdescribingthemarketneed,marketsize,currentsolutionsandcompetingproducts.Wewillrefertothisastheproductrequirementsdocument.Priortomovingontothenextstageofdevelopment,theCommercialSpecification,theproductrequirementsdocumentmustbevalidated.
Thereareanumberofwaystovalidatetheproductrequirementsforaproduct.Someoftheseincludefocusgroups,surveys,andinterviewswithpotentialcustomers.Theimportantissuethatthattheproductrequirementsmustbevalidatedandthatvalidationmustnotamountto
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