reliabilityengineering spec.docx

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