Mean Time Between Failure (MTBF) is the average time between the failures of pieces of a given product.

1. 3/6/23, 3:01 PM MTBF: Concept and Application - Oxeltech
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MTBF: Concept And Application
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MTBF As A Failure Time Frequency
Prediction Criteria
From playgadgetstoprofessional machines,itisrelevantfor theproductsellersaswell as
regulatoryauthoritiesandconsumerstoknowtheprobabilityof failuresexpectedin the
lifetimeof thedevice.In electronics,onemetricoften usedtoestimatedeviceperformance
over itslifetimeisMTBF.
Mean TimeBetween Failure(MTBF)istheaveragetimebetween thefailuresof piecesof a
given product.
TheMTBFof adeviceanditsfailureratehavean inverserelationship:
MTBF=1/λ
Theunitsin thiscasearehoursor lifecycles.Italsoallowsfor thecalculation of oneof the
other quantityisknown.For thisparticular analysis,theconventional bath-tubcurveisused,
specificallythecentral partof thecurve.
In thispart,thedevicehaspassedtheinitial failurerisksandtherateatwhich devicesfail
becomesrelativelyconstant.Assumingaconstantfailurerate,theprobabilitythatadevice
will workfor aspecificamountof timecan befoundbyusingthefollowingrelation:
Tableof Content
• MTBF asaFailureTimeFrequencyPredictionCriteria
•MIL-HDBK-217FStandard
•Reliability Prediction Methods in MIL-HDBK-217FStandard
•MIL-217-F (Part Count Method)
•MIL-217-F (Part Stress Analysis Method)
•SoftwareSolutions forFailureRateand MTBFCalculation
• Useful Links
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Survival Probability of aDevice =e
Heretisthetimein hoursfor which thesurvival probabilityof adeviceistobefoundandMBTF
isthecumulativevalueof theindividual MTBFvaluesof thecomponentsusedin thedevice.
MTBFvalueprediction isacrucial partof productdesign andisusedbyreliabilityengineers
anddesignersatdifferentstagesof thedesign process.Therearevariousstandardsin place
for implementingMTBFprediction andtheir selection isbasedon theparticular design stage.
ThesestandardsandmethodsincludeMIL-HDBK-217F,TelcordiaSR332,SiemensNorm,
FIDES,andUTE80-810 (RDF2000),etc.For thepurposeof thisdocument,MIL-HDBK-217Fis
discussedandtwoof itsmajor prediction methodsareexplainedbriefly.
MIL-HDBK-217F Standard
MIL-217Fisastandardthatprovidesfailurerateprediction modelsfor electrical and
mechanical componentcategories.All of thisinformation relatedtotheMIL-217Fstandardis
given in theMIL-HDBK-217FhandbookpublishedbytheUnitedStatesDepartmentof Defense.
Therearetwomethodsthatarelistedunder thisstandardi.e.PartCountMethodandPart
StressAnalysisMethod.
Reliability Prediction Methods In MIL-HDBK-217F
Standard
MIL-217-F (Part Count Method)
In thisprediction method,thequantityof parts,qualityfactor andenvironmentsettingsand
makeafailurerateprediction.
Asitfactorsin veryfewvariables,itsapplication islimitedtotheearlystagesof thedesign
when theproductisbeingproposed.Therelation thatisusedfor calculation isgiven here:
λ =Σ N . λ . Π
Heren isthetotal number of categories,N isthenumber of i part,λ isthefailurerateof the
i componentandΠ isthequalityfactor.Thisrelation equalstoλwhich representsthetotal
failurerateof thedevice.
-t/MTBF
i=1 ton i i Qi
i
th
i
th
Qi
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MIL-217-F (Part Stress Analysis Method)
AscomparedtothePartCountmethod,thePartStressAnalysismethodincludesmore
factorsascomparedtothepartcountmethod.
Thismakesthisamuch moreaccuratemeasureof failurerate.Themodel usedfor thepart
stressanalysismethodfor microelectroniccircuitsandmemoriesisshown here:
λ =(C Π +C Π +λ ). Π Π
In thismodel,C isthefailurerateof diecomplexity,Π isthetemperaturefactor,C isthe
failurerateof thepackage,Π istheenvironmentfactor,λ isthefailurerateinducedby
Read/Writecycles,Π isthequalityfactor andΠ isthelearningfactor.
Software Solutions For Failure Rate And MTBF
Calculation
In addition tothemanual failureratecalculation byusingtheMIL-HDBK-217Fstandard
handbook,therearesoftwaretoolsaswell thatareavailableonlinefor free.Oneof the
simplesttoolsthatcan beusedfor failureratevaluecalculation isprovidedbyALD services.
Thesoftwaresupportsboth thepartcountmethodandthepartstressanalysismethod.This
can beillustratedbythefigurebelowin which themain windowisshown:
MTBFCalculatorMainWindow
Asobservedin thefigure,both variantsof MIL-217Fi.e.partcountandpartstressanalysis,are
available.Todevelopacomparison between thedetailsusedin both methods,their
correspondingdialogueboxescan becompared.Hereisthesnapshotof thedialogueboxfor
p 1 T 2 E cyc Q L
1 T 2
E cyc
Q L
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thepartcountmethodfor acapacitor in which themain factorsarequantity,partnumber,
andstyle,etc.
DialogueBoxforPartCountMethod
In contrasttothepartcountmethod,thepartstressanalysistakesintoaccountquantity,
partnumber,style,value,ratedandappliedvoltage,quality,termination styleandin-circuit
resistanceetc.Thiscan beclearlyvisualizedin thefollowingsnapshot:
DialogueBoxforPartStressAnalysisMethod
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Thesoftwarecan bedownloadedfrom thelink[1] given in the‘Useful Links’ section and
further explored.Furthermore,another MTBFcalculator availableatDigikey’swebsitecan
alsobeusedfor failureratecalculation.
Toconclude,wehavelookedatthecoreideabehindtheterms‘’Mean Timebetween Failures’
andfailurerates,andthemethodsusedtocalculatethem.Wehavealsocoveredonlinetools
thatcan beutilizedtocalculatethesequantities.
Useful Links
1.MTBF-Calculator (https://aldservice.com/Free-MTBF-Calculator.html)
2.BQRon-lineapplication (https://www.digikey.de/en/resources/design-tools/bqr-on-
line-application)
If you are facing any difficulties with your MTBFAnalysis, or other Reliability Analysis of
your design or product, or any design-related challenge in general, feel free to Contact
Us (https://oxeltech.de/en/contact-us/)for our consultancy. You can check out our
other Technical Blogs (https://oxeltech.de/en/blog/)on various topics or visit our new
website Oxeltech.de to find all about our services (https://oxeltech.de/en/services/)
and products.
Team Oxeltech
 October 6, 2022(https://oxeltech.de/en/2022/10/06/)
 7:08 am
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