22-A118 加速湿气无偏压抵抗HAST

JEDEC

STANDARD

AcceleratedMoistureResistance-

UnbiasedHAST

JESD22-A118

DECEMBER2000

JEDECSOLIDSTATETECHNOLOGYASSOCIATION

JEDECStandandNo.22-A118

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ACCELERATEDMOISTURERESISTANCE-UNBIASEDHAST

(FromJEDECBoardBallotJCB-00-56,formulatedunderthecognizanceoftheJC-14.1

SubcommitteeonReliabilityTestMethodsforPackagedDevices.)

1Purpose

TheUnbiasedHASTisperformedforthepurposeofevaluatingthereliabilityofnon-hermetic

packagedsolid-statedevicesinhumidenvironments.Itisahighlyacceleratedtestwhich

employstemperatureandhumidityundernon-condensingconditionstoacceleratethepenetration

ofmoisturethroughtheexternalprotectivematerial(encapsulantorseal)oralongtheinterface

betweentheexternalprotectivematerialandthemetallicconductorswhichpassthroughit.Bias

isnotappliedinthistesttoensurethefailuremechanismspotentiallyovershadowedbybiascan

beuncovered(e.g.galvaniccorrosion).Thistestisisusedtoidentifyfailuremechanismsinternal

tothepackageandisdestructive.

2Scope

Thistestmethodappliesprimarilytomoistureresistanceevaluationsandrobustnesstesting,and

maybeusedasanalternativetounbiasedautoclave.Samplesaresubjectedtoanon-condensing,

humidatmosphere,similartotheJESD-22-A101,"SteadyStateTemperature,HumidityandBias

LifeTest",butwithahighertemperature.Forthetemperaturelimitsdefinedbythisprocedure,

thetestwilltypicallygeneratethesamefailuremechanismsasthoseinanunbiased

"85°C/85%RH"SteadyStateHumidityLifeTest,butcautionmustbeusedifhigher

temperaturesareconsideredsincenon-realisticfailuremodescanbegenerated.Theuseofa

non-condensingenvironmentavoidsmanyirrelevantexternalfailures,e.g.,pin-to-pinleakageor

leadcorrosion.However,becauseabsorbedmoisturetypicallydecreasesglasstransition

temperatureformostpolymericmaterials,thecombinationofhighhumidityandhigh

temperature(>T)mayproduceunrealisticmaterialfailures.Thus,cautionisneededifand

whenUnbiasedHASTisrequiredforreliabilityorqualificationpurposes.

g

3Apparatus

Thetestrequiresapressurechambercapableofmaintainingaspecifiedtemperatureandrelative

humidityduringramp-upto,andramp-downfrom,thespecifiedtestconditions.

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3Apparatus(cont’d)

3.1Records

Apermanentrecordofthetemperatureprofileforeachtestcycleisrecommended,sothestress

conditionscanbeverified.Calibrationrecordsshallverifythattheequipmentavoids

condensationondevicesundertest(DUTs)hotterthan50°Cduringramp-upandramp-downfor

conditionsofmaximumthermalmassloading.Calibrationrecordsshallverifythat,forsteady

stateconditionsandmaximumthermalmassloading,testconditionsaremaintainedwithinthe

tolerancesspecifiedin3.1.

3.2DevicesUnderStress

Devicesunderstressmustbeplacedinthechambertominimizetemperaturegradients.Devices

understressshallbenocloserthan3cmfrominternalchambersurfaces,andmustnotbe

subjectedtodirectradiantheatfromheaters.Ifdevicesaremountedonboards,theboards

shouldbeorientedtominimizeinterferencewithvaporcirculation.

3.3IonicContamination

Caremustbeexercisedinthechoiceofanymaterialsintroducedintothechamberinorderto

minimizereleaseofcontamination,andminimizedegradationduetocorrosionandother

mechanisms.Ioniccontaminationofthetestapparatusshallbecontrolledtoavoidtestartifacts.

3.4DistilledorDeionizedWater

Distilledordeionizedwaterwithaminimumresistivityof1megohm-cmatroomtemperature

shallbeused.

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4Testconditions

Testconditionsconsistofatemperature,relativehumidity,andduration.

Table1—Temperature,relativehumidityandpressure

Test

condition3,4

Relative

(drybulb°C)humidity1(%)(wetbulb,°C)

Temperature2Vaporpressure2

(psia/kPa)

33.3/230

17.7/122

A

B

130±2

110±2

85±5

85±5

124.7

105.2

NOTES

1Tolerancesapplytotheentireusabletestarea.

2Forinformationonly.

3Thetestconditionsaretobeappliedcontinuouslyexceptduringanyinterimreadouts.Forinterim

readouts,devicesshouldbereturnedtostresswithinthetimespecifiedin5.4

4TheunbiasedHASTdurationisintendedtomeetorexceedanequivalentfieldlifetimeunderuse

conditions.Thedurationisestablishedbasedontheaccelerationofthestress(seeJEP122).Thestress

durationisspecifiedbyinternalqualificationrequirements,JESD47ortheapplicableprocurement

document.Typicaltestdurationsare:

Condition

Duration

96hours(-0,+2)

264hours(-0,+2).

A

B

CAUTION:Forplastic-encapsulatedmicrocircuits,itisknownthatmoisturereducestheeffectiveglass

transitiontemperatureofthemoldingcompound.Stresstemperaturesabovetheeffectiveglasstransition

temperaturemayleadtofailuremechanismsunrelatedtooperationaluse.

5Procedure

Thetestdevicesshallbemountedinamannerthatexposesthemtoaspecifiedconditionof

temperatureandhumidity.Exposureofdevicestoconditionsthatresultincondensationon

them,particularlyduringramp-upandramp-down,shallbeavoided.Whiledevicesareabove

30oC,R.H.mustbe≥40%toensuretheirmoisturecontentisnotreduced,i.e.,inadvertant

moisturebakeout.

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5Procedure(cont’d)

5.1Ramp-up

5.1.1Thetimetoreachstabletemperatureandrelativehumidityconditionsshallbelessthan3

hours.

5.1.2Condensationshallbeavoidedbyensuringthatthetestchamber(drybulb)temperature

exceedsthewet-bulbtemperatureatalltimes,andthattherateoframpupshallnotbefasterthan

aratewhichensuresthatthetemperatureofanyDUTdoesnotlagbelowthewetbulb

temperature.

5.1.3Thedry-andwet-bulbtemperaturesetpointsshallbemaintainedsothattherelative

humidityisnotlessthan50%aftersignificantheatingbegins.Inadrylaboratory,thechamber

ambientmayinitiallybedrierthanthis.

5.2Ramp-down

5.2.1Thefirstpartoframp-downtoaslightlypositivegaugepressure(awetbulbtemperature

ofabout104°C)shallbelongenoughtoavoidtestartifactsduetorapiddepressurization,but

shallnotexceed3hours.

5.2.2Thesecondpartoframp-downfromawetbulbtemperatureof104°Ctoroomtemperature

shalloccurwiththechambervented.Thereisnotimerestriction,andforcedcoolingofthe

vesselispermitted.

5.2.3Condensationondevicesshallbeavoidedinbothpartsoftherampdownbyensuringthat

thetestchamber(drybulb)temperatureexceedsthewet-bulbtemperatureatalltimes.

5.2.4Ramp-downshouldmaintainthemoisturecontentofthemoldingcompoundencapsulating

thedie.Therefore,therelativehumidityshallnotbelessthan50%duringthefirstpartofthe

ramp-down,see5.2.1.

5.3TestClock

Thetestclockstartswhenthetemperatureandrelativehumidityreachthesetpoints,andstopsat

thebeginningoframp-down.

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5Procedure(cont’d)

5.4Readout

Electricaltestshallbeperformednotlaterthan48hoursaftertheendoframp-down.Note:For

intermediatereadouts,devicesshallbereturnedtostresswithin96hoursoftheendoframp-

down.Therateofmoisturelossfromdevicesafterremovalfromthechambercanbereducedby

placingthedevicesinsealedmoisturebarrierbags,thebagsshouldbenon-vacuumsealed

withoutaN2purgeandwithoutdessicant.Whendevicesareplacedinsealedbags,the"test

windowclock"runsat1/3oftherateofdevicesexposedtothelaboratoryambient.Thusthe