HALT and HASS

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1、PitfallstoAvoidinHALTandHASSGreggK.Hobbs,Ph.D.,P.E.MuchhasbeenwrittenonwhattodoinHALTandHASS.Whatnottodoshouldalsobediscussedinordertoenforcethepositive.Someofthemostcommonlyoccurringmistakeswillbediscussedanditwillbepointedoutwhyeachisamistake.Themistake

2、isfirststatedinboldtypeandthenisdiscussedverybriefly.Allofthesearecoveredinmoredetailinmytextbook,HALTandHASS,AcceleratedReliabilityEngineering,whichissoldthroughHobbsEngineering.NotperformingSafetyofHASS.Thisisoneoftheworstpossiblemistakesthatcanbemadean

3、dissomewhatequivalenttoplayingRussianRoulettewithseveralcylindersloaded.HighlyAcceleratedStressScreensarequitecapableofreducingtheusablefieldlifeofgoodhardwareifthestressesarechosentobetoohighforthedesignandprocessesunderwhichitisbuilt.IfHALThasbeenproper

4、lydone,thenthisrarelyoccurs.IfHALThasnotbeendoneatallorifthemarginsattainedarenothighenough,thenfieldlifereductionmayoccur.TheonlywaytoreasonablyprovethatthescreensaresafetouseinproductionistorunSafetyofHASS.Ifthisisnotdone,thenthefieldfailureswilldetermi

5、neiftheHASShasbeenproperornot.Clearly,thiswaitandseeapproachisnotagoodwaytofindoutifthescreensaretoointenseas,bythetimeitisrecognizedthatthescreensaretoointense,substantialnumbersofreducedlifeunitswillhavebeenshipped.SafetyofHASSismandatoryforpropertechni

6、que.Notmonitoringwithhighcoverageduringstimulation.Thisisalsooneoftheworstpossiblemistakesthatcanbemadeandusuallyleadstoasubstantialfinancialloss.Whatwillusuallyhappeninthissituationisthatflawswillbeprecipitatedbutnotdetectedandthenthecustomerwillhavefail

7、uresduetoprecipitateddefectssoonafterdeliveryleadingtoaveryunhappycustomerandmanyfieldreturns.Itissuggestedthatifonecannotmonitortheproducttoatleastamodestextentduringstimulationwiththevariousstresses,thewholeideaofHALTandHASSshouldjustbeabandoned.HALTand

8、HASS(aswellasclassicalscreeningandtesting)withoutgoodcoveragearelessthanworthless!CoveragecanbedeterminedandimprovedsignificantlybyperformingSoftwareTMHALT.Notusingacceleratedstressconditions.Ifacceleratedstresscond