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Overview of halt a paradigm shift for rev3

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Overview of halt a paradigm shift for rev3

  1. 1. Overview of HALT and HASS: AParadigm Shift in Reliability TestingKirk Gray, Principal ConsultantAccelerated Reliability Solutions, L.L.C.Email: kirk@acceleratedreliabilitysolutions.comPhone: 512-554-3111Central Texas Electronics AssociationElectronics Design, Manufacturing & Test Symposium
  2. 2. 2NTSB chairman Deborah Hersman“The design and certification assessment and the assumptionsthat were made were not born out by what we saw,” …speakingabout the battery fires in Boston and Japan. “We had two eventsin two weeks on two separate aircraft. The fleet has less than100,000 hours and [Boeing] did not expect in their assessment tosee a smoke event in but less than 1 in every 10,000,000 hours.”From NTSBWebsiteFrom NTSBWebsite
  3. 3. 3The U.S. Food and Drug Administration todayissued a proposed order aimed at helpingmanufacturers improve the quality and reliabilityof automated external defibrillatorsFDA has received approximately 45,000 adverseevent reports between 2005 and 2012 associatedwith the failure of these devices
  4. 4. 4Electronics Reliability Prediction
  5. 5. Fundamental mismatch of time scales5Wear out IS NOT a significant cause of un-reliability forvast majority of (non-mechanical) electronicsassembliesHazard rateTime7 to 30 years?TechnologyObsolescenceWear outUse period 5-7 yearsThe Life Cycle Bathtub Curve
  6. 6. Costs and Reliability Development6Most of the costs of unreliability occur in the firstseveral months or yearsHazard rateTime7 to 15 years?TechnologyObsolescence$$$$$Warranty ReturnsPerception of poor qualityLost future sales!Prediction-Modelingof wear out
  7. 7. There is a Drain in the Bathtub Curve7$$$$$$ $???(ex. Powergeneration systems)
  8. 8. Basis for HALT8A chain is only as strong as its weakestlink.
  9. 9. Fundamental Basis for HALT9Fastest way to find a weak link is find thestrength and stress limit…Pull until it breaks
  10. 10. HALT10 HALT – Highly Accelerated Life Test Controlled Stepped Stress test to empiricaloperational and sometimes destruct limits A methodology and significant reliabilityparadigm shift – not a type of stress or type ofchamber A discovery process, - a Stimulation not aSimulation process
  11. 11. The Base HALT processContinue until operating & destruct limitsof UUT are found or until test equipmentlimits are reached.Level of Applied Stress Stimuli(vibration or thermal)Time (hour:minute)Step AStep BStep CStep D0:00 0:10 0:20 0:30Thermal Steps: typically +10ºC and -10ºCVibration steps: typically 5-10 Grmscold11
  12. 12. The Base HALT processContinue until operating & destruct limitsof UUT are found or until test equipmentlimits are reached.Level of Applied Stress Stimuli(vibration or thermal)Time (hour:minute)Step AStep BStep CStep D0:00 0:10 0:20 0:30Thermal Steps: typically +10ºC and -10ºCVibration steps: typically 5-10 GrmsHeat12
  13. 13. The Base HALT processContinue until operating & destruct limitsof UUT are found or until test equipmentlimits are reached.Level of Applied Stress Stimuli(vibration or thermal)Time (hour:minute)Step AStep BStep CStep D0:00 0:10 0:20 0:30Thermal Steps: typically +10ºC and -10ºCVibration steps: typically 5-10 Grmsvibration13After finding limits with each single stress, try thermalcycling, combinations of stress
  14. 14. Outputs of HALT141) List of potential failure mechanisms, weaknessesand the relevance to field failures.2) Opportunity to increase reliability “tolerance” atlowest costs when done early.3) Safe limits and stress boundaries to create a costeffective HASS processes.
  15. 15. HALT IS15 Deterministic- find weak links by stressing to inherent limits Based on fundamental limits (strength) of standard electronicsand - not end-use environmental conditions Done while products are powered and functionally monitoredduring stress application Not a quantifiable “life” test - no stress test for systems canaccelerate all fatigue or chemical degradation mechanisms atequivalent field rates
  16. 16. Common Responses to HALT Discoveries16 “Of course it failed, you took it above specifications” “It will never see that stress level in use” “It wasn’t designed for that vibration level” “If you wanted it to operate in those conditions wewould have designed it for those conditions”Why many companies claiming to do “HALT” only dothe first part – find limits but do nothing to improvethem
  17. 17. HALT/HASSIS NOT to develop products to survive extremeconditions or environments17
  18. 18. HALT vs. HASS Stress Levels18Stress Level(example temperature)UpperDesignSpecUpperOperatingLimitUpperStrengthLimitLowerDesignSpecLowerOperatingLimitLowerStrengthLimit(rare)HALTHASSTypicalUse
  19. 19. Level of AppliedStress StimuliTime (hour:minute)Upper operationthermal limitLowerOperationthermal Limit0:00 0:10 0:20 0:30Vibration levelvibtemperatureTemperature level• Rapid thermal cycling (up to 60ºC/minute) – two to five thermal cycles• Combined with multi-axis vibration – vary intensity during application• Other stresses (power cycling, voltage margining, frequency margining)HASS and HASA Process Parameters19Vibration levelUDL
  20. 20. The Stress Strength Model20In assemblies and structures there is a loadLoad = cumulative life-cycle fatigue (aging) from normal useStrength = the material fatigue life of electronic materialsAs Long as Load < Strength no failures occurStress/StrengthLoad Strength# of field units
  21. 21. The Stress Strength Model21 For multiple units - results distribution around thenominal valuesVariations in end-use stresses for the most part are uncontrolledVariations in assembly strengthAlso applies to thermal and electrical stress/strengthStress StrengthLoad= cumulativefatigue from useStrength= assemblyfatigue strength# of field unitsHighFatigueLowFatigue LowStrengthHighstrength
  22. 22. Stress/Strength Diagram and Failures22If Stress < Strength, no failures occur As fatigue damage (aging) accumulates, the mean ofthe strength shifts left Field failures occur when the two distributions overlap -the weakest units are subjected to the highest life cyclestressesStress Strengthcumulativefatiguedamage# of unitsStrengthLowFatigueHighFatigueHighstrengthLowStrength
  23. 23. Stress/Strength Diagram and Failures23If Stress < Strength, no failures occur As fatigue damage (aging) accumulates, the mean ofthe strength shifts left Field failures occur when the two distributions overlap -the weakest units are subjected to the highest life cyclestressesStress Strengthcumulativefatiguedamage# of unitsFieldFailures StrengthLowFatigueHighFatigue
  24. 24. Develop Tolerance of Variations24New Path to Optimal Reliability: Find the functional margins by testing to absolute operational limits(thermal OTP defeated) Improve margins by finding the limiting component(s) and determiningif and how the margin can be improved Small changes can result in large margin gainsStress Strength#offieldunitsGreatest tolerance forManufacturing variationMaximize Functional margin=
  25. 25. Thermal Stress to Skew Parametrics25 Marginal designs may not be observable until asufficient number of units are in the field The field is a costly place to find these marginalconditionsParametrictiming valueParametric timingvalue#units#units100 100,000Limited samples During development Mass Production variationParameterSpecificationLower oplimitUpper oplimitLower oplimitUpper oplimitParameterSpecificationMarginaloperationregions1,000
  26. 26. Timing Skewing from Thermal Stress26Applying thermal stress stimulates a timing shiftParametrictiming valueunits100ParameterSpecificationLower oplimitUpper oplimitCold• Thermal Step Stress and cycling provides a muchhigher probability of detecting low incidence rate issues• Cold speeds up signal propagation
  27. 27. Timing Skewing from Thermal Stress27Applying thermal stress stimulates a timing shiftParametrictiming valueunits100ParameterSpecificationLower oplimitUpper oplimitHOT• Thermal Step Stress and cycling provides a muchhigher probability of detecting low incidence rate issues• Heat slows down signal propagation
  28. 28. Power supply HALT and HASS Success28A worldwide leader in the development andmarketing of power conversion and controlsystem solutions was looking for methods toreduce warranty returns.The Company makes power supplies andsubsystems used in Capital Equipment for thin filmapplications
  29. 29. Company’s First HALT and HASS Results29Results after HALT To HASS on the a shipping powersupply unit (6KW) DC production Manufacturing testing for reliability cycle time wasreduced from 4 days of “burn-in” to a HASSprocess lasting 40 minutes per 2 units. Warranty returns were reduced 90% - from 5.0% to0.5% - within months after introduction of designchange and HASS
  30. 30. 21st Century path to optimizingelectronics reliability30 Design using good design practices and lessons learned Test to empirical operational limits and sometimesdestruct Determine root causes of limits Understand the physics of failure or limit Remove or improve weak links – to make robust products Apply combined safe stresses to make shortestscreening (HASS/HASA) processes Improve screens - Find best discriminators to observefailures in manufacturing capability or process control
  31. 31. 31Relevant Quote“A new scientific truth does not triumph byconvincing its opponents and makingthem see the light, but rather because itsopponents eventually die, and a newgeneration grows up that is familiar withit”-Max Planck, Scientific Autobiography

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