![2
NTSB chairman Deborah Hersman
“The design and certification assessment and the assumptions
that were made were not born out by what we saw,” …speaking
about the battery fires in Boston and Japan. “We had two events
in two weeks on two separate aircraft. The fleet has less than
100,000 hours and [Boeing] did not expect in their assessment to
see a smoke event in but less than 1 in every 10,000,000 hours.”
From NTSB
Website
From NTSB
Website](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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CTEA Test Symposium Presentation: Overview of HALT and HASS: A Major Paradigm Shift
- 1. Overview of HALT and HASS: A Paradigm Shift in Reliability Testing Kirk Gray, Principal Consultant Accelerated Reliability Solutions, L.L.C. Email: kirk@acceleratedreliabilitysolutions.com Phone: 512-554-3111 Central Texas Electronics Association Electronics Design, Manufacturing & Test Symposium
- 2. 2 NTSB chairman Deborah Hersman “The design and certification assessment and the assumptions that were made were not born out by what we saw,” …speaking about the battery fires in Boston and Japan. “We had two events in two weeks on two separate aircraft. The fleet has less than 100,000 hours and [Boeing] did not expect in their assessment to see a smoke event in but less than 1 in every 10,000,000 hours.” From NTSB Website From NTSB Website
- 3. 3 The U.S. Food and Drug Administration today issued a proposed order aimed at helping manufacturers improve the quality and reliability of automated external defibrillators FDA has received approximately 45,000 adverse event reports between 2005 and 2012 associated with the failure of these devices
- 5. Fundamental mismatch of time scales 5 Wear out IS NOT a significant cause of un-reliability for vast majority of (non-mechanical) electronics assemblies Hazard rate Time 7 to 30 years? Technology Obsolescence Wear out Use period 5-7 years The Life Cycle Bathtub Curve
- 6. Costs and Reliability Development 6 Most of the costs of unreliability occur in the first several months or years Hazard rate Time 7 to 15 years? Technology Obsolescence $$$$$ Warranty Returns Perception of poor quality Lost future sales! Prediction-Modeling of wear out
- 7. There is a Drain in the Bathtub Curve 7 $$$ $$$ $??? (ex. Power generation systems)
- 8. Basis for HALT 8 A chain is only as strong as its weakest link.
- 9. Fundamental Basis for HALT 9 Fastest way to find a weak link is find the strength and stress limit… Pull until it breaks
- 10. HALT 10 HALT – Highly Accelerated Life Test Controlled Stepped Stress test to empirical operational and sometimes destruct limits A methodology and significant reliability paradigm shift – not a type of stress or type of chamber A discovery process, - a Stimulation not a Simulation process
- 11. The Base HALT process Continue until operating & destruct limits of UUT are found or until test equipment limits are reached. Level of Applied Stress Stimuli (vibration or thermal) Time (hour:minute) Step A Step B Step C Step D 0:00 0:10 0:20 0:30 Thermal Steps: typically +10ºC and -10ºC Vibration steps: typically 5-10 Grms cold 11
- 12. The Base HALT process Continue until operating & destruct limits of UUT are found or until test equipment limits are reached. Level of Applied Stress Stimuli (vibration or thermal) Time (hour:minute) Step A Step B Step C Step D 0:00 0:10 0:20 0:30 Thermal Steps: typically +10ºC and -10ºC Vibration steps: typically 5-10 Grms Heat 12
- 13. The Base HALT process Continue until operating & destruct limits of UUT are found or until test equipment limits are reached. Level of Applied Stress Stimuli (vibration or thermal) Time (hour:minute) Step A Step B Step C Step D 0:00 0:10 0:20 0:30 Thermal Steps: typically +10ºC and -10ºC Vibration steps: typically 5-10 Grms vibration 13 After finding limits with each single stress, try thermal cycling, combinations of stress
- 14. Outputs of HALT 14 1) List of potential failure mechanisms, weaknesses and the relevance to field failures. 2) Opportunity to increase reliability “tolerance” at lowest costs when done early. 3) Safe limits and stress boundaries to create a cost effective HASS processes.
- 15. HALT IS 15 Deterministic- find weak links by stressing to inherent limits Based on fundamental limits (strength) of standard electronics and - not end-use environmental conditions Done while products are powered and functionally monitored during stress application Not a quantifiable “life” test - no stress test for systems can accelerate all fatigue or chemical degradation mechanisms at equivalent field rates
- 16. Common Responses to HALT Discoveries 16 “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 we would have designed it for those conditions” Why many companies claiming to do “HALT” only do the first part – find limits but do nothing to improve them
- 17. HALT/HASS IS NOT to develop products to survive extreme conditions or environments 17
- 18. HALT vs. HASS Stress Levels 18 Stress Level (example temperature) UpperDesignSpec UpperOperatingLimit UpperStrengthLimit LowerDesignSpec LowerOperatingLimit LowerStrengthLimit(rare) HALT HASS TypicalUse
- 19. Level of Applied Stress Stimuli Time (hour:minute) Upper operation thermal limit Lower Operation thermal Limit 0:00 0:10 0:20 0:30 Vibration level vib temperature Temperature 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 Parameters 19 Vibration level UDL
- 20. The Stress Strength Model 20 In 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 occur Stress/Strength Load Strength # of field units
- 21. The Stress Strength Model 21 For multiple units - results distribution around the nominal values Variations in end-use stresses for the most part are uncontrolled Variations in assembly strength Also applies to thermal and electrical stress/strength Stress Strength Load= cumulative fatigue from use Strength= assembly fatigue strength # of field units High Fatigue Low Fatigue Low Strength High strength
- 22. Stress/Strength Diagram and Failures 22 If Stress < Strength, no failures occur As fatigue damage (aging) accumulates, the mean of the strength shifts left Field failures occur when the two distributions overlap - the weakest units are subjected to the highest life cycle stresses Stress Strength cumulative fatigue damage # of units Strength Low Fatigue High Fatigue High strength Low Strength
- 23. Stress/Strength Diagram and Failures 23 If Stress < Strength, no failures occur As fatigue damage (aging) accumulates, the mean of the strength shifts left Field failures occur when the two distributions overlap - the weakest units are subjected to the highest life cycle stresses Stress Strength cumulative fatigue damage # of units Field Failures Strength Low Fatigue High Fatigue
- 24. Develop Tolerance of Variations 24 New 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 determining if and how the margin can be improved Small changes can result in large margin gains Stress Strength #offieldunits Greatest tolerance for Manufacturing variationMaximize Functional margin =
- 25. Thermal Stress to Skew Parametrics 25 Marginal designs may not be observable until a sufficient number of units are in the field The field is a costly place to find these marginal conditions Parametric timing value Parametric timing value #units #units 100 100,000 Limited samples During development Mass Production variation Parameter Specification Lower op limit Upper op limit Lower op limit Upper op limit Parameter Specification Marginal operation regions 1,000
- 26. Timing Skewing from Thermal Stress 26 Applying thermal stress stimulates a timing shift Parametric timing value units 100 Parameter Specification Lower op limit Upper op limit Cold • Thermal Step Stress and cycling provides a much higher probability of detecting low incidence rate issues • Cold speeds up signal propagation
- 27. Timing Skewing from Thermal Stress 27 Applying thermal stress stimulates a timing shift Parametric timing value units 100 Parameter Specification Lower op limit Upper op limit HOT • Thermal Step Stress and cycling provides a much higher probability of detecting low incidence rate issues • Heat slows down signal propagation
- 28. Power supply HALT and HASS Success 28 A worldwide leader in the development and marketing of power conversion and control system solutions was looking for methods to reduce warranty returns. The Company makes power supplies and subsystems used in Capital Equipment for thin film applications
- 29. Company’s First HALT and HASS Results 29 Results after HALT To HASS on the a shipping power supply unit (6KW) DC production Manufacturing testing for reliability cycle time was reduced from 4 days of “burn-in” to a HASS process lasting 40 minutes per 2 units. Warranty returns were reduced 90% - from 5.0% to 0.5% - within months after introduction of design change and HASS
- 30. 21st Century path to optimizing electronics reliability 30 Design using good design practices and lessons learned Test to empirical operational limits and sometimes destruct 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 shortest screening (HASS/HASA) processes Improve screens - Find best discriminators to observe failures in manufacturing capability or process control
- 31. 31 Relevant Quote “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it” -Max Planck, Scientific Autobiography
Editor's Notes
- Modeling can be useful and an important tool for LIMITED applications – such a Finite Element Analysis – especially in mechanical wear, hinges, bearings, Single BGA – but many if not most have more than one stress driverComponent failure doesn’t always result in systems failure ….Mention the 26 capacitors in a system that was defective but only 5 locations cause hard failures of the system…Variation of manufacturing quality, excursions, and errors or abuse are the cause of the vast majority of failures before technological obsolesence
- Modeling can be useful and an important tool for LIMITED applications – such a Finite Element Analysis – especially in mechanical wear, hinges, bearings, Single BGA – but many if not most have more than one stress driverComponent failure doesn’t always result in systems failure ….Mention the 26 capacitors in a system that was defective but only 5 locations cause hard failures of the system…Variation of manufacturing quality, excursions, and errors or abuse are the cause of the vast majority of failures before technological obsolesence
- Old AdageChain is only as strong as weakest LengthElectronics systems are only as robust as the weakest componentLike a chain – most electronics systems have significant strength - won’t know until you find the limit – In thermal its mostly OPERATIONAL LIMITS ONLY – no need to go beyond operation - dangerous If limits are found, you can use the “stress Capability” as a benchmark of materials and system strength to test underNot testing beyond Spec – may not find “weak link” before it’s a field reliability problem
- Old AdageChain is only as strong as weakest LengthElectronics systems are only as robust as the weakest componentLike a chain – most electronics systems have significant strength - won’t know until you find the limit – In thermal its mostly OPERATIONAL LIMITS ONLY – no need to go beyond operation - dangerous If limits are found, you can use the “stress Capability” as a benchmark of materials and system strength to test underNot testing beyond Spec – may not find “weak link” before it’s a field reliability problem
- Since we know that thermal stimulation can skew the timing,We also know that there will be SOME variation in the timing parametrics of critical components in quantity production – how much will it vary in the future or if a second source of that component is Substituted during the systems production life
- The challenge in development is that the component and assembly variations will occur throughout the production life of the productWe probably do not know the how wide these variations might be and how they will affect our producthopefully occur in a small percentage of the population – 1 to 3%The probability of seeing these failures with 10 – 20 samples is very LOW We can help see these potential reliability risks when we use thermal stress to skew the silicon
- The challenge in development is that the component and assembly variations will occur throughout the production life of the productWe probably do not know the how wide these variations might be and how they will affect our producthopefully occur in a small percentage of the population – 1 to 3%The probability of seeing these failures with 10 – 20 samples is very LOW We can help see these potential reliability risks when we use thermal stress to skew the silicon