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ALT

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ALT

  1. 1. An introduction to HALT, HASS, HASA, and CALT Winson Mao July 2, 2012
  2. 2. Page 2 Why accelerated life testing? ► Traditional testing methods are time consuming and expensive. ► Manufacturers were not able to improve product reliability dramatically with traditional testing methods.
  3. 3. Page 3 Highly Accelerated Life Testing HALT
  4. 4. Page 4 HALT — What is it? Halt is a process to discover product design limitations by subjecting products to step stresses. • Halt is a design tool owned by engineering. • To find product defects in design stage, not to pass tests. • To stimulate defects, not to simulate environmental stresses. Different purpose Different Methods Different Equipment
  5. 5. Page 5 HALT — Equipment Example: Qualmark Typhoon 2.5 Liquid nitrogen cooled • Maximum thermal ramp rate: 200 °C/min • Temperature range: -100°C to +200°C Repetitive shock vibration • Degrees of freedom: 6 • Acceleration: over 50G Combined environment Thermal and vibration
  6. 6. Page 6 HALT — Step stress approach model Temperature step stress Vibration step stress Rapid thermal transitions Combined environment
  7. 7. Page 7 HALT — How it works? • Increase the stress, and repeat the process.
  8. 8. Page 8 HALT — Stress limits
  9. 9. Page 9 HALT — Why it works? S-N Diagram (Aluminum 7075-T6) (stress vs. number of cycles) • 40KSI 2,000,000 cycles to failure • 80KSI 2,000 cycles to failure Number of cycles Stress(KSI)
  10. 10. Page 10 HALT — Why it works? 20 15 10 5 100 200 300 400 TemperatureRateofChange°C/Min. Number of Thermal Cycles (18, 10) (10, 55) (5, 400) Rate of change vs. number of cycles 18 °C/min 10 cycles 10 °C/min 55 cycles 5 °C/min 400 cycles
  11. 11. Page 11 HALT — Summary of results Failure Percentage by Stress Type Cold Step Stress 14% Combined Environment 20% Vibration Step Stress 45% Rapid Thermal Transition 4% Hot Step Stress 17%
  12. 12. Page 12 HALT — Early fault detection is key The cost of finding and fixing a product fault:  $46 — during design phase  $228 — before procurement  $480 — before production  $22,000 — before shipment  $900,000 — on customer site ~ Hiroshi Hamada, Ricoh’s chairman
  13. 13. Page 13 HALT — BenefitsSpending Time MR MR MR — Manufacturing Release.
  14. 14. Page 14 Highly Accelerated Stress Screening HASS
  15. 15. Page 15 HASS A screening operation to detect weakness in manufacturing. • Equipment and parameters from HALT • A mixed thermal cycle/vibration stress pattern
  16. 16. Page 16 HASS — Screen profile For example
  17. 17. Page 17 HASS — General rules • Screening of 100% of production • Screening stress level — the 80/50 rule 80% of the temperature operating limits found in HALT. 50% of the vibration operating limits found in HALT. • An effective yet safe screening profile Effective: A singe application of the screen. Safe: Remove less than 5% of the total life.
  18. 18. Page 18 Highly Accelerated Stress Auditing HASA
  19. 19. Page 19 HASA The same as HASS, only operated on an audit basis instead of 100%.
  20. 20. Page 20 Calibrated Accelerated Life Testing CALT
  21. 21. Page 21 CALT — What is it? A test process that allows time compression in life testing while retaining correlation in resulting life predictions. Statistical model for CALT: • Statistic distribution The scatter in product life under a constant stress • Relationship between life and stress
  22. 22. Page 22 CALT — Failure distribution A mathematical model that describes the probability of failures occurring over time. Exponential distribution Normal distribution Lognormal distribution Weibull distribution
  23. 23. Page 23 CALT — Weibull distribution Weibull probability density ,)()( 1 et tk tf k k k     0t where k>0 is the shape parameter, λ>0 is the scale parameter. λ — the characteristic life (63.2%).
  24. 24. Page 24 CALT — Life and stress relationship Usually the mean of the life distribution is expressed as a function of the accelerating stress. • Arrhenius relationship es B CL  where s is the stress, L is the mean of the life distribution, C, B, k, n are unknown parameters. • Inverse power model s n k L   1 s BCL 1 lnln  snkL lnlnln 
  25. 25. Page 25 CALT — Approach
  26. 26. Page 26 CALT — Complications  Find the most suitable failure distribution model and life—stress relationship • Graphical data analysis • Least squares analysis • Maximum likelihood methods  Competing failure modes
  27. 27. Page 27 References  GMW8287 Highly Accelerated Life Testing, February 2002.  GMW8758 Calibrated Accelerated Life Testing (CALT), October 2004.  W. Nelson, Accelerated Testing: Statistical Methods, Test Plans, and Data Analysis, John Wiley & Sons, 2004.  H. W. Mclean, Halt, Hass, and Hasa Explained, Revised Edition, ASQ Quality Press, 2009.
  28. 28. Page 28 The End Thank you!

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