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Reliability Improvement through Step Stress
(course DEV 501)
Why Accelerated Step Stress?
- History is holding us back
- Probability estimating still dominates traditional
electronic reliability thinking
- Test to limits + determine root causes + learn
physics of failure + remove weak links => robust products
History of Environmental Stress
Testing and Screening
- 1940 - 1960 Military Handbook 217
- 1960 - 1970 Burn-in, Willis J. Willoughby's
NAVMAT P-9492
- 1980 - today AST, ESS and current best commercial
practices surpass military reliability
Failure Mechanisms and Environmental
Stress
- Components and stress stimuli
- Systems and stress stimuli
- Acceleration of electronic lifetimes; is MTBF
a valid measure of electronics life?
- Wearout modes in electronics; if not MTBF,
then what terminology to use?
Common Cause vs. Special Cause
- Common Cause Examples
- Special Cause Examples
- How HALT and HASS precipitate and detect common
and special causes
Use of Stress in Design Evaluation
and Improvement
- Benefits; limitations
- Types of Stress Stimuli
- Levels of stress
Environmental Stress Stimuli
- Thermal
- Vibration
- Combinations of stresses
Highly Accelerated Life Testing (HALT)
- How to perform a highly accelerated life test
on electronic hardware
- When to use a single stimulus and when to combine
stimuli
- How high a stress level is high enough?
- Are failures under high stress levels relevant
to field reliability?
- What equipment is needed? What personnel?
- Step stress test at what point in the design for
manufacture? At what assembly level? · What data should we gather? How
should we analyze it?"
Highly Accelerated Stress Screens
(HASS)
- Development and determination of appropriate stimuli
levels
- Proof of Screen - how test can insure we don't
damage good products
- Highly Accelerated Stress Audits (HASA)
- Examples of electronic system HASS processes
Concerns and long term improvements
in HALT and HASS
- When do we stop screening?
- How do we optimize our screen?
- Optimizing the vibration and thermal fixturing
- Feedback from screening and long-term process
improvement
Other Beneficial uses of Environmental
Step Stress
- Benchmarking suppliers - use step stress to select
most reliable components
- Benchmarking competitors - use step stress to
evaluate their quality and robustness
- Use stress to precipitate and detect intermittent
defects in NDF (No Defects Found) boards
Summary and conclusion
Award of certificate
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