Reliability Improvement through Step Stress
(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
