Basics of Accelerated Reliability Improvement through Empirical Stress Boundary and Limit Testing
Why Accelerated Step Stress?
Reliability Prediction is a misleading approach – failures in electronics systems can be phenomenologically complex, chaning processes and materials make a moving target for models.
Many mechanisms and variability in manufacturing and end-use life cycle stress
Test to Limits + determine root causes + learn the physics of failure remove weak links - create robust products
History of Reliability Engineering and Environmental Stress Testing and Screening
1950 - 1970 Military Handbook 217
1970 -1980 Burn-in, Willis J. Willoughby's NAVMAT P-9492
1980 's- today, AST and ESS - and current best commercial practices
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?
Use of Stress in Design Evaluation and Improvement
Types of Stress Stimuli
Levels of stress
Environmental Stress Stimuli
Thermal - how it helps in stimulation of marginal software/firmware to find operational reliability issues
Vibration - ED versus Repetitive Shock Systems
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 level of stress is high enough?
Are failures under high levels of stress 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 systems 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 more reliable components
Benchmarking Competitors - use step stress to evaluate your their quality and robustness.
Use stress to precipitate and detect issues in NDF (No Defect Found) Boards