HALT, ESS and HASS: Methods That Work
(HALT 511)
Overview - why accelerated step stress?
Strength of materials in electronic hardware
Fatigue life and technological obsolescence of electronics today
Test to limits, determine root causes, learn the physics of failure, remove/improve weak
Stress testing for reliability
- 1970 -1980 Burn-in, Willis J. Willoughby's NAVMAT P-9492
- 1980's- today, AST and ESS - how and why current best commercial practices surpass military reliability
Why use stress in design evaluation and improvement?
- Benefits; limitations
- Types of stress stimuli
- Levels of stress
- Failure mechanisms and environmental stress
- Components and stress stimuli
- Systems and stress stimuli
Acceleration of electronic lifetimes
- Wear out modes in electronics
- Environmental Stress Screening stimuli - equipment and fixtures
- Thermal
- Vibration
- Combined chambers and combinations of stresses
- Methods of measurement
How to perform a step stress accelerated life test on electronic hardware
- Step Stress test at what assembly level?
- Determining when to use AST in the design process.
- Flowchart for highly accelerated life testing (HALT)
- When to use a single stimulus and when to combine stimuli
- Are failures under high levels of stress relevant to field reliability?
What equipment is needed?
- What data should we gather?
- How should we analyze it?
Test Plans - Development and determination of appropriate stimuli levels
- Highly accelerated stress screens (HASS)
- Proof of screen - How test can insure we don't damage good products
Examples of electronic systems HASS processes
- Concerns and long-term improvements in accelerated stress testing
- When do we stop screening?
- How do we optimize our screen?
- Optimizing the vibration and thermal fixturing
