HALT, ESS and HASS: Methods That Work

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