Environmental Stress Screening (ESS) Tests
Introduction
Environmental stress screening (ESS) is a process of exposing an electronic product or component to accelerated physical or electric stress in order to force latent defects to manifest themselves. The levels of applied stress are much greater than the stresses that the product is likely to encounter during normal operation to precipitate failures and reduce test time.
ESS provides the necessary checks to eliminate infant-mortality failures and ensure trouble-free operation under harsh operating conditions.
Types of ESS Tests and Test Conditions
Let’s take a closer look at some of the common ESS tests. Notice: the statistics for each test are for illustration only and may need to be adjusted as needed to meet to specific application and budget.
1. Temperature cycling
Test conditions: Alternating cycles of hot and cold temperature at pre-defined dwell time and at the rate of temperature change (e.g. 5 to 10°C per minute)
Detected defects: Wire insulation; defective harness termination; component parameter shift.
2. Thermal shock:
This test subjects a product to temperature extremes in a rapid, back-and-forth manner.
Test conditions: - 140 to +125°C for 20 cycles.
Detected defects: Defective components; defective solder joints, improper crimping.
3. Humidity Test
Test Condition: Subject unit under test to 90 to 95% relative humidity at 40°C for 96 hours.
Detected defects: Corrosion of metallization; absorption of moisture; electrolytic corrosion of joints of dissimilar metals.
4. Electrical tests
Test condition: Application of voltage in increasing steps from normal to 25 or 50% above normal while holding temperature above ambient mortality cases.
Detected defects: Bias levels higher than those expected during use.
5. Vibration test
Test Condition: Vibrate unit under test from 20 Hz to 2 kHz or at the frequencies of expected operation.
Detected defects: Loose contact; weak circuit breakers; solder joints, bonding defects, mechanical faults in the device.
Benefits of ESS Program
There are numerous benefits that can be gained from conducting ESS tests. Here we list a few:
Quality and Reliability Benefits
• Improves overall design quality of the process and the product
• Discovers and allows correction of weaknesses in design phase
• Reduces design cycle time and speeds corrective action for design and process problems
• Increases robustness of design
• Validates consistency and reliability of manufacturing processes
• Helps detection of latent defects in design and in marginally acceptable components.
Economic and Marketing Benefits
• Decreases overall development costs
• Reduces costly field trouble-shooting
• Helps in making commercial decisions, such as a product’s warranty period;
• Improves customer satisfaction
• Assures compliance with customer requirements
Conclusion
ESS is a useful process that exposes product weaknesses and allows you to make corrections in the design. It is a powerful tool in electronic designs. It can lead to a robust product design.
Its usefulness can be applied at various product development stages from prototype to pilot production to mass production.