What is Environmental Stress Testing?

All the products and materials around us are continuously exposed to various environmental stressors. 

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For this reason, environmental stress testing is used far and wide across various industries to evaluate how materials react to conditions such as humidity, extreme temperatures, sudden changes in temperature or humidity, and much more.

In the following article, we will delve deeper into Environmental Stress Testing, including the types there are, the sectors involved, and the tools used to conduct it.

How the Environmental Stress Test is Conducted

Environmental stress testing can be conducted in two main ways, known as HALT (Highly Accelerated Life Test) and HASS (Highly Accelerated Stress Screen). Both focus on how products react to extreme environmental conditions, but they do so with different objectives and methods.

• HALT (Highly Accelerated Life Test): The goal of a HALT is to identify the endurance limits of products by exposing them to extreme temperatures and humidity conditions to pinpoint failure points. During these tests, materials are subjected to rapid and intense temperature changes (such as cycling between extreme heat and freezing cold) and high humidity levels. The conditions are extended well beyond the product's normal operating parameters to identify critical points and improve the design. HALT testing is especially useful during the development phaseto obtain information on the product's endurance margins and potential failure points.

• HASS (Highly Accelerated Stress Screen) Test: Unlike HALT, HASS testing is used on products ready for production, and its goal is to detect any manufacturing defects or compromised materials. Here too, climatic cycles with extreme temperatures and humidity, but with more moderate parameters than HALT, so as not to damage the products but to ensure they function correctly within the specified operating limits. HASS testing allows you to uncover hidden defects that could emerge under real-world conditions and helps ensure that only reliable products reach the market.

These tests are performed inside environmental chambers.

Environmental chambers are laboratory instruments designed to precisely replicate and control climatic conditions, such as temperature and humidity. These chambers allow product reactions to be monitored in real time, ensuring the timely identification of any critical issues or defects.

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Which Industries Are Involved in Environmental Stress Testing?

Given the universality of environmental stress, many sectors are involved in environmental stress testing. Among these, however, we can list the main ones:

• Aerospace and Defense: These industries must ensure that electronic and structural components can operate in extreme environments. Procedures are outlined in MIL-STD-810.
• Automotive: Automakers use environmental testing to ensure that vehicle components remain performing well under changes in temperature, humidity, and vibration, in accordance with standards such as ISO 16750.
• Electronics: Both consumer electronics and components undergo a rigorous series of tests to ensure optimized performance in all environmental conditions. In this field, IEC 60068 is one of the primary references for environmental robustness testing.

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The FDM Environmental Chamber for Environmental Stress Testing

FDM environmental chambers are an ideal solution for those who want to conduct reliable and precise environmental stress tests. 

Thanks to the controller stillFACE and the revoFACE, our environmental chambers can conduct all the tests listed above, assisting the operator in all phases of the procedure.

FDM – Environment Makers has been a leader in the environmental testing industry for over 70 years. Our technicians are also available to work with customers to design instruments suited to their needs.

For any further questions or concerns, please do not hesitate to contact us.

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Reference Standards

• MIL-STD-810H — Environmental Engineering Considerations and Laboratory Tests
• MIL-STD-883 — Test Method Standard for Microelectronics
• IEC 60068 (series) — Environmental testing electronic components
• RTCA DO-160G — Environmental Conditions and Test Procedures for Airborne Equipment
• IEC 60721 (series) — Classification of environmental conditions (reference classification of environments)
• ISO 4892 / ASTM G154 — Artificial weathering of plastic materials

Authoritative Sources

• IEC 60068 — Environmental testing standard suite.
• MIL-STD-810H — Defense environmental testing standard.
• IEST — Institute of Environmental Sciences and Technology — Environmental testing best practices.

Frequently Asked Questions about Environmental Stress Testing

What is the difference between ESS, HALT and HASS?

ESS (Environmental Stress Screening): Non-destructive testing on 100% of production to eliminate latent defects (burn-in + thermal cycling + random vibration). HALT (Highly Accelerated Life Test): Destructive testing in R&D to find extreme operating margins (step stress up to breakdown). HASS (Highly Accelerated Stress Screening): A version of HALT for production, with reduced levels (50-80% HALT) and non-destructive testing. Focus: HALT = design robustness; HASS = quality screening; ESS = burn-in standard.

What stresses are combined in a complete environmental test?

The most common stresses: temperature (hot/cold cycling), humidity (damp heat), vibration (random/sine sweep), mechanical shock, pressure/altitude, UV/solar radiation, salt spray (ISO 9227), dust/sand (IP6X), water (IPX0-9), EMC (electromagnetic interference). MIL-STD-810H and DO-160G define 28+ method categories. For critical applications, multiple stresses are combined simultaneously (e.g., vibration + temperature + humidity in a combination chamber).

How long does a typical ESS test take?

Variable: Rapid screening (electronic components) 4-8 hours with 6-10 thermal cycles from -40°C to +85°C and random vibration. Automotive ESS 48-96 hours with cyclic cycles + humidity. DO-160 avionics qualification: 500-2500 hours cumulative depending on category. HAST accelerated stress: 96-192 hours at 130°C/85%RH equivalent to 1000 hours of normal damp heat. The choice depends on the Mean Time Between Failures target and the cost/effect criterion.

How do you interpret failure data from a stress test?

They are analyzed with Weibull distribution (shape parameter β) to characterize failure mode: β MTBF (Mean Time Between Failures) is extrapolated using Arrh(thermal activation) and Norris-Landzberg (thermal cycling). An effective HALT test typically finds 5-15 distinct failure modes, each of which must be corrected in a design review. The results are incorporated into DFMEA (Design FMEA) and derating rules.