The goal of ESS and HALT HASS testing is to deliver the most reliable product possible to the customer. However, each method achieves the goal differently, depending on application-specific timescales and costs.
For some applications, particularly where the operational limits are already extreme, a different approach is taken. Here Environmental Stress Screening (ESS) is applied, in which the key difference is that the stresses applied are within the normal operating parameters of the product being tested. As a global leader in high-mix low-volume manufacturing, we are dedicated to staying on top of the competitive landscape that manufacturers are faced with today, and constantly seek ways to deliver the most trustworthy products.
With the growth of the electronics industry, ESS has become an indispensable tool to allow manufacturers to produce failure-free products. This article covers ESS testing, its objectives, benefits, how it works, and why manufacturers should consider it.
What is Accelerated ESS Testing /Burn-in?
The goal of Environmental Stress Screening (ESS) is to precipitate product failure during the manufacturing time rather than after a product is shipped. ESS testing is the most cost-effective stage of the manufacturing phase. It's a part of the product development process that reveals hidden defects by applying stresses such as increased temperatures, vibrations and more to a product.
According to Wikipedia, ESS (environmental stress screening) "refers to the process of exposing a newly manufactured or repaired product or component (typically electronic) to stresses such as thermal cycling and vibration to force latent defects to manifest themselves by permanent or catastrophic failure during the screening process. The surviving population, upon completion of screening, can be assumed to have higher reliability than a similar unscreened population."
ESS is also known as Burn-in, AST (Accelerated Stress Testing) and allows manufacturers to eliminate the infant mortality of a product. Undetected defects will manifest as early life failures during field use.
Burn-in tests eliminate defective parts early to ensure product reliability. Generally speaking, it is better to "burn-in" at the component level when the cost of testing and replacing parts is lower.
History of ESS
Environmental stress screening (ESS) was first addressed in the annual meeting of the Institute of Environmental Sciences and Technology (IEST) in 1978 as a result of the growing demand for a standardized method to eliminate infant mortalities of electronic systems by the industry. [source]
It was initiated earlier in the space programs during the 1960s because of the extreme need for reliability. ESS has continued to gain recognition in the defence industry as a cost-effective quality control method.
How is ESS different from HASS?
ESS uses the product specification limits to test for product failure. HASS applies stresses beyond the product specifications but under the operational limits.
The difference between product specification and operational specification limits is that product specification limits stop at the maximum stress test for which the product is intended. Operational limits in HASS are over the top, knowing the product is set for failure.
Accendo Reliability wrote an informative article on ESS and HASS and included the various terms related to stress testing. A few worth mentioning are:
Specification Stress - Stress level limits expected during field use.
Operational Limit - Stress level at which the product does not perform correctly. The product typically recovers when the stress is removed.
Destruct Limit - Stress level at which the product is disabled. The product does not recover when the stress is removed.
Failure rates are often used as an index for reliability.
source: Bahret, Adam "ESS and HASS", Accendo Reliability https://accendoreliability.com/ess-hass/
Component Failure Rate Over Time
Three Stages of Failure - the "Bathtub Curve"
The graph below is broken down into three categories: decreasing, constant, and increasing failure rate. The constant failure rate can be viewed as the "useful life period."
Image source: [Bathtub curve], In Wikimedia Commons
Early Failure Stage/ Infant Mortality - failures occur at a high rate. An example could be material defects.
Constant (Random) Failure Stage/ Normal Useful Life - Because failures can occur sporadically, failure rates never decrease to zero.
Wear out Failure Stage / End of Life - are usually caused by age-related wear and fatigue.
Burn-in testing is a process to weed out failures from the first stage of the "bathtub" curve for reliability. It analyzes for effective reliability, meaning it can help predict the performance and lifecycle of a product.
Why Perform ESS in Product Development?
Manufacturers must consider the failure mode types caused by high temperature, thermal change, vibration, and more. Screening and thereby capturing any latent defects will greatly reduce infant mortality.
Furthermore, manufacturers must consider the challenges of designing ESS testing. Take for example, a product like an aeronautic component that is faced with drastic shifts in temperature. A product failure could be disastrous.
Stages in Product Development
source: ESS and HASS
Objective: accelerate early failures to fix and repair at the most cost-effective stage in product development.
Top Reasons / Benefits for ESS Testing
1. More robust product going to market
2. Testing is required if hoping to win a contract with the Department of Defence, e.g. conform to MIL-STD-810
3. Prove due diligence
4. Position a company ahead of its competitors
5. Build the most reliable product
6. Reduce warranty claims
7. Secure brand loyalty and customer satisfaction
8. Speed design cycle time
9. Reduce costs and improve profits
TT Electronics provides OEMs with an integrated, end-to-end solution throughout the product development cycle. This includes test recommendations before the manufacturing release. ESS is an essential testing method that allows manufacturers to dramatically reduce failure rates for products with extreme operation limits and is therefore a critical capability in an electronics manufacturing service provider.
TT Electronics' Testing Solutions (Abtest) facility is a UKAS accredited testing laboratory No. 0042. With more than 45 years of experience, we have the expertise to conduct a broad range of standard tests, as well as some of the most difficult testing procedures like Environmental Stress Screening (ESS). Our experienced technicians can develop robust test strategies and implement customer-specific test regimes onsite to help you deliver the most reliable end product.