Manufacturers want to make sure their products are dependable and free of defects, especially in sectors that place a high value on reliability. One way to do this is to conduct environmental stress screening, or ESS. But what exactly is ESS, and how can you get started with it? This ESS testing guide will provide you with those answers and more.
What Is ESS Testing?
ESS testing is a part of the product development process that aims to reveal any hidden defects by applying accelerated environment stresses, such as vibrations or thermal cycling, to a product. ESS is an umbrella term that refers to various testing procedures that accomplish this. These tests may be relatively basic or more severe, depending on the circumstances. ESS testing helps to prepare products for their real-world applications, so the testing conditions will often be the most extreme which the product may face in the real world.
Conducting ESS tests on new products enables the manufacturer to correct any flaws that would otherwise have affected reliability. After performing tests and correcting defects, the products will be more reliable as compared to a new product that did not undergo screening. Successful ESS testing will eliminate “infant mortality” defects in products.
ESS began in the space programs during the 1960s because of the high need for reliability. The military has also played an integral role in the development of ESS testing, and every military department uses ESS a part of its major systems acquisitions. Still, the aerospace industry and the defense sector are the primary users of ESS testing. Though other sectors can apply it, it is less common in industries such as consumer electronics.
The Benefits of ESS Testing
Conducting ESS testing has numerous benefits including technical benefits, financial benefits and those related to reliability and quality control.
1. Technical Benefits
ESS helps to improve the design undergoing testing, giving it an advantage over its competition in the market. It enables the discovery of defects and their correction during the prototyping phases, rather than later, such as in the preproduction phase. This speeds design cycle time and correction action. ESS testing also helps ensure a design will pass design specification qualification tests and makes the design more durable overall.
2. Quality and Reliability Benefits
A primary benefit of ESS is the improvements to the quality and reliability of a tested product. ESS tests can reveal flaws in design or manufacturing, enabling them to be corrected. Testing can improve the design, validate the consistency of manufacturing processes and reveal the reasons for any reliability problems within the manufacturing process. Conducting tests before delivering a product to customers also raises mean time between failures.
3. Financial and Marketing Benefits
Conducting ESS testing can help to reduce costs and improve profits. ESS is regarded as a cost-effective quality control process and produces a high return on investment. It decreases costs during development and production by helping to catch defects earlier. Increased reliability also translates to reduced in-field troubleshooting.
It can also increase profits by speeding time-to-market and ensuring compliance with the requirements of customer contracts. Reduced overall costs can also produce a cost edge over bids from competitors. The enhanced reliability of a product will also improve customer satisfaction and the company’s reputation, leading to more sales in the future. Detecting faults before sending a product to market can also help avoid the costs of recalls, warranty payments and lawsuits, which can be expensive and damaging to a company’s reputation.
How Does ESS Testing Work?
There are various types of ESS tests. The one used in a given situation depends on the product, whether a single component or the whole unit is being tested, the environmental conditions the product will be exposed to and reliability requirements. ESS typically involves temperature, electrodynamic vibration testing or both.
To conduct the test, testers place the product in an environmental chamber and monitor it as vibrations, temperature changes and other stimuli are applied to find defects in the product being tested. Thermal testing may find faults related to seal and gasket failures, insufficient wiring insulation and other component-level defects. Vibratory testing is more likely to uncover loose hardware and connectors, insufficiently torqued screw assemblies and weaknesses in switches and circuit breakers. When using a combination of thermal and vibratory testing, you may uncover various other failures as well.
How ESS testing works depends on the level of assembly you are screening. You may need to conduct testing on the part level, assembly level or unit level. Different stress types work best for varying levels of assembly since the structural and thermal characteristics of the test subject changes, causing different responses and defects to appear. Testing on the part level first enables the detection of faults earlier in the development and production processes, reducing the costs of fixing the defect. Testing at all levels, though, helps to ensure the quality of the overall product.
On the component level, you may test for chip-related or die-related failures due to the fabrication processes and package-related faults caused by assembly errors and apply temperature cycling and thermal shock tests. For assembly-level screens, you may need to conduct thermal cycling or random vibration tests.
Types of Tests
At Quality Testing Services, we provide a variety of ESS testing services, including:
- Combined Temperature and Electrodynamic Vibration
- Rapid Transition Rates
- Profile Execution for Extended Test Durations
- “Shake and Bake”
- Thermal Vacuum (TVAC)
We conduct these tests in dedicated environmental test chambers with advanced testing equipment, and we have the flexibility to work with our clients to determine the best ESS testing processes for their needs.
How to Get Started With ESS Testing
So, how can you get started with ESS testing? Successfully performing ESS tests requires proper planning. The first step is ensuring that ESS testing is the right approach for your needs. Then, you can determine what kind of ESS test to perform.
1. Reasons to Conduct an ESS Test
One of the most common reasons for conducting ESS testing is the fact that it’s required by regulations or the standards of the organizations the manufacturer is doing business with. Many organizations require the manufacturers they work with to conduct ESS testing as a part of conforming to their standards. Other times, a product must meet requirements that include ESS testing before it can be used in a certain industry. Components used in the aeronautics sector, for example, must conform to FAA standards.
Even if regulations or standards don’t require ESS testing, your company may wish to pursue it. It can help to increase the reliability of a product, reduce costs and increase profits. It can also help companies avoid costly mishaps that may result in recalls or lawsuits. ESS testing may be especially useful to a company if their product will be exposed to harsh conditions such as rapid temperature changes or persistent vibration.
2. When to Do ESS
You also need to decide when to conduct ESS tests. It can be beneficial to perform them at many different points throughout the process of taking a product from an idea to the market. It can be valuable to conduct ESS testing during product development, prototyping, pilot production and production.
Planning should begin early to ensure a successful testing process and because testing conducted early in the process has more cost-saving potential. By the time production begins, you should have plans for ESS testing in place that include the resources you will use, any training requirements, the levels of the assembly to be tested and the relevant screening profiles. For testing failures that are not design-related, it’s best to have plans ready by the engineering and manufacturing development phase.
4. Choosing an ESS Profile
Choosing as ESS profile is an important part of getting started with ESS testing. Guidelines, such as those published in military documents and by organizations like the Institute of Environmental Sciences and Technology, can help you to establish your ESS profile. These guidelines provide you with starting points for determining ESS stress levels. You can then refine the levels in these guidelines using screening strength models that evaluate the impact of various stress levels, screening durations and testing approaches.
Conducting a Highly Accelerated Life Test, or HALT, is another approach that can help you determine an ESS profile. HALT can allow you to establish operating and destruct margins, uncover weaknesses early in the product’s lifecycle and determine the effective stress limits for Highly Accelerated Stress Screening, or HASS. HALT involves incrementally increasing stress levels until normal parameters of use are surpassed and failure occurs. This test helps to uncover the weakest parts of a product. It is typically conducted on a few units to determine appropriate levels for HASS, which is then performed on all units.
If conducting screening at the component level, having knowledge of the failure modes for the components being tested can help you to choose the appropriate screens. Understanding the accelerating stresses that cause these failure modes can be valuable as well.
Considerations for ESS Testing
There are many different factors that go into conducting successful ESS testing. It requires ensuring precise testing conditions and execution. Besides the ones listed above, there are some other ESS testing considerations that can impact the success of your testing.
1. Power On or Power Off
When testing electronic components and products, you must determine whether it is best to screen with the power on or off. This question would arise during the planning process. The assembly level you are testing plays a role in answering this question.
When testing entire units, it should be powered during the screening to replicate real-world use as well as possible. Components being tested are often powered on as well, but assembly-level tests are less likely to be powered. This is because the fixtures for mounting and testing individual components are typically simpler and less expensive than those for assemblies. There is more variation among assemblies, so generic assembly test equipment is not common.
2. Pre- and Post-Screen Functional Testing
Another vital component of ESS testing is functional testing, which should be conducted before and after each screen. This test simply involves checking the functioning of the item being tested and enables you to determine the failures that the screen caused.
Pre-screen functional testing is important because it enables you to identify any defects that were present before the screen. Without a pre-screen functional test, it would be impossible to tell which defects were caused by the screen and which were pre-existing. This could lead you to evaluate a screen as effective when it, in fact, was not. Post-screen functional testing allows you to detect the defects that occurred during the test. If the item was not powered on and monitored during the screen, this could be especially important since it may be harder to detect defects under these testing conditions.
It’s important that functional tests are performed immediately before and after a test so that you can be sure that any defects occurred during the screen and not during cleaning, handling or at any other point. Ideally, the pre-screen and post-screen functional tests should be conducted while the test item is still in the chamber. The functional tests used before and after a screen should also be identical so it is clear the stress applied caused the fault.
It is also important to conduct functional testing before and after applying each stress rather than just before and after the full screening process. This will enable you to determine the effectiveness of each stress, and you can use this information to adjust your screening process. It can also be useful to conduct functional testing while applying stresses if possible. This helps in identifying intermittent faults and those sensitive to temperature and timing.
3. Types of Equipment Available
The equipment you need and have available is another important factor. The types of equipment you require can significantly impact the cost of the testing process and its complexity. Generic testing fixtures are more widely available for components. For assemblies and units, you may need to devise custom fixtures. Some common types of ESS testing equipment include:
- Single-axis electromagnetic shakers
- Single-axis hydraulic shakers
- Pneumatic hammer excited tables
- Electromagnetic shakers with skewed table
4. Environmental Testing Labs vs. In-House Testing
Another important consideration is whether to conduct testing in a professional environmental testing lab or in-house. Conducting testing in-house requires investing in your own testing equipment and training. When working with an environmental testing lab, you benefit from lower upfront costs and the experience of trained professionals.
Get Your ESS Testing From Quality Testing Services
At Quality Testing Services, we provide ESS testing and a range of other testing services with an emphasis on fair pricing, flexibility and meeting our customers’ needs. We work with our clients to help them create the best products possible. Testing, such as environmental stress screening, is an essential part of that for many types of products. You can learn more about what we offer by contacting us online or calling our California office at (714) 903-1155, or requesting a quote.