Published in Mil Tech Insider
How rugged is “rugged”? The answer to that question should have a clear and consistent answer that gives system integrators the confidence and surety that a specific module from a commercial off-the-shelf (COTS) supplier will perform and survive in the conditions their application requires. All too often though, claims made by COTS vendors that their module will meet a certain range of durability (temperature, shock, and vibration) are not based on a common, industry standard that enables the customer to make meaningful comparisons between different boards from different vendors.
In general, it can take multiple years from when a system integrator starts developing a specific set of modules to when the system actually goes through qualification and then enters deployment. Because of this extended time frame, a latent thermal or mechanical design issue could remain undiscovered for a very long time. The later a problem is uncovered, the more expensive it is to fix. While it may be impossible to test for every possible scenario, the more robust the up-front module qualification is, the more information can be provided to the system integrator. Provided with that data, the likelihood of a system integrator encountering a module-level reliability issue is greatly diminished.
Additionally, few COTS suppliers have the means to define long-term reliability when faced with the repeated temperature cycling conditions of deployed platforms. Today’s airborne systems, for example, experience a regular and recurring pattern of temperature extremes that microscopically stresses electronic assemblies in ways that can cause failures over time. Complicating matters is the simple fact that there is wide variation among COTS suppliers as to what qualification is actually performed on their rugged modules.
The good news is that such a durability standard already exists: The VITA Standards Organization’s ANSI/VITA 47 targets the Environments, Design and Construction, Safety, and Quality for Plug-In Units. Even better, the standard is currently being updated to address the ruggedization requirements of emerging new COTS applications, such as space and unmanned underwater vehicles (UUVs). VITA 47 includes the environments specified with different levels for different ruggedness grades: operating temperature, nonoperating temperature, temperature cycling, vibration, and operating shock. For the popular conduction-cooled module format, the levels for these environments vary in severity from ECC1 to ECC4 (as shown in Table 1). One of the purposes of VITA 47 is to provide more commonality to the ruggedization and qualification process by detailing pass/fail criteria for different environmental conditions. This makes it possible to standardize the specific environmental conditions that a module is being subjected to when it undergoes qualification.
One notable aspect of VITA 47 is that it defines a method for determining long-term reliability due to thermal cycling. VITA 47 defines a series of 500 thermal cycles. For ECC4 level testing these cycles range from -55 °C to +105 °C, and the associated test subjects modules to more than seven weeks of continuous thermal stress. Following VITA 47 guidance, integrators can correlate the thermal testing data to their platform long-term reliability targets, which, depending on the target platform, can equate to five, 10, or 15 years of active service life.
It’s time for VITA 47 to be embraced throughout the embedded market. Doing so will help eliminate market uncertainty through the use of a common standard to define environmental testing, safety, and quality requirements. As Jerry Gipper, VITA’s Executive Director, puts it, VITA 47 makes it “easier and faster for users to determine if a specific product will meet their environmental requirements. This enables users to verify that a specific plug-in module is applicable to a target application and will result in the desired system reliability.”
Curtiss-Wright has integrated the VITA 47 Standard – including ECC4 – into its standard reliability-testing practices. Full test reports are available for select products.
For system integrators, when asking how rugged a module is, the answer shouldn’t be “That depends on your definition of rugged.” VITA 47 gives the COTS industry the tools to provide customers with greater ruggedization plus knowledge and confidence about products’ reliability. It’s time to put those tools to work.
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