When compared to the electronic systems in industries like commercial and industrial equipment, today’s avionics systems face several unique challenges. In addition to operating in rugged environments for long periods of time, they must also satisfy rigorous safety and reliability standards. Most importantly, unlike other industries, they must meet these standards while using commercial-off-the-shelf (COTS) semiconductor devices (logic, memory, etc.) and electronic assemblies that have been designed and qualified for other applications with less rigorous requirements.
These challenges are illustrated by the systems engineering “V” diagram below, which is typically used to show the flowdown of requirements along the left arm, and the up flow of products that satisfy the requirements along the right arm. In aerospace, the requirements start with the airframe manufacturers, and move down the supply chain to avionics OEMs (which may include several levels). From there, they go to assembly and sub-assembly manufacturers, and finally to parts and materials manufacturers. The finished products then flow up the supply chain in the same fashion. Unfortunately for aerospace, however, a “flow down limit” exists at the lower levels of the diagram, below which the aerospace industry has limited or no control over how the needed products are designed, produced, or qualified—or how their configurations are controlled throughout the production lifetime. These non-specialized products below the flowdown limit are where COTS parts originate.
This is where the most significant challenge for avionics systems manufacturers occurs: using COTS components in qualification. COTS component manufacturers qualify their parts using industry standard test methods (high-temperature operating life, burn-in, etc.) that are rarely adequate for aerospace. For example, modern semiconductor devices are targeted for markets that require service lifetimes of less than ten years, while avionics systems must reliably operate for decades. To address this problem, the aerospace industry has conducted research resulting in a wearout standard, SAE ARP6338. This standard describes a method to use credible data and analyses to address the wearout issue in avionics systems design, production, and in-service support, while also assuring customers of the long-term reliability of their systems. Likewise, the aerospace industry has also addressed the more general problem of application-specific qualification of COTS items through SAE ARP6379, which addresses challenges beyond semiconductor wearout.
Reliability Testing Standards and Methods in Aerospace System Design
While SAE ARP6338, SAE ARP6379, and other aerospace reliability standards have helped improve the quality of avionics systems, the tests are traditionally based on the extensive use of limited, credible data to perform realistic analyses in order to arrive at trustworthy conclusions. Unfortunately, this means the time and costs required to design and conduct these tests have become unacceptably high. Now, the challenge has become developing methods and tools that are capable of leveraging limited test data to assure the reliability of avionics systems in a range of applications, and Physics of Failure (PoF) methods have long had the capability to do just that. Their success has traditionally been limited, however, by their requirements for significant computing power, the difficulty in using them, and the need to validate their accuracy in critical applications such as aerospace.
However, increased computing power and advancements in computing technology have enabled organizations such as DfR Solutions to develop and validate advanced PoF software tools, and to validate their accuracy in a variety of applications, including aerospace.
In fact, we developed the latest version of our Sherlock Automated Design Analysis™ software in part to help “automate” PoF analyses and satisfy the requirements of SAE ARP6338, SAE ARP6379, and other standards for the use of COTS parts and assemblies in aerospace applications. Our new Semiconductor Wearout module can be used to predict the lifetime of high-technology semiconductor devices with respect to electromigration, time-dependent dielectric breakdown, hot carrier injection, and negative bias temperature instability.
To learn more about how you can evaluate the reliability and performance of semiconductor devices in high performance applications, read my previous blog post. You can also watch our free webinar to learn more about reliable implementation of COTS parts and assemblies into aerospace systems. Just click the button below.