COTS Journal Article Reliability Implications Derating High-Complexity Circuits

initiatives, OEMs of military systems were authorized to use performance-based specifications for component procurement. At first, the industry was suddenly faced with a dilemma—to continue designing with tried and proven military-grade components or accept the risk of using COTS components in a manner historically considered unacceptable. But since then, there have been volumes of papers authored and presented on the topic of using COTS microcircuits in traditional military environments. But the trouble is, not all COTS ICs work in all military applications. Besides the issues of plastic package hermeticity and long-term storage, making nonmilitary devices work in wider-than-datasheet environments has spawned a movement of derating components in order to upscreen them. And with today’s state-ofthe-art submicron technologies and package configurations, the derating of high-complexity, leading-edge components such as microprocessors and DSPs has become very complex, and there’s much more involved in the process than meets the eye (Figure 1). In a number of applications, such as military ground-based communication systems, the environment might be the same as seen in commercial applications. In these cases COTS plastic-encapsulated microcircuits (PEMS) might be an acceptable choice. They might be used as is with good results—providing that obsolescence issues are addressed. But in other applications, such as missile systems, the use of COTS components often requires the OEM to operate the components outside the component manufacturer’s data sheet specifications. Historically, military OEMs have had established methods of estimating component reliability under various operating conditions. And even though efforts are now underway by multiple OEMs and third-party research organizations to develop “cookbook” methodologies to uprate or upscreen COTS components, the design margins for state-of-the-art devices that military OEMs once understood and came to rely on are no longer always valid. Even worse, reliability may suffer if the proper derating assumptions aren’t applied. Education, knowledge, testing and questioning assumptions are critical steps to consider when derating components.