Reliability Derating Procedures

The objectives of this study were the establishment of derating parameters and levels for electronic parts, development of thermal models, creation of temperature verification methods, and the development of the framework leading to the creation of a military standard for derating of parts. The results of this study revealed that derating data on complex devices are difficult to obtain so an alternate approach was used involving failure rate data from MIL-HDBK-217 and specific failure mode information. Thermal models, both internal and nodal, were developedafor six package types and temperature tests results for one of these types were compared to the theoretical value. The comparison was extremely favorable. The objective of the Reliability Derating Procedures program was to develop the framework leading to the creation of a military standard for the derating of electronic and electromechanical devices for Air Force application. Primary areas of investigation were: (1) relationship of case temperatures to junction temperatures, (2) methods of verifying that derating has been accomplished, (3) relationship of reliability to cost, (4) derating standards for complex devices, (5) creation and verification techniques through data collection and testing.