Reliability assessment of electronic components exposed to long-term non-operating conditions

The decreased availability of MIL-SPEC components is forcing designers of low volume complex electronic systems, such as avionics and defense electronics, to consider the use of commercial off-the-shelf plastic encapsulated microcircuits (COTS PEM's), Traditionally, designers of these long-life, high reliability systems have been reluctant to use COTS PEM's because of concerns related to their capability to survive in harsh environments over long periods of continuous or intermittent operation. Many commercial insertion studies in the last several years have now conclusively demonstrated that PEM's made using best commercial materials, processes, and quality techniques will permit devices to perform reliably in the most severe environments. However, only recently have studies focused on the reliability of PEM's in that subset of applications requiring short time operation after long periods of unpowered storage (10 to 20 yrs). This paper presents the results of five critical commercial insertion studies focusing on long term storage reliability. These studies include analysis of PEM's, hermetic microcircuits, and assemblies stored for up to 28 yrs in various storage locations around the world. Regardless of the storage conditions, commercial grade PEM's, without screening or incoming inspection, survived assembly and extended storage, even though, in some cases, degradation was observed on the boards.