DEMONSTRATED RELIABILITY OF PLASTIC-ENCAPSULATED MICROCIRCUITS FOR MISSILE APPLICATIONS

For the past decade, overall reliability improvement and product avail ability have enabled plastic encapsulated microcircuits (PEM) to move from consumer electronics beyond the relatively large and reliability- conscious (due to harsh usage environments) automotive market, into th e military market. Based on the analysis of the worst-case PEM scenari o for military applications, demonstrating the moisture reliability un der long-term (20 years) dormant storage environments has become the l ast hurdle for PEM. Recent studies have demonstrated that PEM can meet the typical missile environments in long-term storage. To further val idate PEM reliability in missile applications, Texas Instruments (TT) recently conducted three separate studies involved 6 years of PEM mois ture-life monitoring and assessment, testing of the standard PEM elect rical characteristics under the military temperature ranges (-55 degre es C to -125 degrees C), and assessing their robustness in moisture en vironments after the assembly processes. These TI studies support the use of PEM in missile (or similar) applications. However, ''not all pa rts (PEM as well as hermetic packaged devices) are created equal.'' Ef fective focus on part and supplier selection, supplier teaming, and pr ocess monitoring is necessary to maintain the PEM reliability over the required environments at the lowest cost. This paper assesses PEM rel iability for a selected missile storage environment using the industry -standard moisture testing, such as biased HAST or 85 degrees C/85%RH (relative humidity), for demonstrating the PEM moisture survivability, The moisture reliability (MTTF) or average moisture lifetime of PEM i s assessed to correlate PEM capability to anticipated field-performanc e environments.