Microcircuit Accelerated Testing Reveals Life Limiting Failure Modes

Accelerated life test investigations demonstrated that electrically biased life tests at ambient temperatures above 200°C provide a means for rapid identification of life limiting failure modes and associated use-temperature failure rates. Multiple manufacturers and lots of TTL, Linear and CMOS microcircuits were included in the investigations. Approximately 2900 microcircuits were subjected to extended life testing at ambient temperatures between 125°C and 285°C at electrical bias conditions between 0 Vdc and the manufacturers\´ rated voltage. Analysis of over 1300 life test failures showed that the predominate failure mode at both the 125°C test temperature and the accelerated test temperatures was parameter value shifts to out-of-tolerance conditions as a result of surface related failure mechanisms. Specific forms of surface instability, such as ion drift in or on SiO2 insulators, and surface state/trapping mechanisms, were identified in less than 4,000 hours of test at temperatures above 200°C, whereas, only the most severe cases of surface instability were identified in 4,000 hours of testing at 125°C. In addition, complete microcircuit life characterization as a function of surface related failures was accomplished using the data from the accelerated life tests. Bimodal failure distributions comprised of two lognormnal failure distributions ("Freak" and "Main") were observed in most cases. A short high temperature burn-in to eliminate the "Freak" population of microcircuits usually resulted in several orders of magnitude improvement in use-temperature failure rates. An Arrhenius reaction rate model provided a good representation of the relationship between microcircuit median lifetimes and junction temperature, and activation energies between 0.