Infant Mortality, Freaks, and Wear-Out: Application of Modern Semiconductor Reliability Methods to Ceramic Multilayer Capacitors

An overview of the methods of modern semiconductor reliability and accelerated life testing based on the lognormal distribution is given, Bimodal distributions due to the presence of freak failure populations are also discussed, along with the Fowlkes test for a bimodal lognormal distribution. A novel analysis of recent published results on capacitor reliability is given, based on the known properties of the lognormal and Weibull distributions as well as recent experience in their application to semiconductor device reliability. For test periods of 168 and 1000 h, estimates of the required voltages and temperature stresses as well as sample sizes are made to ensure a hazard rate of less than 100 FIT (failures per unit time) per capacitor after 40 yr of operation. The results show that the customary accelerated test at twice the rated voltage and 125°C for 1000 h, is insufficient. Comparison with data from a recent highly accelerated life test (HALT) indicates that the HALT procedures may be useful as an effective screen. Bimodal failure distributions are shown to be due to the presence of freak (early failure) populations of about 10%.