This week (May 23, 2016) KEMET is exhibiting at the Aerospace Expo (2016) in Pasadena, California. Our product experts are on-hand to answer questions related to high-reliability and aerospace applications. In particular, we are eager to discuss KO-CAP’s new Established Reliability testing and here is why.
It is entirely possible to use commercial-off-the-shelf (COTS) components in high-reliability and military projects, provided that they have received the appropriate screening and qualification. Applicable reliability standards have been established for various component types such as MIL-PRF-55182 for metal-film resistors and MIL-PRF-55365 for electrolytic tantalum chip capacitors. These reliability standards define accelerated life test conditions and reliability targets for various levels, including Established Reliability (ER), non-ER and Space Level capacitors.
Failure rate data for components can be obtained by performing accelerated life tests under conditions specified in the MIL-PRF standard. Screening tantalum capacitors by MIL-PRF-55365 usually involves a combination of surge current testing and Weibull screening which includes burn-in to remove infant mortality failures followed by reliability quantification.
The acceleration factors developed for MIL-PRF-55365 apply to MnO2 type (often referred to as “classic tantalum” or “solid tantalum”) capacitors but are found to be unsuitable for polymer-type tantalum devices. (Read this article to learn the difference between MnO2 and Polymer capacitors.) Currently, there is no MIL-PRF document directly applicable to the polymer tantalum capacitors. Until recently, engineers wishing to use these devices in military projects have had to consider developing custom methods for screening devices.
KO-CAP’s Established Reliability Screening
However, KEMET has developed a method to assess lot reliability for its COTS high-reliability polymer electrolytic T540 and T541 Series. The objective of this process is to determine reliability levels corresponding to 0.1 Percent Per 1,000 Hours, 0.01 Percent Per 1,000 Hours and 0.001 Percent Per 1,000 Hours. The T540 and T541 Series is the first polymer electrolytic capacitor available with failure rate options defined by the KO-CAP® assessment method.
The fundamental principle is to test a significant representative sample of each manufacturing lot ordered with this feature under accelerated voltage and temperature conditions to obtain the necessary unit hours with an Accept/Reject (A/R) Number of 1/2 to demonstrate the claimed reliability level. As an example, to achieve a reliability level of 0.001 Percent Per 1,000 Hours, 1 failure is allowed in 108 accumulated part hours. For the lower reliability levels, fewer part hours are required. The acceleration factors are predetermined for each design based on testing conducted under multiple conditions of temperature and voltage. The assessed reliability is equivalent to steady state operation at +85°C and full rated voltage as are the MIL-PRF-55365 Weibull Failure Rate Estimates.
For more information, the Polymer Reliability Assessment Test whitepaper outlines the test in detail.