Polymer technology is changing dramatically the capacitance landscape in what concerns electronic design. Still not evident to every engineer, the passive component, as we know, is usually one of the last concerns. But, spending some time about “what’s different”, engineers are understanding that this new technology offers new possibilities of Ripple Capability (2 to 3 times Higher than Standard Tantalums), higher capacitance in a frequency range above 100kHz and opens the possibility for new derating rules.
These arguments may represent a lower cost of ownership and enable an effective downsizing of the case sizes used and board space. Until today, when a customer was looking for an ultra-low ESR solution with a certain grading level, wouldn’t see polymer capacitors as a possible choice.
These capacitors were not suitable to apply the existing MIL-PRF-55365 Weibull Failure Rate Estimates. The model would require extended testing hours in order to get the first parts failing, so, not applicable.
KEMET developed one method that makes possible to grade the capacitors. The purpose of this post is to briefly describe the method employed to assess lot reliability for KEMET’s T540 and T541 Series. The objective of this method is to assess 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 essence of the method is to test a significant representative sample of each manufacturing lot ordered with this feature under accelerated voltage and/or temperature conditions to obtain the necessary unit hours with an Accept/Reject (A/R) Number of 1/2 to demonstrate the claimed reliability level.
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.
The procedure is as follows:
- Randomly select sample of predetermined size (at least 100 capacitors).
- Mount components with an additional reflow (two (2) total reflows) to test boards using conditions per IPC/J-STD-020D that are consistent with the capacitor terminal finish.
- Life test components using pre-determined conditions of time, temperature and voltage.
Count failures at the end of the test to demonstrate that the desired reliability level is achieved based on the A/R of 1/2.
This feature is an option already available in the T540 and T541 Series. To order with a B, C or D Level, please consider the ordering info in the product catalog.
 | Evaluation of Polymer Counter-Electrode Tantalum Capacitors for High Reliability Airborn Applications.pdf |
 | New High-Reliability Assessment Practices for Tantalum Polymer Capacitors.pdf |