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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Rushabh
Date posted: Mon Mar 5 15:13:43 US/Eastern 2007
Subject: Why failure rate of a capacitor is higher for non-operating vs operating condition
Message:
Can you please try to find the failure rate with 10% duty cycle ? I might be that for 0% duty cycle calculation there is some bug in software. Ideally what you pointed out is correct. Operating mode failure rate should be higher than Non Operating.


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Reply:

Subject: Capacitor failure rate for specialized scenario
Reply Posted by: David Dylis (ddylis@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Mar 5 16:49:27 US/Eastern 2007
Message:
For the specialized situation that you identified, PRISM does calculate a higher failure rate for multi-layer chip capacitors in a Non-Operating environment then in the Operating scenario.

The parameters you have chosen for environment and usage have negated the affects of temperature cycling, vibration, power on/off cycling, and component stress from the analysis for the capacitors in question. Therefore, the operational, cycling and solder joint portions of the capacitor failure rate are zero for the capacitor in your operational and non-operational scenarios (please review the PRISM failure rate tab for each component). The only factors that remain are the non-operational and EOS/ESD failure rate contributions. For capacitors, the EOS/ESD failure rate is a constant that does not change based on operation/environment. The failure rate due to non-operation is zero for a capacitor that is operating at a 100% duty cycle while there is a non-operational failure rate for a capacitor that is in a non-operating scenario. As a result we now have a capacitor with a predicted non-op failure rate that is higher than what is predicted in the operational scenario.

You have identified a specific set of parameters that negate the operational portion of the capacitor failure rate. This issue needs further analysis and will require update to the capacitor model in a future PRISM version. In the meantime, I recommend that you use the PRISM default parameters for stress and capacitance when performing an analysis based on your operational conditions.

If you have any additional questions, feel free to contact me.


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