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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: Robert Webb (rob.webb@uecd.co.uk )
Organization:Ultra Electronics, Controls Division, UK
Date posted: Mon Apr 29 8:57:40 US/Eastern 2002
Subject: Up-rating
Message:
I am seeking advice on up-rating to extend the operating temperature range of an equipment beyond that specified for individual components used. Is it an acceptable method to up-rate by functionally testing the equipment at the extended range, and not to individually test components at the extended range? Can you also please advise of any other sources of guidance on this subject. Regards Robert Webb


Reply:

Subject: Up-screening
Reply Posted by: B.W.DUDLEY (bdudley )
Organization: RAC
Date Posted: Tue Apr 30 14:06:42 US/Eastern 2002
Message:
Changing the parameters for equipment after it has been designed and built is very difficult to accomplish and has risk. The problem lies in the basic facts of the limits of the components to operate successfully at the increased stress levels. Some components have little problem in maintaining proper performance, while others such as microcircuits have significant problems. Functional testing is not the answer, this test is not sufficient to determine the long term effects of higher stress levels and does not screen out the weak components. The best process is to perform an analysis on the entire unit to determine which are the critical components. Then, you should apply high stress testing on a sample of these devices to determine the short and long term effects. Finally, individual 100% testing of the critical components should be performed to down select the population to a group that meets all the stress factors. These parts are then used in the assembly of the unit. A source of guidance for this process is the International Electro-technical Commission (IEC) Avionics Working Group directive “Use of Semiconductors Outside Manufacturer’s Limits” CA-AWG/2DC 200-XX.


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