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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: RS Moore (bob.moore@bae.co.uk )
Date posted: Thu Sep 9 11:24:09 US/Eastern 1999
Subject: Life assessment for thermally shocked product
Message:
My company has recently undertaken thermal shocking of a small (0.6" x 0.6") hybrid-like device. This involved 450 thermal cycles from -50C to +90C in 60 seconds with 30 minute temperature dwells at each extreme. The product was unpowered. Am I able to determine an estimate for the product's life based on the testing described above and if so how do I go about it? Thanks, Bob


Reply:

Subject: Product Life Assesment
Reply Posted by: Dave White (white@spectralsolutions.com )
Organization: Spectral Solutions, Inc.
Date Posted: Wed Sep 15 12:08:48 US/Eastern 1999
Message:
Bob, I'm afraid that you will need more information before you can make an estimate of product life. What are the failure modes of the product? Did the testing you described help to accelerate any failures? Were the failures noted with respect to when they occured? Are there any other failure modes not effected by this test? What is the actual environment that the product will be exposed to? As a start I would recomend reading Wayne Nelsons book on Accelerated Testing. It has a lot of useful information. Good luck.


Reply:

Subject: Life Assessment
Reply Posted by: Bruce Dudley (bdudley@alionscience.com )
Organization: Reliability Analysis Center
Date Posted: Thu Sep 16 10:55:53 US/Eastern 1999
Message:
The thermal shock testing that you are appling to the hybrid like devices appears to be a product screen type test as apposed to an accelerated life test. To determine the life characteristics of a product, one should test the units (a large sample) so that a high percentage fail due to the stress characteristics. Using damage accumulation assessment techniques (Miner's Rule) you should be able to determine the expected life based on the accelerated test results. Suggest that you review MIL-HDBK-344A Environmental Stress Screening for information on temperature shock testing and the damage accumulation process.


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