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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

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

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Posted by: Christophe Crocombette ( )
Organization:Electricite de France
Date posted: Tue Feb 9 7:42:22 US/Eastern 1999
Subject: Reliability of electronic parts and long time storage
My company is being storing some obsolete parts for maintenance activities. I am looking for any information about the subject of electronic parts and long time storage : - failure mecanisms, - state of art of long time storage conditions in the industry - etc. If you cope with the same problem, please let me know what your approach is... I have also some specific questions : Is dry nitrogen with regulated temperature (systematically) used for long time storage ? Are there specific recommandations about long time storage of electronic parts ? Is there a predictive method to calculate the reliability during long time storage ? Thank you ! Chris


Subject: Storage Reliability
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Mon Feb 15 13:47:37 US/Eastern 1999
The major failure mechanism that impacts most electronic and non-electronic items is corrosion. Other mechanisms include: electro-static discharge, contamination-induced, radiation and mechanical(temperature, vibration, shock, sand/dust). The first order of protection is to limit the exposure to any of the accelerating causes. Tight temperature and humidity controls are two excellent preventive measures. The introduction of nitrogen should reduce the exposure to chloride or sulfide ions, hence reduce galvanic corrosion. Calculation of long term storage is a difficult problem as the models and data base previously used are now over 15 years old as shown by, RADC TR-85-91 "Impact of Non-operating Products on Equipment Reliability". Other methods include: the use of zero stress factor failure rates translated to storage conditions or estimations from equipment level data. Both are limited to the data avialable and the ground rules used to evaluate the data. Of course, one could preform detailed physics of failure calculations for all failure mechansims and materials to determine the "exact" time of wear-out if you have the time and resources. The Reliability Analysis Center is preparing a new technique for forecasting reliability which contains storage estimating conditions for electronic parts. This product, called "PRISM", should be available some time in the spring of 1999.


Subject: Storage
Reply Posted by: Mark Mobley ( )Baker Hughes Inteq
Date Posted: Tue Mar 23 11:48:45 US/Eastern 1999
Nitrogen storage - Use dry nitrogen, plastic packages may absorb up to 6% or more of their weight in moisture. After a bake out, if possible vacum pack the components in a dry nitorgen atmosphere with desicant. Note moisture gets to the IC, the passivation glass in the IC may have phosphorous in it, hence you get phosphoric acid. This is valid especially for older parts before nitrides were commonly used.

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