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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: Tom Donnelly ( )
Date posted: Sun Jan 3 1:59:31 US/Eastern 1999
Subject: Screening solder workmanship
I am currently working with space related hardware. The issues I am having are with solder joint reliability and possible sources for specific failure rate information as it relates to the thermal stress testing of PWB's. What is the difference in solder joint failure rates when the electronic equipment is exposed to -45F versus -30F? and what failure mechanism's did I miss by only exposing the equipment to -30F. I have the same question for taking the equipment to +60F instead of +85F. What is the differnce in failure rates for the solder connections and what failure mechanism's did I miss. From my many years in Reliability I believe that the difference is insignificant, but my customer's would like me to quantify it....I appreciate any thoughts you could contribute to solving this problem...... T.Donnelly

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Subject: Solder Screening
Reply Posted by: Bruce Dudley ( )
Organization: Reliability Analysis Center
Date Posted: Wed Jan 6 10:46:14 US/Eastern 1999
Expanded temperature differences, both high and low, can cause reduced reliability values especially when temperature cycling is applied. A fatigue failure equation to estimate the reliability of a surface mount solder joint is contained in the MIL-HDBK-217 " Reliability Prediction of Electronic Equipment". This equation accounts for delta temperature differences, cycling rates and circuit board substrate thermal coefficient of expansion changes. The greater the delta temperature or cycling rate, the lower the reliability expected. If screening is the process that you want to examine, then MIL-HDBK-344 "Environmental Stress Screening of Electronic Equipments" has techniques for thermal and vibration testing conditions at the assembly level. For more information on solder reliability, a book by John Lau "Solder Joint Reliability Theory and Application" should be read.

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