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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: Tom Donnelly (tquality@gte.net )
Organization:Consultant
Date posted: Sun Jan 3 1:59:31 US/Eastern 1999
Subject: Screening solder workmanship
Message:
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 tquality@gte.net


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Reply:

Subject: Screening solder workmanship
Reply Posted by: Bill Lieb (lieb.william@corona.navy.mil )Naval Surface Warfare Center
Date Posted: Fri Feb 5 14:43:56 US/Eastern 1999
Message:
No, I can not quantify the difference in screening results if the temperatures had been slightly more extreme. But I can say this. First, you are correct in the assumption that the difference would be minimal. But what is more important is that you are not stressing the hardware nearly enough to precipitate workmanship defects in soldered connections. Your temp range is way too small. I can't speak to your temp rate of change since you didn't mention it, but the temp rate of change is AT LEAST as important as the temp range. I need to work in degrees C: your numbers -30F to +60F equate to about -34C to +16C. So your temp range was about 50C. This is too benign to surface defects in soldered electronic assemblies. We in the Navy like a temp delta of around 120C (somewhat less or more would also be OK) with the extremes normally something like -40C and +80C and the temp rate of change something like 10C/minute. Rate of change less than 5C/minute is worthless and greater than 15C/minute can be bad for the hardware. And all of those temps are to be the hardware temps, not just the chamber air temp. Of course, once you correlate the chamber air temp to the hardware temp, you can monitor the chamber air temp (much easier than measuring the hardware temp) "knowing" that air temp of X equates to hardware temp of Y. Hope this helps.


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