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March 2007

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Subject:
From:
"Gregg A. Owens" <[log in to unmask]>
Reply To:
Gregg A. Owens
Date:
Fri, 16 Mar 2007 11:58:30 -0700
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text/plain
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text/plain (60 lines)
Dear Werner:

MIT the university is in Cambridge, however us Master IPC Trainers are all around you....

Gregg

-----Original Message-----
>From: Werner Engelmaier <[log in to unmask]>
>Sent: Mar 16, 2007 11:53 AM
>To: [log in to unmask]
>Subject: Re: [TN] SMT Solder Joint Strength
>
>Hi Gregg,
>Last I looked MIT was in Cambridge.
>Solder joint strength is never the issue with a properly 'wetted' solder 
>joint. Under sufficient force you will rip the soldering pad out of the resin 
>matrix, but not separate the solder joint.
>The strength, or more accurately the yield strength, comes into the picture 
>when thermal cycling, because the yield strength is highly 
>temperature-dependent [as are almost all other properties of solder].
>When T-cycling leadless solder joints the cyclic stress range will be bounded 
>by the yield strength of the solder at the prevailing T; the reason why 
>compliant leads work is that they do not allow the stress range to come close to 
>the yield strength=f(T).
>The high variability of lead geometries, and some of the above, make SJ 
>strength standards impractical to say the least, and even if you could do it, what 
>would you do with the information?
>What is much more important is the failure mode—either brittle interfacial 
>showing   there is something wrong with the SJ arrangement, or pad rip-out 
>meaning the SJ is good.
>
>Werner
>P.S.: Bev, which part of the above do you disagree with?
>
>
>
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