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Subject:	Re: Strain impact on reliability?
From:	Robert K Veale <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Thu, 27 Jan 2000 15:52:05 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (44 lines)

I have studied the effect of PCB flexure on the cracking of MLCs.  This
failure mechanism is
widespread throughout the industry and can lead to latent failures.  For
normal case sizes
in the worst orientation,  a microstrains of about 1300 are in the danger
zone for cracking the
ceramic body (not the solder joint).   Trying to apply this number is
problematic since
predicting how much flexure the PCB will see is difficult.  Check out
Murata's application
note on this subject.

Bob Veale
Rockwell Automation

Breton Flemming writes
"I am involved in a project with the objective of understanding effects
of PCB surface strain (due to flexure) on component reliability.
Throughout my research, I have encountered studies surrounding global
effects of warpage and flexure on product reliability, but have not
found values indicating maximum stress/strain thresholds for individual
surface mount components.  The advantage of such information would be to
give general ideas about component placement issues on any board, not
just one particular size or geometry.
Any direction as to possible sources of information relating to
individual component stress/strain thresholds (studies, books, articles,
etc.) would be greatly appreciated along with any thoughts or comments.
Any surface mount components are of interest for any one of the
following failure mechanisms:  yield, creep, fatigue."

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