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April 2011

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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 8 Apr 2011 11:03:25 -0500
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Hi Raye - Here is a link to John Maxwell's paper - Cracks: The Hidden 
Defect - on root causes of cracked capacitors. It is one of the best 
treatments of how our soldering processes can cause cracked capacitors and 
should be required reading for all new engineers. 

http://www.avx.com/docs/techinfo/cracks.pdf

We have found that  visual inspection and/ or thermal cycling will not 
provide the level of detection that you are looking for. We have subjected 
suspect capacitors/assemblies to high temp/high humidity (85C/85%RH) and 
then conducting electrical testing producing better predictive results. 
That conditioning sequence isn't fool proof but worked better for us in 
finding damage capacitors. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Rivera, Raye" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
04/08/2011 09:55 AM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Rivera, Raye" <[log in to unmask]>


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Subject
[TN] Cracked ceramic capacitors






Hello Technetters,

We had an issue with cracked SMT ceramic capacitors causing boards to fail 
functional test. We isolated the problem to a reel of parts that contained 
some cracked caps and purged these. Problem solved.

My question is about what to do with boards built with these capacitors 
before we purged. The boards pass functional test. The concern is that a 
cracked cap was loaded, but has not yet failed. The range of actions 
proposed here are:

- Temperature cycle the boards between -5 C and 55 C a few times. The 
theory is that this will flush out any latent defects.

- Visually inspect for defects.

- Manually change out all the suspect caps, about 50 per board.

Does anyone have thoughts on what would be the best method or another 
idea? We don't have ICT capability.

Thanks!

Raye Rivera



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