You may look for my reliability column on this issue in the May issue of Global SMT & Packaging magazine.
Werner

 


 

 

-----Original Message-----
From: David D. Hillman <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Apr 8, 2011 12:03 pm
Subject: Re: [TN] Cracked ceramic capacitors


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

Please respond to

TechNet E-Mail Forum <[log in to unmask]>; Please respond to

"Rivera, Raye" <[log in to unmask]>





To

<[log in to unmask]>

cc



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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