Dave,
I appreciate the kind words. I wrote the first version Cracks in the
late 80's and it is still valid today.
John Maxwell
On Wed, 2010-12-15 at 09:29 -0600, David D. Hillman wrote:
> Hi Ioan! Here is a reference that should assist in your efforts:
>
> Cracks: The Hidden Defect by John Maxwell
>
> http://www.avx.com/docs/techinfo/cracks.pdf
>
> John Maxwell's paper is one of the references I show all new engineers as
> a great summary of capacitor cracking root causes.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
> Ioan Tempea <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 12/15/2010 09:08 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Ioan Tempea <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] Intermitent capacitor
>
>
>
>
>
>
> Dear Technos,
>
>
>
> We see intermittence in the functioning of 1206 ceramic caps after
> mechanical assembly. Everything OK in Test, prior to assembly. Due to
> mechanical constraints, the board is rather roughed up during integration,
> so I was not surprised with the issue. But now the things get complicated:
> if the caps are touched up, the intermittence goes away and everything
> works again. So we've had the capacitors x-sectionned, see images at
> http://ipc-technet.groupsite.com/gallery/17220
>
>
>
> So here come the questions:
>
> · If I am not wrong, I have seen comments on this very forum about
> touch-up of ceramic caps actually fixing internal damage of the component,
> rather than the joints, which is misleading and just a temporary fix, the
> cap will stop functioning in a short while. Do I see it right?
>
> · Although there is an 0603 in close neighbourhood of the problem
> 1206, see image, the damage is only on the 1206. Am I wrong considering
> this normal, bigger size, higher bending, more damage?
>
> · The lab couldn't find anything wrong, neither in the joints, nor
> internally in the part. I see a dark line at the interface between the
> solder and the part in the right side image; is this normal, or an actual
> crack?
>
> · It seems the plates of the caps are perpendicular to the PCB,
> instead of parallel. This is how they came in the tape, we are not
> flipping them. Would this orientation of the plates make the component
> more prone to internal cracking than parallel?
>
> · There indeed does not seem to be any 45 degrees cracking of the
> ceramic package at the corners (indicative of mechanical stress). Since
> nothing internal has been detected either and the joints were deemed good,
> what else could be the issue?
>
>
>
> Thanks,
>
>
>
> Ioan Tempea, ing.
> Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
> T | 450.967.7100 ext.244
> E | [log in to unmask] <mailto:[log in to unmask]>
> W | www.digico.cc <http://www.digico.cc/>
>
>
> N'imprimer que si nécessaire - Print only if you must
>
>
>
>
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