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December 2010

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From:
Stewart McCracken <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stewart McCracken <[log in to unmask]>
Date:
Wed, 15 Dec 2010 18:21:48 +0000
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Hi Ioan,

I think that it's worth re-stating that there is a very high chance that the feature which is highlighted is actually an artefact caused by edge rounding of the sample and viewing using light microscopy. In the first place, you might find it useful to examine the interface at higher magnification in the light microscope. There is quite a lot of relief on the sample and not that this runs roughly parallel to the feature in question at the edge of the device. It is quite possible, that the rounding occurs preferentially in this orientation, effectively "scooping out" a shallow trench immediately next to the device metallisation. Although the edge may be rounded, the shadowing can be reduced by viewing at slightly higher mag (200 - 500x). I wouldn't put too much effort into figuring out what might have created this feature until you conform whether it is in fact it is a defect. If you have access to a SEM, that's definitely your best option as it will also give you feedback on metallurgy. If not, there are plenty of labs who can help - including us!

Kind regards,

Stewart


Stewart McCracken
MCS Ltd.
Centre House
Midlothian Innovation Centre
Roslin
Midlothian
EH25 9RE
 
m. +44(0)7711 541735 
t.   +44(0)131 440 9090
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w. www.themcsgroup.co.uk
 

  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: 15 December 2010 16:38
To: [log in to unmask]
Subject: Re: [TN] Intermitent capacitor

Gallery updated with Richard's interpretation, lines pointing towards a separation line.

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] 
W | www.digico.cc

N'imprimer que si nécessaire - Print only if you must


-----Message d'origine-----
De : Stadem, Richard D. [mailto:[log in to unmask]] 
Envoyé : December-15-10 10:27 AM
À : TechNet E-Mail Forum; Ioan Tempea
Objet : RE: Intermitent capacitor

Ioan, 
I have attached a copy of your picture, and I added red arrows showing the areas where it is apparent that there is a crack or separation between the solder and the endcap. You can add it to the IPC pics if you wish.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Wednesday, December 15, 2010 9:09 AM
To: [log in to unmask]
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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