I don't whether it's just 2 top layers or more (don't have the actual samples) but the fact that theuy also rack in normal direction to the board (through the layers) seems to rule out a CTE mismatch as the root cause.
Regards,
Vladimir
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Jul 14 11:34:59 2008
Subject: Re: [TN] Ceramic caps
I don't know a great deal about their construction but are you seeing
delamination of two of the multiple layers of the capacitor?
I can imagine CTA mismatch between the PWB and cap causing a difference
in stress between the top and bottom of the cap irrespective of which
way it was aligned to the PWB edges.
Regards,
Igoshev, Vladimir wrote:
> Different locations, identical caps placed along and normal to the board. :-)
>
> Regards,
>
> Vladimir
>
> ----- Original Message -----
> From: Allen Maddox <[log in to unmask]>
> To: TechNet E-Mail Forum <[log in to unmask]>; Igoshev, Vladimir
> Sent: Mon Jul 14 11:19:16 2008
> Subject: Re: [TN] Ceramic caps
>
> Just curious if there is any consistency in the size of the cap or it's place on the board and direction it faces?
> It seems like you've covered all the obvious failures so far.
>
> Allen Maddox, CID+
>
>
> "Igoshev, Vladimir" <[log in to unmask]> wrote:
>
> That was the first thing I asked and was told "No", they hadn't been re-worked or placed manually.
>
> What bugs me the most is that I have a hard time imagining how a top half of a cap can be separated from the bottom one. If it wasn't a manufacturing problem, then how it should have been loaded (mechanically) to crack like that.
>
> Regards,
>
> Vladimir
>
> ----- Original Message -----
> From: TechNet
> To: [log in to unmask]
> Sent: Mon Jul 14 10:39:57 2008
> Subject: Re: [TN] Ceramic caps
>
> In addition to the very good info you have already received, consider
> how the caps are being soldered or reworked. I would check to make sure
> none were soldered by hand using conventional solder irons. Rework such
> as solder touchup should only be done with a hand-held hot air device
> such as a Hakko or JVC.
> Never, ever allow an MLCCC to be soldered with a conventional soldering
> tool, as the sudden thermal shock will crack the body of the connector,
> and/or the large heat transfer can melt the high-temp solder connections
> internally (plate to terminal connections).
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Igoshev, Vladimir
> Sent: Monday, July 14, 2008 8:08 AM
> To: [log in to unmask]
> Subject: [TN] Ceramic caps
>
> Hi TechNeters,
>
> I came across an unusual (at least to me) failure mode of ceramic caps.
> They crack along the component body in either normal (from top all the
> way through to the bottom), or parallel (from one side all the way
> through to the other side) direction to the board the caps are mounted
> on.
>
> Has anyone seen something similar?
>
> Thanks a lot in advance.
>
> Regards,
>
> Vladimir
>
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--
Eric Christison Msc
Mechanical Engineer
Consumer & Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
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