Wanner,

I have recently seen leaky chip capacitors where the failure was apparently
caused by very small internal cracks between one or two plates.  The cracks
appeared to be caused by sintering defects.  It is not clear to me whether or
not these cracks can be caused by external stress (i.e. thermal or bending).
There were no cracks visible on the external surfaces of the components.  The
carcks do not look like the cracks normally associated with thermal or bending
stresses which tend to cross multiple plates initiating near a termination and
travelling through the stack at an angle.

Ed


Wanner Bernhard wrote:

> Hi Ed
>
> As manufacturer of power supplies we are using also chip cpacitors.
> For years we have had no problems with chip capacitors. The analysis of the
> field returns shows no problem with chip cap's.
>
> Now (since some weeks) we have problems because failing chip cap's.
> This failing chip cap's shows a conductivity like a resistor. There are no
> visible cracks (may be cracks would be visible using a REM).
>
> As a first thesis we assume a problem at a subcontractor because inadequate
> reflow-temperatureprofile (to high reflow temp and/or to high initial
> warm-up rate).
>
> As second thesis the cap-manufacturer could have a problem, because since
> some months the same cap-size is smaller. May be this cap redesign has
> caused this leackage problem.
>
> Because this cap leackage is a real problem for us. I would be very
> interested to get any informations about possible failure mechanism (or to
> hear about the current field/application problems).
>
> Best regards
> Bernhard Wanner (QA Manager)
> Melcher AG, Switzerland
> www.melcher.ch (and also www.power-one.com)
>
>
>         ----------
>         Von:  Edward Hare, <SEM Lab, Inc.>[SMTP:[log in to unmask]]
>         Gesendet: Freitag, 20. August 1999 16:16
>         An:  [log in to unmask]
>         Betreff:   [TN] Chip Capacitors
>
>         Hi all,
>
>         I would like to hear from anyone who can estimate their
> manufacturing
>         yield impact due to failure of chip capacitors, i.e. due to cracks,
>         leakage, etc.  I have been doing failure analysis on these types of
> part
>         issues and I am trying to benchmark expected yield and/or failure
> rates
>         under "normal" conditions.
>
>         Any help would be sincerely appreciated!
>
>         Best Regards,
>         Ed Hare
>         --
>
>                        SEM Lab, Inc.
>         Scanning Electron Microscopy and Failure Analysis
>                        Snohomish, WA
>                        (425)335-4400
>                    http://www.sem-lab.com
>
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