Aging of ceramic capacitors is real.  This phenomena is more pronounced in higher K dielectric
capacitors such as Y5V or Z5U. Reflow temperature profiles will (at least partially) de-age the
 capacitor since it will take the ceramic above the Curie temperature. For a more detailed
discussion see   http://www.novacap.com/DielectricProperties.pdf

Bob Veale
Rockwell Automation
Cleveland Ohio





Martin Christie <[log in to unmask]>@IPC.ORG> on 02/01/2000 03:42:00 AM

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

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:
Subject:  [TN] Ceramic chip capacitors


>
>Technet guru's,
>
>We have a problem with a 1uF 10v -20/+80% (0805) chip capacitor. We have
>seen some failures at in-circuit test for low capacitance (much less than
>the -20% tolerance). Some of our test operators have found that by
reflowing
>(hand flowing) the component they can bring it back into tolerance. I've
had
>some of these components micro-sectioned and on one particular example,
have
>found a crack under the metallisation. After checking components off the
>reel I've found them to be very low, in a lot of cases they were well
below
>the -20% tolerance (I've yet to get some micro-sectioned). I've not ruled
>out the possibility that it could be our placement equipment or thermal
>shock but we haven't found the same failure mode on any other similar
value
>components that we're placing. The reel has now been quarantined and
another
>reel (which is well within tolerance) fitted. I'm still awaiting the
results
>of the next production.
>
>To satisfy my curiosity that it wasn't variation in our meter, I measured
>some (12 in number) similar value components straight off of another reel
>from a different manufacturer. I found that they were within tolerance but
>when measured over a period of 3 hours their capacitance increased by
about
>10% (I confirmed it wasn't our meter by measuring a known value component
>over the same period and found less than 3% variation). After contacting
the
>manufacturer, I was told it was not unusual for reeled capacitors over 2
>years old to exhibit this phenomena (well known in his industry) and that
a
>bake should be undertaken to bring the components up to their nominal
values
>(although he would not comment on the bake parameters). The components
were
>manufactured in 1998.
>
>I and my colleagues (including our Test Engineers) have never heard of
this
>before. Does anyone have any further information on this subject or know
>what the recommended bake is?
>
>Regards,
>Martin Christie

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