on Thu, 15 Aug 1996 15:10:15 -0400 
[log in to unmask] (Howard Feldmesser) asked :

>        A vendor recently received back from us a batch of multilayer
>ceramic chip capacitors that failed their dissipation factor specification.
>They claimed that the parts were merely aged and put them through a
>"de-aging" process, apparently a vacuum bakeout.  The parts now meet the
>spec!  Does anyone have any idea what the process is and what it does?  How

De-aging of ceramic capacitors is a bake above their Curie point
temperature.  I've had to bake caps anywhere from 1 to 16 hours to de-age
them.  No vacuum is involved.

>long will the parts remain "de-aged?"  What about parts already installed;

As soon as they are cooled they start the ageing process.  All parts with
the same dielectric formulation should age similarly.  Your cap vendor
should be able to give you the ageing characteristics for your parts.  It is
expressed in % percent per decade, with each decade being a power of 10
hours.  DC voltage can also accelerate the ageing process (did you do a DWV
test before you measured DF??).  I'm familar with capacitance ageing
characteristics, not DF - the dielectric loss decays with time also which I
take to mean increases(?).  So perhaps DF increases at the same rates as the
capacitance changes.  Capactitance ageing examples - class I ceramics
(NPO-COG)  0%/decade; Class II(BX-X7R) -3%/decade, (Z5U) -4%/decade.  YMMV

>does D increase with age on all parts?  Do you have any citations in the

C/DF ageing depends on the dielectric used.

>literature?  Can the de-aging process work on humans?

Hmmmmm.  There's supposed to be a fountain somewhere for that....

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