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From: whit3rd on 3 Apr 2007 17:32
On Apr 1, 3:54 am, Adam S <not.valid(a)nosuchaddress> wrote:
> I was wondering what happens when you put too much voltage across a one
> of those low voltage multilayer ceramic capacitors. I took a 2.2uF 10V
> X7R in 1206 package, and applied 95V across it and nothing exciting
> happened. Leakage settled to 0.5uA

> I noticed was capacitance had dropped from 2.30uF to 1.85uF

The X7R and BK (and some other) capacitor ceramics are nonlinear
(actually ferroelectric), and the problem with overstress isn't
leakage or explosion. It's capacitance-value-droop. And as you
saw, the value stays out-of-spec after the stress is removed.
At 95V, if you'd measured it (put a known-good capacitor in series
and voltage-stress it then measure the series pair under voltage),
you might have found 0.2 uF.

A buddy of mine was trying to measure capacitors for a filter. He
never got the same value twice from the digi-bridge. I saw the
markings on the capacitor and laughed- it was the heat from his
fingers
as he handled the caps that made 'em always a few percent off
on successive measurements. Nonlinear materials are great for
energy density and in applications when you care little for AC
dissipation. They don't really obey the straight capacitance equation
very well, though.

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