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June 2000

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Subject:
From:
"Ingemar Hernefjord (EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 13 Jun 2000 12:21:55 +0200
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Hi Steve, what became of your piezoelectric "microphones"? /Ingemar

-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: den 31 maj 2000 00:20
To: [log in to unmask]
Subject: [TN] Capacitor issues...


Hi All!

This is a weird one. We've been building a board for a customer for quite
some time now. Hadn't had a problem since until recently (after going through
some ECO's). Customer thinks we've got a bad batch of capacitors. They're a
ceramic 1206 that's reflowed on, the dielectric is a X7R, and is placed by a
Phillips Topaz. I've looked at the cap under a microscope and don't see any
evidence of fractures. The cap in question is in the center of a .031" board,
and is in a scored 6-up panel.

The customer says they can tell when there's a bad cap on the board, by
putting it on a test fixture and putting finger pressure on the cap and
watching for the value to change for the capacitor. If it changes, it's bad,
if it doesn't, it's good.

Does that sound like a good test? The reason I ask is because I've read on
one of KEMET's web page "Knowledge Edge" articles that dielectrics such as
X7R are considered ferroelectric dielectrics, and have a common
characteristic of piezoelectricity, so by putting pressure on the cap it is
going to change the values, won't it?

Just trying to understand...

-Steve Gregory-

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