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May 2000

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Subject:
From:
"Kelly M. Schriver" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 1 Jan 1999 18:52:25 -0600
Content-Type:
text/plain
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text/plain (80 lines)
Yo Steve -

First off, "finger pressure" is just about as precise and controlled a
physical test method as no control at all.  Second, the chemical and
electrical properties of the skin surface will vary considerably from one
person to another, and from one moment to another, dependent on which
nostril that finger may have been most recently.

I think you need to gently help that customer understand that these methods
are rather invalid and not repeatable.

Regards - Kelly


-----Original Message-----
From: Stephen R. Gregory <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, May 30, 2000 4:22 PM
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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