Marvin :
I just finished a rather lengthy evaluation of the eddy current devices
available for measuring thin films.
In a nut shell the most accurate  unit ( and there is a difference between
units ) resulted in the following :
        Precision and error of any single reading: +- 0.0001965"
        Instrument Accuracy 0.000886" to 0.0008942" on a 0.000889" standard
        Total instrument error =< 0.0009497"
So you can see that in the thin range the results are questionable. If you
were measuring coatings on the order or 2 mils or greater the instrument
error decreases sharply.
At the thicknesses for Liquid resist Copper and dielectric thickness have an
influence. Set up zeros based on the different cores you run. and if you
read 20 times in the same spot with actual core material as base then the
avg. reading will be close.
The most accurate ways are with and x-ray or laser   . both of which are
considerably more money than an eddy current device.
There is always the good old way of X-Section.


 ----------
From: marvin v. picardal
To: [log in to unmask]
Subject: [TN] THICKNESS MEASUREMENT OF LIQUID RESIST
Date: Friday, March 03, 2000 3:20PM

Dear technetters,

Hi all.  While I am busy performing my evaluation for the
detection & identification of contamination on metal surface,
I have another question.

Is there any other method of measuring thickness of liquid resist on
a surface aside from break test or scraping?  Please help.

Thanks in advance.

Marvin

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