For OL, you can use an eddy current tester or something similar.  We use
a couple of different tools from CMI.  You can reach them at
http://www.cmiinternational.com/

For IL, you could put a resistance coupon on the board.

Lee Ritchey includes a nifty little trick in his High-Speed PCB and
System Design Course.  He calls it a stacking stripe.  I'll assume he
won't mind my posting it here in exchange for a plug to take his course
(last I looked it was offered through the Continuing Education in
Engineering, University Extension at University of California, Berkeley
- Go Bears!)  He places a strip of copper 50 mils wide by 200 mils long
on layer 1.  On each successive layer, the strip is 25 mils longer.  The
strip is placed so that the centerline of the 50 mil width will be on
the finished card edge.  When the board is routed, the strips are
exposed and can be inspected without microsection.  It looks something
like this for a 4-layer board.

Layer 1  _______
Layer 2  __________
Layer 3  _____________
Layer 4  ________________


The correct order of layers and copper weights can be verified this way.
He even includes a trace of a specific width so that proper etching can
be verified.  Please note that this is contrary to the typical
requirement to avoid exposing copper on the card edge.  If you use this,
you'll probably need to specify that exposed copper is acceptable in the
stacking stripe area of the card.   Obviously the stacking stripe needs
to be isolated from functional circuits and planes inside the card.

        ----------
        From:  Brian Gaynor [SMTP:[log in to unmask]]
        Sent:  Tuesday, September 14, 1999 12:53 AM
        To:  [log in to unmask]
        Subject:  [TN] Measuring copper thickness @ incoming inspection

        Hi,
        What devices or techniques do you know of that can measure the
thickness
        of external & internal copper on a PWB from a PWB Manufacturer
that does not
        involve micro-section?

        Best regards,
        Brian Gaynor
        Artesyn Technologies Europe.
        [log in to unmask]

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