Good Day!
  We are having a raging debate about specifying controlled impedance on our
fabrication drawings.
  The main part of the debate is over laminate thickness specifications.  I
would like to know how other companies are handling these issues.
        Are you specifying the individual laminate thickness?
        Are you specifying the individual laminate thickness tolerance?   If
so, how do you handle deviations between different fab houses beyond the
tolerance?

It seems that every time we use a different fab house, they like to use
their standard laminates.  While this is also a benefit to us, it causes
problems when our boards are microsectioned and the board doesn't agree with
the print.

We will continue to specify trace width, copper thickness and impedance, all
with tolerances.

Any input will be appreciated!

        Brandon Luther
        Dataram Corp.
(609) 799-007  x2310