Designer Council Members:
I have questions regarding controlled impedance specifications on fab drawings.
We call out a specific layer stackup and trace width along with their associated
tolerances. We also call out an impedance requirement of 50 ohms +/- 10%. Every
fab house we use (domestic and overseas) asks for a slight deviance, either in 
the stackup or the trace width in order to meet the 50-60 ohm requirement. Every
request is slightly different among all our vendors, based on their materials 
and processes. My questions:

1) Is it worth bothering to draw and dimension the stackup diagram and call out
   the maximum trace widths?
2) Would it be better to just have a note that calls out the required impedance
   and tolerance and let fab houses do the stackup as they need to?
3) Has anyone else out there experienced this problem and how did you solve it?
     Thank you - Alexis Hetrick - Allied Telesyn Int'l. - [log in to unmask]