Do the math to verify your concept, and nominal conductor widths, but do not specify laminate thicknesses. Specify the overall board thickness only. Try using a note similar to this example: X. CONTROLLED IMPEDANCE CONDUCTORS: SUPPLIER SHALL PLACE A REPRESENTATIVE TEST COUPON ON EACH PANEL AND INSURE COMPLIANCE. SELECTIVE ADJUSTMENT OF INDICATED CONDUCTORS IS PERMITTED, AND ARE EXEMPT FROM MINIMUM CONDUCTOR WIDTH REQT (SEE NOTE X). LAYER WIDTH OHMS 1 .019 45-55 2 .012 45-55 Cliff Lamson PCB Design Manager Plexus Technology Group Raleigh Design Center 919-807-8047 -----Original Message----- From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of Luther, Brandon Sent: Monday, April 16, 2001 4:47 PM To: [log in to unmask] Subject: [DC] impedance control specs 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