Luther,
    We rely on our fabricator to pick the laminates. We specify the
impedance and tolerance (+/- 10%)
for each layer, overall thickness, layer requirements, and etch and spacing.
This works out well for us.

Jim Peterson
Evans & Sutherland
Senior Cad PC Designer
[log in to unmask]
801.588.7210

-----Original Message-----
From: Luther, Brandon [mailto:[log in to unmask]]
Sent: Monday, April 16, 2001 2:47 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

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------