2.5 GHz.......wow. That's up there for FR-4. Hope it's all
Digital. Many things play into a design this far up in
frequency. You may want to consider the following:

1)Design the PCB with Controlled Impedance requirements.
   (#1 Important Thing - This minimizes reflections, mismatches,
        timing issues,...etc.)
2)Use Signal Integrity tools to verify the other PCB attributes
  along with the Zo at that frequency.
  You may consider some sort of spice modeling or see if your design
   software offers and plug in modules for SI analysis.

Here's a few key EMC things from something I'm working on....

 Ground via stitching/fencing (picket/via fence) around the perimeter
 of the PCB and/or critical clocks or signals.
 1st plane in should be a ground (To EMI seal off assembly)
 Face ground planes towards "hot" clock lines if possible.
 Mount PCB with metal screws and standoffs that connect to
 chassis grnd to the assembly enclosure.
 Reduce PCB size and group together and segregate
 critical high-speed circuits.
 Reduce critical line length if possible.
 Reduce lead inductance to high frequency critical components.

I searched for the resistance equation in my archives and it seems to
have been misplaced. :/
The .010" LW @ 1 oz @ 12" long = ~.679 Ohms
The .0085" LW @ 1 oz @ 12" long = ~.799 Ohms

Good Luck,
David Hoover
Field Application Engineer

(PS-Tell us somemore about the logic. RF vs Digital vs Analog)

-----Original Message-----
From: Yanuszewski, Ron [mailto:[log in to unmask]]
Sent: Thursday, September 09, 1999 6:10 AM
To: [log in to unmask]
Subject: [TN] Signal Integrity
Importance: High


All:

We are working a new design that needs to perform at signal speed of up to
2.5 Gh.  The electrician has the following parameters for the design:

*    Material - High Tg FR4.
*    Edge coupled differential pairs .010" line/.010" space/.010" line in a
stripline construction.  Impedance is 100 ohms.  Length of
      these lines may be up to 12.0".
*    1 oz copper for signal layers, 2 oz for plane layers.
*    Because of skin effect concerns the only thing to be adjusted is the
dielectric thickness.

Space constraints may dictate that the line and space need to change to
.0085" line/.0115" space/.0085" line.

My question is will the reduced line width still work or will the skin
effect increase the resistance to a point of disrupting signal integrity.
Also, not beings an electrical person, how do I calculate.

Thanks,  Ron Yanuszewski

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