RE: [SI-LIST] : RE: 2.5 GHz in FR4

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Tue Apr 03 2001 - 10:20:02 PDT


This is quite masochistic. Do you have to do it to yourselves and use FR4,
unless you are running couple of inches of hi-speed wires?

-----Original Message-----
From: Larry Miller [mailto:ldmiller@rhapsodynetworks.com]
Sent: Tuesday, April 03, 2001 12:57
To: 'Gaboian, Jerry'; 'Zabinski, Patrick J.'; si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : RE: 2.5 GHz in FR4

I, too, must take issue with practically every statement made by Mr.
Zabinski.

We are using stripline. We do not have vias except the connector pins (AMP
HS-3).

We are using 10-mil stripline traces on the backplane, 5-mil stripline on
the plug-in boards (have to, the boards get too thick otherwise). Yes, the
5-mil sections are lossy because of skin effect; luckily, these are short.

We have backplane traces that are over 12" long (can't help it).

In spite of all this, our system happily percolates along at 3.125 GHz (2.5
GHz with 8B/10B coding).

Larry Miller

-----Original Message-----
From: Gaboian, Jerry [mailto:j-gaboian@ti.com]
Sent: Tuesday, April 03, 2001 5:00 AM
To: 'Zabinski, Patrick J.'; si-list@silab.eng.sun.com
Subject: RE: [SI-LIST] : RE: 2.5 GHz in FR4

Check out this site from AMP.....

It will surprise you on how long of a trace one can use.....
They also compare other materials, widths act.....

http://www.amp.com/simulation/files/papers/dc99cmdh.pdf

Regards,
Jerry

-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@mayo.edu]
Sent: Tuesday, April 03, 2001 6:24 AM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : RE: 2.5 GHz in FR4

Sreejith,

It is possible to use common FR4 in 2.5 GHz systems, but you
need to follow a few design constraints:

* Do not use stripline. The discontinuities presented by
the vias are most often killers. Avoid all vias in the high
speed nets and use microstrip (i.e., top-surface only).

* Use wide traces. FR4 is lossy at 2.5 GHz, so try to compensate
for the high dielectric loss by decreasing the metal loss. Use
wider traces which will reduce the resistive losses in the metal.

* Use short traces. If you need to route 2.5 GHz signals
on nets that are 10 inches (25 cm) long, I doubt if your
system will function. Keep the traces *short* (say, less
than 1 inch [2.5 cm]).

Hope this helps,
Pat

> HI All,
>
> i am doing a 2.5Ghz PCB design. i was wondering whether FR4 material
> is sufficient for such high speed signals? or i should look at some
> other material for these desings? and if FR4 is sufficient is
> there any
> special care i have to take (other than impedance matching
> and differential
> routings)
>
> thanks in advance,
> Sreejith
> Paxonet Comm. (I) Ltd.
> Blore, India

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