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

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From: Zabinski, Patrick J. (zabinski.patrick@mayo.edu)
Date: Tue Apr 03 2001 - 04:24:03 PDT


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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