Tamir
I have had the opportunity of designing boards at that frequency.
There are several factors to take into account
1- are these High speed signals path long or short
if so you can use FR4 but keep in mind that you may get Signal loss if
your traces are to thin, but as your traces get wider, your board
thickness will increase as you meet the desired impedance.
I routing the High speed signals turns out not being that long, then a
thin trace would not be as bad.
I designed a back Plane using Hi temp FR4 18 layers running 3.5GHz
Differential signals 100 ohms Diff.
the trace width I used was 8 mils stack up was
Plane
10
signal
16
Plane
the overall Board thickness was at .240"
I used the TDR to measure the Impedance of the Signal traces and compare
my results with the report from the Fab shop
all signals were in the range of 97 -100 ohms diff as expected.
Then we tested and measure the Back Plane with Traffic running through
it.
The signal quality was very good overall, with very little loss.
2- Another thing into consideration is to take into account the Max
board thickness you will be using
if a smaller valued is desired, you may have to use a different
material, that would meet the desire impedance, If I was in your shoes,
I would consult the Fab house you currently use, they will probably have
several option for You.
Regards
InkraNetworks
Patrick Jabbaz
Sr Board Layout Eng.
40971 Encyclopedia Circle
Fremont, CA 94539
Work (510) 249-4835
Mobile (408) 621-6533
[log in to unmask]
-----Original Message-----
From: Tamir Ben Shoshan [mailto:[log in to unmask]]
Sent: Thursday, December 13, 2001 7:56 AM
To: [log in to unmask]
Subject: [DC] High frequency PCB
Hi,
I need an urgent help for details about the raw materials used for
3.5GHz PCB. The estimation is that the board is going to be 22-32 layers
with control impedance requirements, it probably includes blind/buried
via.
If anyone have some experience working with that kind of designing I
would appreciate getting the design rules for the editing art work(trace
width, thickness and space), how does the via effect the impedance or is
there any calculation for knowing that influence. For that purpose I
need some details on the Dielectric Constant behavior of the raw
material with reference to the frequency.
I’ll be happy to discuss that issue with anyone who already designs that
kind of board type or anything similar.
Best Regards,
Tamir B. Shoshan
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