[SI-LIST] Re: Thick vs. thin diff. pairs
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: <Mark_Burford@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 20 Nov 2006 11:12:52 -0800
My comments below, under your original questions, preceded with >>.
Disclaimer:
The content of this message is my personal opinion only and although I
am an employee of Intel, the statements I make here in no way represent
Intel's position on the issue, nor am I authorized to speak on behalf of
Intel on this matter.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Mark Burford
Sent: Monday, November 20, 2006 8:15 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Thick vs. thin diff. pairs
Dear all,=20
I would like to ask opinions, on the merits and disadvantages of using
wide or narrow microstrip lines.
From where I am sitting it looks like narrow microstrip diff. pairs have
it won hands down.
=20
Thick lines:
More area...which gives more dielectric loss as dielectric loss over
takes skin effect losses at higher frequencies.
>>My sims showed that you'll want wide traces to reduce loss. See my
article at:
http://www.pcdandm.com/pcdmag/mag/0605/0605pcdm_digital.pdf
More S11 because any corner on the line will give a greater area and
more capacitance.
>>Not an issue at current frequencies, as others indicate.
Thicker substrates to keep the impedance at the right value.
>>Yep, and wider traces do this too. Unfortunately, thicker substrates
give more crosstalk, too (assuming distance between traces is held
constant).
As thicker microstrip lines go round a bend, the inter-pair skew will be
more than for two narrow lines.
>>Depends on pitch, not width (though obviously, narrow lines will
probably be at a tighter pitch); not a big issue for current speeds, and
can be accomodated.
There is also the possibility of increased EMI from thicker substrates
(been reading antenna design books).
>>I don't think this is an issue - I'm with Ritchey on this one; haven't
seen a system fail EMI yet because of radiation from microstrip traces.
=20
So please someone tell me why should we use thicker lines? And also
please could someone tell me the trip ups of HDI (high density
interconnect) such as how small can one realistically go with back plane
and inter-chip routing?
=20
Thanks
Mark
=20
=20
=20
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=20
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