[SI-LIST] Re: Microstrip/Stripline
- From: <art_porter@xxxxxxxxxxx>
- To: <Charles.Grasso@xxxxxxxxxxxx>, <eric@xxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 20 Dec 2005 10:49:29 -0700
Interesting discussion. The received wisdom here has always been that =
stripline is preferred, for the following reasons:
* Better immunity to external fields, crosstalk, etc.
* Not as good a radiator of EMI
* Don't have to worry about weird dielectric effects of solder mask etc.
* Less sensitive (though not immune) to impedance variations due to =
width variations due to etch process variations
* Field is better behaved because (A) it is terminated by ground planes =
on both sides and (B) it travels in the same dielectric on both sides. =
Having board dielectric on one side and air on the other can lead to =
increased dispersion (though this is only significant at really high =
frequencies).=20
But Eric makes some really good arguments in favor of microstrip. The =
difference is that we're probably coming at the question from the =
viewpoint of instrumentation, as opposed to laying out dense high-speed =
digital boards for computers, etc. =20
Art Porter
Agilent Technologies=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Grasso, Charles
Sent: Tuesday, December 20, 2005 10:31 AM
To: eric@xxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Cc: susan@xxxxxxxxxxxxxxx
Subject: [SI-LIST] Re: Microstrip/Stripline
Hi Eric - Thanks for the interesting post.
Can you comment on the difference in crosstalk performance
between stripline and microstrip?
Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxx
Email: charles.grasso@xxxxxxxxxxxx;
Email Alternate: chasgrasso@xxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Eric Bogatin
Sent: Sunday, December 18, 2005 5:42 AM
To: si-list@xxxxxxxxxxxxx
Cc: eric@xxxxxxxxxxxxxxx; susan@xxxxxxxxxxxxxxx
Subject: [SI-LIST] Microstrip/Stripline
Jeff and others-
I just finished a study on the stack up tradeoffs for
various differential pair geometries, which will be included
in a new online lecture, OLL-183, to be posted shortly.
While it is true that, as with many of the questions asked
about designs for signal integrity, it depends, there are
some definite tradeoff issues between microstrip and
stripline. In designing the stackup, three important
questions are: the interconnect density possible, the total
dielectric thickness and the attenuation per length, which
influence the ultimate bandwidth of the interconnect and the
highest possible transmitted bit rate.=3D20
Microstrip, wins on all counts. You can build 100 Ohm
differential pairs with a tighter pitch in microstrip than
stripline, with a dielectric thickness that is about a
quarter that of stripline for the same width lines, and with
an attenuation that is 30% reduced from stripline. The
attenuation reduction is dominated by the lower effective
dielectric constant and the lower contribution to the
dielectric loss from the field lines that are in the air.
The conductor losses, for the same line widths are pretty
close, and decrease in significance as you go up in
frequency anyway.
Microstrip is not very efficient for routing many of the
lines, as you have to share the surface with all the
components, but if given the option, it is often a good path
to take. As Lee Richey pointed out, you want to qualify your
fab vendor that they can fabricate quality surface traces.=3D20
As has often been pointed out on this list, it is difficult
to make generalizations and use a set of rules to follow to
design each product the same way since each design has a
different set of tradeoffs. This is why the most important
thing for an engineer to learn is the methodology to
approach solving problems, and then access to the tools to
make you more efficient when optimizing the design of your
product.=3D20
The online lectures posted on www.BeTheSignal.com empower
engineers with the techniques to help you make your own
decisions about your own designs, and move you up the
learning curve to build your signal integrity career.=3D20
***************************************
Eric Bogatin
Bogatin Enterprises
OnLine Lectures on Signal Integrity
26235 w 110th terr
Olathe, KS 66061
v:913-393-1305
cell: 913-424-4333
f:913-393-0929
e:eric@xxxxxxxxxxxxxxx
www.BeTheSignal.com <http://www.BogEnt.com>=3D20
Signal Integrity- Simplified
published by Prentice Hall
*****************************************
Msg: #1 in digest
Subject: [SI-LIST] Re: Microstrip/Stripline
Date: Tue, 13 Dec 2005 10:41:59 -0800
From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
As someone stated, there are any number of topologies for
microstrip that can be made to be more lossy than stripline,
and vice-versa. Using a 2-D solver, I looked for trends and
found that there wasn't any. The very slight trend I saw
was so weak that it reversed itself, depending on whether I
was looking at single-ended or differential signals. And it
was completely overwhelmed by stronger factors, such as loss
tangent, etc.
Contrary to what others have said, I don't remember reading
anything definite reason why one should be more or less
lossy than the other, and that's what I found in my study
(though I too have heard lots of theories otherwise).
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.=3D3D20
Jeff Loyer
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