[SI-LIST] Re: Microstrip/Stripline
- From: "Eric Bogatin" <eric@xxxxxxxxxxxxxxx>
- To: <art_porter@xxxxxxxxxxx>, <Charles.Grasso@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 20 Dec 2005 22:22:23 -0600
Hi folks-
As we often point out in this forum, every design is custom, and we can't
really use "rules" that can universally apply to every design, equally well.
Every design has a different set of tradeoffs to balance.
When it comes to microstrip vs. stripline, we can't say, one is better than
the other- all the time. All we can do is point out some of the differences,
and each user can use this as ammunition to determine the best
cost-performance-risk trade off for their application.
Further, we can illustrate some of the methods to perform the analysis so
that any engineer can do the same analysis for their specific applications,
without having to rely on the "opinion of an expert".
For differential pairs, microstrip does provide a tighter pitch, thinner
dielectric and lower attenuation per length than a comparable line width
pair in stripline. Of course, there are also some disadvantages with
microstrip over stripline, such as the greater difficulty of tolerance
control and the fewer number of traces that can fit on the surface compared
to buried into multiple layers.
For single ended traces, another disadvantage of microstrip, as Charles is
alluding to, is the potential for excessive far end cross talk.
In 50 ohm microstrip and stripline single ended transmission lines, with 5
mil wide lines, the near end cross talk in stripline is actually larger than
in microstrip for line spacings less than twice the line width. While, near
end cross talk is lower in stripline than microstrip when the spacing is
larger than twice the line width.
You don't need me or anyone else to tell you these properties. You need an
accurate, easy to use, 2D field solver available to you, to tell you these
things. Then you can set up the problem exactly the way you need for your
specific application.
While we can quantify the differences between microstrip and stripline
performance using a 2D field solver, everyone is going to come up with a
different metric of "goodness" because everyone will have a different
weighting factor for each of the performance metrics and what "good" means
to them.
If anyone is interested in the techniques of exploring design tradeoffs with
a 2D field solver, I have a number of feature articles and columns available
for free download from my web site, and, of course, this topic is covered in
detail in my book and our online lectures.
There is still about 10 days left to take advantage of Polar's sponsorship
of the free viewing of OLL-130, stack up design with a field solver.
Comments on these materials are always welcome- feel free to drop me a note
off line.
--eric
**************************************
Dr. Eric Bogatin
www.BeTheSignal.com
Signal Integrity on-demand training
26235 w 110th terr
Olathe, KS 66061
v: 913-393-1305
f: 913-393-0929
c:913-424-4333
e:eric@xxxxxxxxxxxxxxx
Signal Integrity-Simplified
Prentice Hall, 2004
****************************************
> -----Original Message-----
> From: art_porter@xxxxxxxxxxx [mailto:art_porter@xxxxxxxxxxx]
> Sent: Tuesday, December 20, 2005 11:49 AM
> To: Charles.Grasso@xxxxxxxxxxxx; eric@xxxxxxxxxxxxxxx; si-
> list@xxxxxxxxxxxxx
> Cc: susan@xxxxxxxxxxxxxxx; mark_robinson@xxxxxxxxxxx
> Subject: RE: [SI-LIST] Re: Microstrip/Stripline
>
> 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).
>
> 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.
>
> Art Porter
> Agilent Technologies
>
> -----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.=20
>
> 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.=20
>
> 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.=20
>
> 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.=20
>
> ***************************************
> 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>=20
>
> 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.=3D20
>
> Jeff Loyer
>
>
>
> -- Binary/unsupported file stripped by Ecartis --
> -- Type: application/ms-tnef
> -- File: winmail.dat
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at: =20
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
> =20
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
