[SI-LIST] Re: Microstrip/Stripline

I agree with this.  When we needed a transmission line with a bandwidth
from DC to 20 GHz, we built it in microstrip.  However, we had to put very
rigid constraints on plating.   It was possible to do this because we only
needed one per PCB.  It would not have worked if we needed 2000, which is
often the case with backplanes and switch fabrics.

Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX-    707-568-3504

I just used the energy it took to be angry to write some blues.
Count Basie


> [Original Message]
> From: Eric Bogatin <eric@xxxxxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Cc: <eric@xxxxxxxxxxxxxxx>; <susan@xxxxxxxxxxxxxxx>
> Date: 12/18/2005 4:41:41 AM
> 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. 
>
> 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. 
>
> 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. 
>
> 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. 
>
> ***************************************
> 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> 
>
> 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.=20
>
> Jeff Loyer
>
>
>
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>
>
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