FW: [SI-LIST] : Broadside v edge coupled striplines

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From: Heard, Chris (cheard@cereva.com)
Date: Sun Jan 21 2001 - 17:01:18 PST


Keeping Broadside pairs on Cores only is not practical in dense designs. A
20 layer construction only has 3 transmission line constructions available
for Broadside routing. Broadside 50 ohm constructions always end up thicker
than edge-coupled, which drives thickness up and total available layer count
in a given mechanical design down. Increased thickness makes manufacturing
engineers angry and less layers makes pcb layout folks angry.

If you don't have too many diff pairs, either way works. If your design has
a large quantity of diff pairs, broadside will make you crazy.

Broadside on backplanes is a bad choice for similar reasons. Cores aren't
available at every construction, increased thickness drives up plated
through hole capacitance which dominates connector signal integrity. Wide
lines with low skin effect are difficult to use because achieving 100 ohms
differentially requires thicker construction...and on it goes.

Chris

-----Original Message-----
From: Scott McMorrow [mailto:scott@vasthorizons.com]
Sent: Saturday, January 20, 2001 2:17 AM
To: Ron Miller
Cc: Aubrey_Sparkman@dell.com; ldmiller@rhapsodynetworks.com;
ribrooks@nortelnetworks.com; SI-LIST@silab.eng.sun.com
Subject: Re: [SI-LIST] : Broadside v edge coupled striplines

Ron,

I would agree. Just trying to dispel the blanket statement that
broadside should be avoided due to manufacturing issues. There
are ways to engineer a board and reduce the tolerance issues
with broadside traces. Trace density is, of course, a seperate
issue.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

Ron Miller wrote:

> Hi scott > > Broadside lines require more real estate than edge coupled > lines. If you have the real estate that is good. We do not. > > If you disagree the contention that broadside requires more > real estate please e-mail me and I will fill in the details. > > ron Miller > > -----Original Message----- > From: Scott McMorrow [mailto:scott@vasthorizons.com] > Sent: Friday, January 19, 2001 10:00 AM > To: Aubrey_Sparkman@Dell.com > Cc: ldmiller@rhapsodynetworks.com; ribrooks@nortelnetworks.com; > SI-LIST@silab.eng.sun.com > Subject: Re: [SI-LIST] : Broadside v edge coupled striplines > > Aubrey, > > The manufacturing issues can be reduced by constructing the > broadside pair on core material and keeping the spacing between > the pairs small compared to the spacing to the planes. Then the > separation between the pair is well controlled and the fields are > well contained between the pairs. > > Another solution which works quite well is to use CPW or > grounded CPW construction for diff pairs on outer layers. > > regards, > > scott > > -- > Scott McMorrow > Principal Engineer > SiQual, Signal Quality Engineering > 18735 SW Boones Ferry Road > Tualatin, OR 97062-3090 > (503) 885-1231 > http://www.siqual.com > > Aubrey_Sparkman@Dell.com wrote: > > > Thanks for that correction. Isn't the difference is really in > > manufacturing, not physics? An EDGE-coupled diff pair is more uniform > > because the pattern is etched in the same process. The BROADSICE-coupled > > diff pair is etched at two different times and additionally has to be > > mechanically aligned for lamination. This adds two additional error terms > > to the accuracy of your BROADSICE-coupled diff pair that the EDGE-coupled > > diff pair does not have. So IMHO, you should really have a packing density > > problem before you consider using BROADSICE-coupled traces. > > > > But if you are doing work for Compaq or Sun, you should use > > BROADSICE-coupled diff pairs whenever possible. :-) > > > > Aubrey Sparkman > > Signal Integrity > > Aubrey_Sparkman@Dell.com > > (512) 723-3592 > > > > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. > si-list archives are accessible at http://www.qsl.net/wb6tpu > **** > > **** To unsubscribe from si-list or si-list-digest: send e-mail to > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. > si-list archives are accessible at http://www.qsl.net/wb6tpu > ****

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