[SI-LIST] Trace skew matching, common mode conversion and laminate weave ... oh my!

From: Scott McMorrow <scott@xxxxxxxxxxxxx>
To: silist <si-list@xxxxxxxxxxxxx>
Date: Fri, 21 Jan 2005 11:20:26 -0500

All,
Since DesignCon 2005 is fast approaching, I thought I'd bring up a 
technical topic that is near and dear to my heart.  The last few years 
on this list, we have discussed various aspects of FR4 laminate 
properties and their effect on trace propagation.  Well, having been 
"bit" a few times by unexpected skew caused by trace/weave allignment  I 
would like to ask others to share their "experience, strengths and hope" 
on this subject.

How close do you think it is possible to match the bus skew on epoxy 
fiberglass laminates?
How close to you think you can match differential skew on epoxy 
fiberglass laminates?
What do measurements tell us about laminate weaves?
Are there methods to alleviate weave created skews?
Have the methods been patented?

This year, Chris Heard from Teradyne and myself will be presenting a 
paper at DesignCon that may be of interest and will cover these topics.  
The answers are quite surprising and may very well change your views on 
this topic and on the topic of bus timing closure.

4-TP2
The Impact of PCB Laminate Weave on the Electrical Performance of 
Differential Signaling at Multi-Gigabit Data Rates
Tuesday, February 1 | 2:50pm - 3:30pm

Scott McMorrow, Director of Engineering, Teraspeed Consulting Group
Chris Heard, Hardware System Architect, Teradyne Connection Systems

Variation in performance for laminates will be characterized and 
compared, to provide a framework for the worst case understanding of 
material influences on differential pair signaling. Measurements of PCB 
laminate weaves are made showing the variation of Er, loss Tangent and 
delay of traces in commonly used stackup configurations, for various 
material types, including FR-406 and Nelco 4000-13SI. These comparisons 
will be used to show designers the hidden impact of substrate material 
choices on design parameters such as: Er, loss, impedance control and skew.


regards,

scott

-- 
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed is the registered service mark of 
Teraspeed Consulting Group LLC



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[SI-LIST] Trace skew matching, common mode conversion and laminate weave ... oh my!

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