[SI-LIST] Re: AW: Fiber weave effect modeling
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 13 Jan 2011 13:31:06 -0800
I don't think the elimination of standard weaves is straightforward. I
wholeheartedly agree that "flat" weaves exist and are a very attractive
solution but, at the time we wrote our paper, they cost about 2x that of
standard material. I don't know if the difference is still that high, but I
doubt it's insignificant.
For many designs, the cost differential is outweighed by the benefits. For
others, it is not. 10 degree routing, ugly as it may appear and as time
consuming as it is, can be attractive if it saves significant money.
On the other hand...
There may soon come a point where bus speeds increase such that it is
impossible to avoid routing parallel to the board edge for problematic
distances. At that point, flat weaves will be a more palatable option. For
instance, just breaking out of a large device plus routing into a connector
might require 2" of length that can't be angled. For a 40GT/s bus, that's
probably unacceptable. Then, the choice gets clearer.
For now, many of us are in the grey area where the option of using flat weaves,
and getting rid of our funky angled routing, isn't clear-cut.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Lee Ritchey
Sent: Thursday, January 13, 2011 10:22 AM
To: Havermann, Gert; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: Fiber weave effect modeling
I recommend you use neither of those weaves with high speed serial links due
to there negative effect on skew. The best weaves are known as "flat"
weaves. The best are 1067 (replaces 106), 1086 (replaces 1080), 2113 and
3313. These are so uniform you don't need to worry about weave effects.
These weaves were developed to make laser drilling blind vias more uniform
and happen to be great for SI purposes!
You also don't need to route your PCBs on a 15 degree angle to the weaves,
which is painful to do and wastes materials, so long as you stick with the
weaves listed above.
Lee Ritchey
--------------------------------------------------
From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
Sent: Wednesday, January 12, 2011 6:31 AM
To: <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] AW: Fiber weave effect modeling
> this is a great paper, many thanks for sharing it with the si-list.
>
> please allow me a question. I understand that the 106 and 7628 Prepregs
> are used to predict the dk values of "pure epoxy" and "close proximity to
> the Glass bundle".
> Do you think that the "pure epoxy" value is always the worst case that I
> have to expect for my diff pair? If I (for instance) would only use 7628
> Style everywhere, will there even be areas "in pure epoxy", or is the
> weave dense enough that the worst dk is somewhere between the calculated
> min. and max. value?
>
> BR
> Gert
>
>
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> Alexander Rost
> -----Ursprüngliche Nachricht-----
>
> Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
> Auftrag von Bert Simonovich
> Gesendet: Freitag, 7. Januar 2011 21:55
> An: si-list@xxxxxxxxxxxxx
> Betreff: [SI-LIST] Fiber weave effect modeling
>
> Hi all,
>
> Recently there were discussions on PCB fiber weave effect. I recently did
> a study and published a White Paper titled, "Practical Fiber Weave Effect
> Modeling".
>
> Abstract:
> Fiber weave effect is becoming more of an issue as bit rates continue to
> sore upwards to 5GB/s and beyond. Due to the non-homogenous nature of
> printed circuit board laminates, the fiberglass weave pattern causes
> signals to propagate at different speeds within differential pair traces;
> causing timing skew and mode conversion at the receiver; leading to
> reduced bit-error-rate (BER) performance; and increased EMI radiation. The
> relative dielectric constant (Dk) surrounding a trace ultimately
> determines its propagation delay. This paper delves into the issue and
> presents a novel approach to practically establish worst case min/max
> values for Dk and use them to model this effect using ADS circuit modeling
> software. A PCIe CEM
> Rev2 case study is used to practically demonstrate the model and to
> explore the design space.
>
> Here is the link: http://lamsimenterprises.com/White_Papers.html
>
> Thanks to Jeff Loyer, Istvan Novak and Gustavo Blando for there help in
> clarifying some results of their prior published work on the subject.
>
> I hope you find it useful.
>
> -Bert
>
> Lambert (Bert) Simonovich
> Consultant and Founder
> LAMSIM Enterprises Inc.
> Web Site: http://lamsimenterprises.com
> Blog: http://blog.lamsimenterprises.com/
>
>
>
>
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