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Re: [BP] Recommended material and connectors



Ayal-

What Brian failed to state is the most basic of problems with regard to this problem. When we do twisted pair or fiber transmission PHY standards we target them at transmission over well-specified standardized media.

No such luck with backplanes.
The equivalent standards for materials and transmission paths did not exist when P802.3ap started.

I don't know if that situation has improved in the meantime but, even if it has, there is a lot of catching up to do.
My guess would be that things haven't improved much because of Brian's statement:
·         The standard will not specify or even recommend particular connectors, materials or construction methods.


I hope this helps.

Geoff

At 11:33 AM 8/22/2005 , Brian Seemann wrote:

Hi Ayal,

 

You have asked a very simple, reasonable question.  The amount of time and energy that the 802.3ap contributors spent on this is staggering.  But over the past several years, we have learned a great deal about the role of materials and connectors in high speed signal integrity.  A large amount of this work has been contributed in IEEE 802.3ap.

 

Here are some points that address some aspects of your question:

·         In general, the industry has moved forward significantly in what can be done with mainstream materials, connectors and manufacturing processes.

·         The IEEE 802.3ap standard specifies the performance of the transmitter and the receiver.  This is what will ultimately determine the channels servable by the standard.

·         The channel model (Section 69.3) is informative only, to give guidance to backplane builders for what will likely work and not work with the transceivers.

·         The standard will not specify or even recommend particular connectors, materials or construction methods.

·         Careful layout design techniques are probably the most performance-effective and the most cost-effective measures to ensure signal integrity.

·         There are 10Gbps-capable connectors available from several manufacturers.

·         The performance of good connectors can be completely obscured by poor layout design methods.

·         There are multiple contributions showing successful 10Gbps performance on materials such as Nelco 4000-13, Nelco 4000-13SI, and Isola FR408.  Again the standard will not make any recommendations about materials.

·         In many cases on the line cards, lower grade (higher loss) board material (such as 4000-6) has actually been shown to be preferable to higher grade (lower loss) material.  This is because higher loss can reduce the Q (reflection effect) of stubs.

·         The performance of good material can be completely obscured by poor layout design methods.

·         Vias from top layer traces are probably the most disruptive layout feature to signal integrity.

·         Backdrilling vias to eliminate the stub is viewed by many manufacturers as cost feasible.

 

Others on this reflector can weigh-in with more insightful or alternative perspectives.

 

Brian Seemann

 

 

From: Ayal Lior [mailto:Ayal.Lior@tera-chip.com]
Sent: Monday, August 22, 2005 8:54 AM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: [BP] Recommended material and connectors

 

Hi,

 

I am new to this reflector and have a very basic question.

 

We would like to know what is the recommended material and connectors for backplane to drive the 10GBase-KR.

Target application is chassis with maximum length of 40" with two connectors.

 

Any feedback is appreciated.

 

Thanks,

 

Ayal Lior