Re: [BP] Recommended material and connectors

[Brian Seemann <brian.seemann@xxxxxxxxxx>]

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

 

 

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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