[SI-LIST] Re: 10G Differential routing trace width

Hi,
Your answer depends on the type of dielectric you are using.
So if you are using FR4 dielectric and for distances of 10-15 inch of PCB
routing , dielectric losses dominate over cu skin effect loss. So it might
be better to use 4 mil traces with more spacing to the adjacent pairs to
reduce the crosstalk.


> Thanks for all your answers! I think I will have to run a couple of
> simulation to get the answer in my case. In term of dielectric. We
> actually use FR408-2113 and my guess is that it's close to be the best we
> can get for a small amount of money. I know that there's better one, but
> the price tag might be an issue.
>
> Thanks again for your comment and have a nice week-end!
>
> Marc-André Filion 
>
>
> -----Message d'origine-----
> De : Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx]
> Envoyé : Friday, October 14, 2011 1:17 PM
> À : Vinu Arumugham; Filion, Marc-Andre
> Cc : si-list@xxxxxxxxxxxxx
> Objet : Re: [SI-LIST] Re: 10G Differential routing trace width
>
> After you do a few designs making tradeoffs between loss, PCB thickness,
> routability and crosstalk you will discover that it is best to use traces
> of
> 4 or 5 mils and compensate for losses with better dielectric.  I use the 5
> mil trace all the way to 24 Gb/S.  As Steve points out, dielectric loss is
> a
> bigger player than skin effect loss at these data rates.  Secondly,
> routing
> the members of each pair to a "not closer than" rule to avoid unwanted
> interaction is also a good practice.
>
> And, as was pointed out, there are no rules of thumb for this class of
> engineering.  You gotta do the analysis!  Plenty of tools and plenty of
> data
> to make this possible.
>
>   One thing we still don't have a good handle on is the effect of surface
> roughness on loss, nor do we have a reliable way getting each fabricator
> to
> do it the same way!  Just a few little things that make each day
> interesting!!
>
> Lee Ritchey
>
> --------------------------------------------------
> From: "Vinu Arumugham" <vinu@xxxxxxxxx>
> Sent: Friday, October 14, 2011 9:18 AM
> To: "Filion, Marc-Andre" <marc-andre.filion@xxxxxxxxxxxxxx>
> Cc: <si-list@xxxxxxxxxxxxx>
> Subject: [SI-LIST] Re: 10G Differential routing trace width
>
>> It depends on what interconnect spec. you are trying to meet ...
>> 10-15 in. of 6 mil trace on FR4 would be way too much for XFI for
>> example but perfectly ok for KR.
>>
>> Thanks,
>> Vinu
>>
>> Filion, Marc-Andre wrote:
>>> Hi,
>>> I've got an easy Friday question. When it's time to design board with
>>> multi-gigabit (> 5Gb) differential signal, we always get lost into a
>>> discussion with CAD guys. We want more trace width to reduce loss and
>>> they want more real-estate to fit everything. In that case, increasing
>>> dielectric thickness is not an option because it will ruin the rest of
>>> the layer trace-2-trace clearance. In the end, we're stuck with a 6
>>> mils
>>> trace that will handle a 10G signal. We know, from previous design,
>>> that
>>> it's working, but I'm not sure if this is good practice. We have to go
>>> into 10 ~ 15 inch of routing with interconnect.
>>>
>>>
>>>
>>> Is there a rule of thumbs about trace width and signal speed?
>>>
>>> When Skin effect become a problematic issue?
>>>
>>>
>>>
>>> Many thanks,
>>>
>>>
>>>
>>> Marc-André Filion
>>>
>>>
>>>
>>>
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