[SI-LIST] Re: Trace width selection for high speed serial links

There are a couple of potential problems.  The first is space in all 
axes.  10 or 12 mil wide 50 Ohm lines will require pretty thick 
dielectric, and commensurately wide spacing to other aggressor traces to 
hold cross-talk to a given budgetary limit and that is not just on your 
SerDes lines but on your single-ended busses.  The thicker dielectric is 
going to push your power cavities further from the PCB surface, 
aggravating inductance to both ICs and bypass caps.  Another problem is 
that with that thick dielectric and wide spacing you could potentially 
see more timing skew from laminate weave, and other anisotropic issues 
with the dielectric such as varying moisture content and such.  
Typically above 500MHz to 1GHz dielectric losses dominate over skin.  8 
mils is about the widest that I see used.

Steve.

jhasson@xxxxxxxxxxxxxxxxxxx wrote:
> Hi,
> It is often mentionned in guidelines for routing high speed differential 
> serial links to have a trace width between 4 and 8 mils to reduce skin 
> effect losses. What would be the drawback of having even larger traces 
> like 10 or 12 mils if any ? The setup would be to use loose coupling and 
> the board density is not the main concern.
>
> Best regards,
>
> JF Hasson
>
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