FreeLists / si-list / [SI-LIST] Re: Thick vs. thin diff. pairs

[Ravinder.Ajmani@xxxxxxxxxxxxxx]

Mark,
Dr. Eric Bogatin had covered this subject in his monthly column "No Myths 
Allowed" in the July 2006 issue of Printed Circuit Design & Manufacture. 
The trace width selection is a compromise between higher dielectric losses 
for wide traces and higher conductor loss for narrow traces.  His 
conclusion: 7 mils is the optimum trace width for GHz interconnects on 
FR4.

Regards, Ravinder
Server PCB Development
Hitachi Global Storage Technologies


Email: Ravinder.Ajmani@xxxxxxxxxxxxxx



"Mark Burford" <Mark_Burford@xxxxxxxxxxx> 
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[SI-LIST] Thick vs. thin diff. pairs






Dear all, 
I would like to ask opinions, on the merits and disadvantages of using
wide or narrow microstrip lines.

From where I am sitting it looks like narrow microstrip diff. pairs have
it won hands down.

 

Thick lines:

More area...which gives more dielectric loss as dielectric loss over
takes skin effect losses at higher frequencies.

More S11 because any corner on the line will give a greater area and
more capacitance.

Thicker substrates to keep the impedance at the right value.

As thicker microstrip lines go round a bend, the inter-pair skew will be
more than for two narrow lines.

There is also the possibility of increased EMI from thicker substrates
(been reading antenna design books).

 

So please someone tell me why should we use thicker lines? And also
please could someone tell me the trip ups of HDI (high density
interconnect) such as how small can one realistically go with back plane
and inter-chip routing?

 

Thanks

Mark

 

 

 


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