RE: [SI-LIST] : skin effect

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From: Dunbar, Tony (tony_dunbar@mentorg.com)
Date: Thu Aug 31 2000 - 10:47:47 PDT


Muhammad,
 
Both of your viewpoints (i.e. yours and your bosses) each have merit. But I
think your boss's adds the fine detail correctness. This is because the
current will always try to find the path of least impedance. This path will
tend to be where the coupling is tightest to its return path, typically the
trace's reference plane (or the complementary net of a diff. pair). If we
are considering a trace over/under a reference plane, the higher frequency
current will 'hug' the edge of the trace closest to the plane rather than be
distributed uniformily around the total edge of the conductor.
 
Therefore, a wider trace will facilitate the distribution of current better
than a taller trace and tend to have a lower resistance per-unit-length.
It's a very fine argument, I believe, within the realms of practical board
trace design because your trace widths are driven by other factors to be a
defined size and you will not be increasing the width to account for skin
effect. Above 100MHz, skin depth of copper begins to drop below 0.25mil so
whether you use 1oz or 1/2oz will not make much difference in the high
frequency band unless you are conducting heavy currents.
 
Regards,
Tony

-----Original Message-----
From: Muhammad S. Sagarwala [mailto:msagarwa@san-jose.tt.slb.com]
Sent: Thursday, August 31, 2000 11:45 AM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : skin effect

Hello Si Gurus,
 
I just had an interesting discussion with my boss on "skin effect on pcb
traces".
I was of the opinion that increasing the trace thickness from 1/2 oz. to
1oz. would help reduce the
skin effect but according to him skin effect does not reduce significantly
with the increase in trace thickness.
He was of the opinion ( and also had some data to back him up) that skin
effect is more dependent on the
width of the trace.
 
I always thought that if one increases the overall perimeter of the pcb
trace - regardless of whether it is done by
increasing the width or increasing the thickness - the skin effect would
reduce. I would appreciate if somebody
could come up with a better explanation...
 
Muhammad
 
p.s.: when we talked about pcb traces we were talking about striplines in
particular...
 
 
 
 
 
Muhammad S. Sagarwala
Design Engineer
Schlumberger SABER
Ph. (408) 586 7065
Fax (408) 586 4668

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