Re: [SI-LIST] : skin effect

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From: Ray Anderson (raymonda@ha1mpk-mail.eng.sun.com)
Date: Thu Aug 31 2000 - 10:31:33 PDT


Muhammad-

        I'll keep this very intuitive and non-mathematical because I don't
feel like typing equations this morning.

Consider that skin effect causes an effective increase in high-frequency
resistance because the high-frequency current tends to flow mainly on the
surface (or skin) of the conductor.

        At high frequencies the skin depth is very thin. For example at 1GHZ
it is about .002 mm deep. Half ounce copper is about .7 mils thick (.18 mm).
So the skin effect removes .002 mm of effective thickness from each side of
the conductor .18mm - ( 2 x .002mm) = .176 mm . So doubling the copper
thickness to 1 ounce material (1.4 mil or .36 mm) won't do you any good as a
means to reduce the skin loss as the current is still flowing predominantly
in the outer .002 mm of the conductor no mater how thick the metal is.

        However, by making the conductor wider you can reduce the skin effect
because you increase the surface area of the conductor which provides more
parallel "squares" of material in the conductor which reduces the effective
resistance.

-Ray

> 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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