[SI-LIST] Re: Skin Effect, Au, and Cu

From: <Aubrey_Sparkman@xxxxxxxx>
To: <richard.moffat@xxxxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
Date: Mon, 21 Feb 2005 14:33:01 -0600
Soldermask changes the impedance (especially tightly coupled diff pair)
for lower frequencies too, just not as significant at low impedance
single ended traces.

It's less of a series (skin effect) phenomena; did you remember to
consider the impact of dielectric constant on impedance....

Aubrey Sparkman=20
Enterprise Engineering Signal Integrity Team
Dell, Inc.=20
Aubrey_Sparkman@xxxxxxxx=20
(512) 723-3592

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of richard moffat
Sent: Monday, February 21, 2005 2:23 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Skin Effect, Au, and Cu

Hi all

This discussion developed in another forum, so I thought I'd throw it
into this one to get some more comments.

For GHz signals, some people leave off the resist covering and have
traces gold-plated instead:  "At high enough frequencies (we do 18 GHZ
on rogers) the soldermask changes the impedance of the line."  I have a
bit of trouble with this reasoning, as (non-corroded) copper has less
resistivity than gold. =20

I would have thought that copper at skin effect freqs would be a better
conductor than gold.  Is the loss due to the soldermask coating greater
than the skin effect loss at very high frequencies?

Cheers,
Richard

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[SI-LIST] Re: Skin Effect, Au, and Cu

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