>From: "richard moffat" <richard.moffat@xxxxxxxxxxxxxxxxxxx> >Subject: [SI-LIST] Skin Effect, Au, and Cu >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. I might be totally off here...(!?) But the statement seems rather straight-forward: The soldermask is a dielectric differing from air, hence it will change impedance of the lines. Actually 18GHz should not be necessary to see the effect. >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? I would think the purpose of the gold plating is primary anticorrosion. And in opposition to soldermask the gold should not affect the microstrip being a conductor (and very thin). Others have addressed the losses - which is a more complex matter... Cheers, Anders =) ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu