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

  • From: Dave Instone <dave.instone@xxxxxxxxxx>
  • To: richard.moffat@xxxxxxxxxxxxxxxxxxx
  • Date: Tue, 22 Feb 2005 08:43:51 +0000

Hi richard,
See below
Dave

richard moffat wrote:

>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.  
>
>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?
>
>  
>
Just a thought, but if the traces are running over a plane then I 
suspect that most of the current will be flowing on the underside of the 
conductor and having gold on the top will have little effect other than 
to stop corrosion, and make the board look pretty <g>

>Cheers,
>Richard
>
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