[SI-LIST] Re: si-list Digest V5 #82

If you  are using ENIG (electroless nickel immersion gold), which I 
beleive is the most common soft gold finish, it isn't the gold layer you 
have to worry about, but the nickel.
The gold is only 0.05 um in thickness, but the nickel is 3 um according 
to IPC 2221.  I read an article about a year ago, I don't have it handy, 
that explained the science of why it was so bad.  Perhaps somone here 
remembers it and has access to it.
Clayton Wrobel

    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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