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

While looking into that surface roughness issue, particularly on inner
layers, I came across an article by one of our own:

Dr. Howard Johnson's article on copper surface roughness as it pertains
to high speed signals
http://www.sigcon.com/Pubs/edn/SurfaceRoughness.htm

And although Dr. Johnson doesn't mention this copper by name, I found
this 'dendritic' copper:

Olin Brass (http://www.olinbrass.com)=20
http://olinbrass.olin.com/xtf/Tech/CopperBond.cfm

I haven't seen studies on its benefits over the standard, reverse treat,
or double treated coppers available in the industry as they relate to
high frequency, but Dr. Johnson's article seemed to make intuitive
sense.

David, you mention some constituents involved in the production of
copper (e.g. brass, chromium, and silane), and although they may be
present to serve other purposes (release sheets, anti-corrosion, and
shelf life), in the end (in a PCB) I believe the copper to be
essentially pure with a oxide finish (on inner layers only) to give it
some tooth for the resin prepreg to 'grab' onto.  ..mike

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of David Greig
Sent: Tuesday, February 22, 2005 7:11 AM
To: wrobelc@xxxxxxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: si-list Digest V5 #82

Problem is that Ni is a ferromagnetic metal with permeability of about
100
(not sure if this is true for immersion Ni) and a conductivity about 4
times
Cu. Skin depth is going to be about 1/sqrt(ur*sigma) times that of
metals
with a ur=3D1 (Cu).
What little understanding of RF and microwave that I've got would
suggest
that most of the current is forced by the H field to the periphery of
any
inductive loop, in this case the Au and mostly Ni. If we take Cu, skin
depth
at 1GHz is about 2um and Ni is going to be about .5um. Most of the
current
is going to be in the Ni, and a much thinner layer of it than Cu - trace
resistance is gonna be about 4/(.5/2) or about 16 times more than Cu,
growing by the square root of frequency relative to 1gig.


Anyone got any ideas on what the rough side of ED Cu does over
frequency?
Given it's nodulated, plated with brass and chromium and covered with
stuff
like silane, it's probably best the H fields keep the current well away
from
it!


Best Regards
=20
David Greig
______________________________
GigaDyne Ltd
Buchan House
Carnegie Campus
Dunfermline KY11 8PL
United Kingdom
t: +44 (0)1383 624 975
______________________________

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Clayton Wrobel
Sent: 22 February 2005 13:21
To: si-list@xxxxxxxxxxxxx
Subject: [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. =3D20

    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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