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

Hi Mike,

The brass, etc, is pretty common on the ED side, e.g.
<http://www.gould.com/downloads/cf.pdf>
I could understand why this is functional on single and double sided boards,
but unless fabricators do similar on the drum side (outer) of cores in
multilayers then there seems little point - although I can guess where
de-lamination will start from!
Bit annoying when most of the stuff I do is 12l+, GHz+ and I could do with
nice flat copper surfaces without paying thru the nose for rolled foil.

I'm actually wandering on the figure of 16x resistivity for nickel @ 1G,
still trying to picture the quassi TEM at 1G and the current distribution in
the track centre. Must try it thru the simulator next time, kinda moved away
from ENIG long before having the cash for field solvers. Still, seems
logical though, 4 times the resistivity and 1/4 of the depth. Anyone got
some measurements over frequency?

Best Regards
 
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 msharpes@xxxxxxxxxx
Sent: 22 February 2005 15:28
To: david@xxxxxxxxxxxxxx; wrobelc@xxxxxxxxxxxxxxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: [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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