Ken, repeated from old mails:
--------------------------------------------------------------------
I was myself looking for a non-magnetic finish once, and if I remember
right, there is a difference between EN and EN. The acidous electroless
nickel is not ferromagnetic, while alcaline electroless nickel is
somewhat ferromagnetic.
Borohydride electroless Nickel-Boron is probably non-magnetic too.
However, you should contact your plating chemist to verify, it was many
years since I mixed with this. (In earlier days, we had our own
chemists, many of them had piles of knowhow, but then came the
economist's era, and the chemists were kicked out)
Inge
-----------------------------------------------------------------
Now, Paymon's case was not a RF unit, but sort of a magnetic one, but as
many are interested in microwave issues I noted some matters years ago,
one connected to flux, the other to barrier layers. Sandia Labs had
something called 'Low Residue Soldering Task Force'. Dr Laura Turbini
and her group found a clear connection between the solder residues and
increased RF loss.
>From her report: 'It has been shown that polyglycols and hydrobromic
acid (constituents in some fluxes)diffuses into epoxy during the HASL
process. Under the humid conditions of this test, these processing
chemicals may change the dielectric properties of the test board, which
affect the RF signal integrity.' 451
After that report and some others, we are more motivated to keep
critical RF boards as clean as possible. Normally, flux residues are not
an issue, but some regions of a circuit can be very sensitive to losses.
The other object is rare. I'll send two pictures to Steve's Wax Cabinet.
These show how NiCr leaked out from the edges of the hot RF line and
deposited on the substrate. Caused severe changes in the circuit's RF
properties. We have seen it just a couple of times. No explanation found
how this works. Mystery among many other RF mysteries. The only thing we
could verify was that the 'bleeding' NiCr coincided with the electrical
field.
Inge
-----------------------------------------------------------------------
I can send Laura's report offline, if you want it. Or you can as Bev,
because Laura works for him.
Inge
---------------------------------------------------------------------
Ken, are you sure you can't use electroless nickel? Have you calculated
and simulated the nickel resistivity vs frequency, vs conductor length,
vs conductor geometry, simulated the electromagnetic wave for the whole
circuitry, calculated if you can accept the loss, pulse delay etc. We
use to spend hours, days, weeks with the various RF design programs
before we decide such changes as you refer to. One can't just say
'electroless nickel is magnetic, so we can't use it'. It's like saying '
air is contaminated, I stop breathing air'.
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Brooks,Bill
Skickat: den 21 juni 2007 18:10
Till: [log in to unmask]
Ämne: Re: [TN] PCB Finish
http://en.wikipedia.org/wiki/Nickel
Looks like Nickel is magnetic. They explain why the US coin we call
Nickel
is non-magnetic because it is mostly copper.
I know that in Microwave circuits nickel is very 'lossy' and an
undesirable
finish component for that reason...
Maybe someone with some metallurgy background can elaborate on the alloy
that you end up with when applying ENIG to the circuits on a board.
Bill
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Thursday, June 21, 2007 8:39 AM
To: [log in to unmask]
Subject: Re: [TN] PCB Finish
I thought the EN in ENIG stood for electroless nickel. Is electroless
nickel
non-magnetic?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wood, Kenneth
Sent: Thursday, June 21, 2007 9:46 AM
To: [log in to unmask]
Subject: [TN] PCB Finish
Hey all,
Question:
I design PCB's for MRI use so Nickel is no good because it is magnetic.
Is there a standard finish I can use that does not whisker like tin, has
no
nickel like ENIG and can be made by anyone (most at least).
What about Silver?
Thanks
Ken
__________________________________________
Kenneth Wood
Senior PCB Designer
Invivo Corp.
12601 Research Parkway
Orlando, FL 32826
Phone: 407-275-3220 ext. 179
Mobile: 407-340-2668
Fax: 321-239-1910
Email: <mailto:[log in to unmask]> [log in to unmask]
Internet: <http://www.invivocorp.com/> http://www.invivocorp.com
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