If it is very bad why not run it back through a local board shop through
acid etch and re-coat after all it is an immersion process.....
Just a thought.
John
John Burke
General Manager/COO
Zollner Electronics Inc
Plant Milpitas
575 Cottonwood Drive
Milpitas, CA 95035
Phone: + 1 408 434 5442
Fax: + 1 408 434 5401
Mobile: + 1 408 628 2433
E-mail: [log in to unmask]
Internet: www.zollner-electronics.com
From: Gerald Bogert <[log in to unmask]>
To: <[log in to unmask]>
Date: 02/07/2013 05:07 AM
Subject: Re: [TN] Silver Sulfide & Plasma
Sent by: TechNet <[log in to unmask]>
----- Original Message -----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Wednesday, February 06, 2013 08:53 AM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Silver Sulfide & Plasma
Hi, Rich
If you have mildly tarnished IAg-finished PWBs, I recommend you print
paste on part of one of the PWBs or a complete solder sample coupon and
send it through the reflow as a solderability test. They will usually
solder out to the edges of the pads just fine. You can then wick off any
solder and still use it as a production PWB.
Wayne is correct. Plasma will take the finish right off.
If there are solderability issues, go back to the PWB vendor. There are
processes where they can strip off the IAg finish and re-plate the IAg,
and I have done this two or three times with no issues. If the PWB
supplier does not have this capability, there are others who can do this
for you, even if they did not fabricate the PWBs in the first place.
Typically the PWB supplier outsources this type of plating, and they can
tell you who can re-plate it for you.
I have used IAg PWBs that sat around in a warehouse for 5 years in a
previous life, completely exposed to the elements, and had turned a darker
shade of pale, so to speak. But they soldered up with a better DPMO than
the ones less than 6 months old!
dean
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Tuesday, February 05, 2013 5:31 PM
To: [log in to unmask]
Subject: Re: [TN] Silver Sulfide & Plasma
Hi Rich-
Mildly oxidized ImAg usually solders fine, even if it doesn't look good.
So try a bit. If you really need to do something, then I don't think a
plasma will help. There is only a very tiny amount of silver on the
surface, so if you remove the ugly stuff, you'll most likely expose a
bunch of copper.
So IF anything is needed, then the common approach is to REDUCE the silver
oxides and sulfides back to elemental silver. This is done the same way
as advertised frequently on late night TV (only they use snake oil and do
voodoo dances):
Heat some water up to 70C and add 1TBS/quart of baking soda. Dissolve the
baking soda. Then take some new shiny aluminum foil and crumple it up,
then iron it back out. Put this in the hot water bath with the circuit
board. It doesn't have to actually make contact with the circuit board,
and you really don't need a whole lot of aluminum foil. Within about 2
minutes, the freshly exposed aluminum will pull the oxygen and sulfur away
from the silver and you will be back close to the original finish.
Rinse THOROUGHLY in DI water, then dry the board in an oven until it is
completely baked out.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard Kraszewski
Sent: Tuesday, February 05, 2013 5:54 PM
To: [log in to unmask]
Subject: [TN] Silver Sulfide & Plasma
Any of you ever have luck cleaning silver sulphide off of a PCB enough to
make it solderable with NC flux, by using plasma?
If so , can you please provide me with the gas mix you used?
Thanks
Rich Kraszewski
PLEXUS
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