We use plasma all the time for surface modification/cleaning prior to
parylene coating. As Inge stated, no reason to take the finish off, 300w
max. Usually only at 150w of power.
Lloyd E Duso
Plant Manager
(814) 535-3505
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Wednesday, February 06, 2013 10:11 AM
To: [log in to unmask]
Subject: Re: [TN] Silver Sulfide & Plasma
........Plasma will take the finish right off....????? Are you sure you
talk plasma cleaning and not reversed sputtering? THAT takes the finish,
because of very heavy ion bombardment (etching) in opposition to cleaning
(reaction) that use much less energy . I had trouble with the operators,
because they did not follow the instructions, but performed plasma operation
as they thought was best. Then it may happen that the finish goes. i have
heard about similar problem with other industries, they buy the machine,
install it, but don't send the operators on adequate courses.
And later tell the world that plasma cleaners are crap.
Inge
On 6 February 2013 14:53, Stadem, Richard D.
<[log in to unmask]>wrote:
> 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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