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October 2001

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Subject:
From:
Hinners Hans M Civ WRALC/LUGE <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 26 Oct 2001 11:17:53 -0400
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Hey Sean,

Do these racks have a cover that seals the contacts off from the bath?  I've
seen impressive rack plating when the contact's cover got stuck open.
Electroless plating is designed to put copper on non-conductive surfaces.
If you are talking electrolytic plating (panel & pattern) then the racks are
completing the circuit somehow.

I'd hazard a guess that you'll eventually have to either replace, recoat or
just stop using these racks.  Once the plated metal is there it'll continue
to build up everytime you use them.  In the short term, you might try
peeling the plated metal off with a non-scratching scrapper or using a
strong etch bath between runs (well ventilated area a must).  And since that
metal isn't getting plated onto the boards it adds to your costs.  If this
just started happening you might notice your chemistry adds getting bigger.

When I first started in this biz ('98) we were still using ancient racks
with uncoated wing nuts.  Talk about extra plating - up, down and all
around.  After a week or so the nodules could cut through your gloves easy.
It can be a real pain if your hand slips when your scrapping it off.

Hans

Integrity First  -  Service Before Self  -  Excellence in All We Do
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Electronics Engineer
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
Special Operations Forces System Program Office (SOF - SPO)
Gunship Team
226 Cochran Street
Robins AFB GA 31098-1622

mailto:[log in to unmask]

Com: (478) 926 - 5224
Fax:   (478) 926 - 4911
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-----Original Message-----
From: Sean Clinton [mailto:[log in to unmask]]
Sent: Thursday, October 25, 2001 4:57 PM
To: [log in to unmask]
Subject: [TN] Racks plating up


Hi All,

I have a slight problem that I want to avoid turning into a major costly
issue.  I have a few plating racks that are starting to be overrun with
wild plating ( copper and tin) up the rack away from the contacts in areas
that are not supposed to be plating.  There are even areas of isolated
plated metal surrounded by plastic.  Upon inspection, I was able to peel
off the plated tin and copper and noticed several layers.  I think this is
most likely due to multiple plating cycles.

The racks are solid copper core with a plastic shrouding.  The manufacturer
claims that "no rack stripping" is needed.  In the universe where I am
from, most plastics aren't conductive and don't plate.  I understand that
once initiated, the plating will propagate in the path of least resistance,
but what is causing it?

My suspicions include poor rinsing of the racks (conductive salts
remaining?) after a plating cycle or conductive carbon (from our Shadow
process) getting into scratches in the plastic shrouds and eventually
arcing causing this plating, but I haven't been able to confirm or disprove
either theory yet.  It's not affecting quality, but I don't want to wait
until it does.  Is there some preventative measure to eliminate the problem
that anyone has tried?

Thanks,
Sean Clinton

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