Sean: It is not unusual for plating deposits to start building on older
plastic coated racks. After X number of cycles thru cleaners, microetches
etc the plastic surface becomes porous and absorbs conductive chemistries.
Any type of conductive material such as palladium or carbon will only make
it worse but are not necessary to make this happen. Small electroplated
sites begin to form that continue to build with each additional cycle.

These plated up areas can either be chemically or as you have done manually
stripped. Chemical stripping is typically much faster if you have a lot of
racks and it also strips out most of the material seated down into the
plastic coated surface. However you need to make sure your stripping
chemistry is compatible with the plating you are stripping, the type of
plastic coating you are using and the rack contact areas. There are both
proprietary and generic(nitric acid)products available. Don't forget you
will now generate an additional waste by-product.

Typically after a few years, depending on your usage and application, the
coated racks are stripped and recoated.



Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076


-----Original Message-----
From: Sean Clinton [mailto:[log in to unmask]]
Sent: Thursday, October 25, 2001 1:57 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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