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June 1999

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Subject:
From:
Dennis Fritz <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 5 Jun 1999 00:08:36 EDT
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In a message dated 99-06-04 18:09:12 EDT, [log in to unmask] writes:

<< I do not know why the Macdermid
 9241 acid copper plating bath needs carbon treatment after a certain
 amp-hrs. of plating? >>


1. The brightners and grain refiners in acid coppers are organic molecules.
There is a continuous breakdown of these additives as electrical current
passes through them - more than the drag out of copper plating solution can
remove with today's pollution controls.  So, the "Total Organic Carbon"
builds in the plating bath.  At some point, the organics start to interfer
with the copper grain structure in the deposits.  The tensile and elongation
properties fall off and you will get corner cracks in solder shock.  Carbon
treatment removes (hopefully) all these organics, so that you can start over
with a new brightner add, just like on original make-up.

2. The plating resist you are using and the cleaner solution at the start of
the pattern plate line are both  organics.   These are other sources of
organic molecules, besides the breakdown products from the plating bath
brightner.   They also are removed (hopefully) in carbon treatment.

You can control an acid copper plating bath by running Hull cells to
determine brightner effectiveness -or the effect of the organic impurites,
run a total organic carbon frequently to see how much organic is building up,
run some sort of chromatograph (ionic, liquid, etc) to see what compound is
building up, and run frequent physical property samples of your copper plate.


OR, you can use the guidelines we have established based on shop experience
around the world, and carbon treat after a specified number of amp hours per
gallon of plating bath solution to be safe.   Unless you have access to a lot
of analytical equipment, better use the amp hour recommendation.

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