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Sat, 11 Dec 2004 10:08:18 EST |
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Nodules are protrusions over the plated surface. They are usually small in
nature and maybe conical, round or needle like.
There are some known causes for nodulation:
The first and foremost is the introduction of “particles into the bath”
that actually land on the plating surface. They offset the uniformity of crystal
growth and create surface imperfections. One example is a torn anode bag
that lets loose copper oxide fines into the bath, this gives rise to a sand
paper effect. Another is the introduction of fine carbon particulates after
C-Treat. The nodules formed here would have carbon in their core.
Second, is surface irregularities coming to the plating line. These could
come from the deburr operation after drill and or from surface preparation at
dry film lamination. Shadow/electroless residues on the surface could
contribute to this problem
Third, “Unusual Crystal growth” is the other cause. If the source of
nodulation is uncontrolled crystal growth, the answer will be found in manipulating
the additive package.
During deposition cystal growth is controlled by the additive package. The
additive is compromised of three components:
Brightener
Carrier
Leveller
The carrier function is to create suppression and that is make it harder to
plate, when this happens the plating is forced to get organized into a
crystal lattice and creates good adherent plating. The cost of suppression is
increased plating voltage. The more suppression the better the surface and thru
hole copper thickness distribution.
The leveler serves a somewhat similar function to the carrier, it further
suppresses plating in the higher current density areas allowing the lower
current density areas to catch up.
The brightener is the ultimate grain refiner. Without the brightener the
plating would be dull and any imperfections would be pronounced. The brightener
controls the crystal formation thru grain refinement and hence the brightening
effect.
Nodule Solutions:
If the source is extraneous material then the obvious answer is to prevent
the material from coming to the tank and if it does then to have way to
quickly remove it (adequate filtration). Air could be a source, carbon from
C-Treat could be another, as well as sludge from the anode bags. The insoluble
anode would eliminate anode sludge from the picture.
If the nodules are a result of surface imperfections, these need to be
identified and eliminated.
If the nodules belong to the third type then the correction will be thru the
upgrading of the chemical additive system and its control.
Best regards
George Milad
[log in to unmask]
National Accounts Manager for Technology
Uyemura International Corporation
Technical Center
240 Town LIne Rd
Southington CT 06489
(516) 901 3874 (mobile)
(860) 793-4011 (office)
(860) 793-4020 (fax)
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