Burned copper (plating too fast) will also cause a granular/nodular
appearance.  Typically you'll see burned copper at high current density
areas but you can burn the entire copper surface.  High current density
areas are areas toward the outside of the panel (which you probably won't be
able to ascertain), isolated traces, the inside edge of the plated through
hole.

At some point burned copper should be rejectable but I honestly don't know
how to quantify it.

Can/would  any of the other Technetters offer comments on this?



>From: George Milad <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
>To: [log in to unmask]
>Subject: Re: [TN] Plating nodules
>Date: Sat, 11 Dec 2004 10:08:18 EST
>
>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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