Russ,

I can give some general parameters on your electroless bath, but you should
contact your supplier very soon.

Your bath is "sanding" out onto the board.  Causes could be at least two --

1 There is particulate or foreign material in the bath from some other
source.  This is coming in on the board, in the room atmosphere, etc.  Do you filter
the bath through a bag at an overflow?  This is a good practice to be sure
whatever the particulate does not extend the surface available for plating, and
blow the bath.  For instance, these "sandy nodules" may now be accumulating on
the bottom of the plating tank, and you are consuming a lot of extra
chemistry.  You can check to see if hydrogen bubbles are coming up from the bottom
when there is no rack in the bath.

2. Some part of the additive chemistry from your supplier is coming out of
solution.  You have addressed chelator. However, there are other ingredients in
the bath -- stabilizers, possibly grain refiners, etc.  This may be what you
see.  20 years ago, a phenomenon known as "chicken fat" was observed in
electroless plating.

3. It is doubtful, but possible that your bath has built up to the point that
the formates formed by the reaction of caustic with formaldehyde are past the
solubility limit.  It is possible to formulate electroless so that specific
gravity builds up with time.  However, most baths today are supplied diluted
enough that this should not happen.  Old guidelines were to watch out above a
gravity of 1.14 or 1.15 in certain cases.  Check you specific gravity.

How long since you dumped the whole bath and built a new one?  I speculate
that you may be reaching instability, and the bath may plate itself out in any
case.  Your tank bottom may be building up with copper and this is adding to
your foaming.  How many square feet should have been plated with the chemistry
you added in the last couple days?  Much more than actually went through the
bath?

Contact me offline if you want more specific information.

Denny Fritz
MacDermid

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