Dear Ms Polmanteer,
        When we were building PWBs at GE Fanuc, we occasionally experienced
the exact "pits" that you are describing.  The primary cause invariably was
supersaturation of the copper plating solution with air.  The air was
induced to the plating tank through the filtration system, and could be very
difficult to trace.  One thing that made troubleshooting difficult was that
it took about 24 hours for the air to come "out of solution"-----just
turning off your filters for "a little while" will not make this go away.
Try leaving your filtration off overnight, and do not turn it back on until
after you have plated a rack to look for pits the next morning (this assumes
that you are not using liquid sparging). You may find your problem gone.
        I must credit the Tech guys at DuPont with this advice as they were
the ones who pointed us in this direction initially.  They used to have a
tech paper on this. . . maybe it is still available.

Greg Anderson
Advanced Manufacturing Engineer
GE Fanuc Automation, N.A.
Charlottesville, VA
e-mail:  [log in to unmask]


        -----Original Message-----
        From:   Sharon Polmanteer [SMTP:[log in to unmask]]
        Sent:   Thursday, December 10, 1998 11:46 AM
        To:     [log in to unmask]
        Subject:

        To Richard Haynes

        Hi Richard,

        We have been having intermittent trouble with (what most people
call) pits
        in electrolytic Cu plating.  The location of these pits is always at
the
        resist sidewall, they are always perfectly round, as are caused by
bubbles.
        Popular opinion is that this has been caused by oxygen induction via
        filtration system.  All four of the copper tanks we have are
different in
        physical construction and to have all the tanks cavitating air at
one time
        seems an outside possibility to me.  However, we have asked for
vendor
        guidance in new filtration system setup.

        Your comment on cathode-hydrogen evolution and oxygen evolution
interested
        me and I have some questions:

        A vendor told me that there is no hydrogen evolution in acid copper
as it is
        100% efficient.  I don't know.

         What physical characteristics do annodes exhibit when polizaration
occurs?
        Is there extremely irregular surface?

        Can high chloride concentration also cause polizaration, i.e. 144
ppm?

        When I pull a sample in a glass flask and look at the amount of
bubbles
        present, is turbidity the condition I'm looking for or the
size/quantity of
        the bubbles present?  I don't know what amount of bubbles should
cause
        concern.  Sorry if these are dumb questions.

        Thanks very much
        Sharon

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