Hi Marvin,

This is a fairly complex question.  We need more information about your process
to be able to give you any practical recommendations (pattern or panel plating,
DC or pulse/reverse, plating current density, are you trying to improve
through-hole or surface distribution, what is typical/highest aspect ratios you
are dealing with, what distribution do you get now, etc.).

Surface distribution (copper thickness at the center vs. the edges of the panel)
depends primarily on current density, geometrical dimensions of your plating
tank, anode/cathode placement/shielding, rack design and -- to a lesser degree
-- on the chemistry of the plating solution.  Surface/hole distribution (copper
thickness at the center of the hole vs. the land pad) is a function of current
density, surface/hole aspect ratio, circuitry layout (if pattern plated),
conductivity of the solution (a hole filled with electrolyte works as a
"resistor"), plating chemistry, conductivity of the metallization layer (if not
electroless copper) among other things (mass transfer is not one of them, by the
way, unless you are trying to plate at a fairly high current density).  In
general, the biggest factor by far (in DC plating) is current density -- the
lower the better -- depending on how much time can you afford to spend in
plating and, if your chemistry allows you to plate at low current density.
Maximizing the conductivity of your plating solution (high sulfuric/low copper)
should be a priority as well.  For surface distribution -- tank/rack design
modifications, proper anode/cathode placement, shielding etc. can yield notable
improvements.  Contact me off line if you wish to discuss it further.

Eric Yakobson
Alpha PC Fab




"marvin v. picardal" <[log in to unmask]> on 08/31/99 02:24:56 PM

To:   [log in to unmask]
cc:
Subject:  [TN] how to improve plating distribution




TECHnet'rs,
Greetings!!! PCB Geniuses

I want to gather suggestions regarding items to be considered to maintain even
distribution for copper plating. So far I have already evaluated the effect of
board spacing, organic chemical dosage control, tank design modification. But
the result shows only few developments.

Other related principles such as that of mass transfer would be of great help.

thank you.


Marvin
Chemical Engineer
PWB

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