In an earlier post, I had suggested several factors influencing surface:hole
plating and surface to surface distribution. One other explanation with
respect to surface distribution is looking at the limitations of mass
transport. We have a great deal of documentation showing that non uniform
solution movement across a panel (like dead spots where there is little or
no air due to a variety of reasons) leads to surface distribution issues. If
mass transport limitations do exist, it is possible that one could cause
uneven copper ion distribution across the diffusion layer. This non
uniformity in solution movement leads to over plating in some areas on the
panel. This is why it is suggested to have uniform mass transport. This does
not the agitation of the solution has to "blow the chemisty" out of the
tank. The agitation system needs to provide a uniform field of flow at the
work surface. In other words, we want to cut down the thickness of the
cathode diffusion layer uniformly.

With respect to rack design, a rack should be designed with first knowing
how many amps the rack will be required to carry. If you have a very
complicated design, you may want to consider a picture frame type rack with
many contact points for the work piece. Cross sectional area of the rack is
critical as well.
Good luck,
Mike Carano

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