wrote:-
>OK Technetters - Here's another one to think about.  If you run boards
>through the line and leave them in acid copper WITHOUT plating current, even
>for the full duration of a typical plating cycle, you may see some attack
>and/or what looks like pink ring formation.  Even the creation of a small
>"wedge".  
>
>Take another load of boards and run as you normally would, with current
>applied by ramp-up, going in hot or whatever, and you'll see pink ring within
>minutes.  Sort of leads you to believe that the oxide dissolution, while it
>is chemical, is markedly accelerated by electrolysis.

This reminds me of another phenomenon which I had when using electro-
cleaning which was a good way of cleaning the copper surface prior to
plating in the days when photo resist was not so easily devloped off.

The panel was made anodic in ortho-phosphoric acid. What I noticed with
multi-layers was an attraction of copper particles forming inside the
holes at the junction with the inner layer to the extent that the hole
was almost blocked. This did not occur with unconnected holes.

This would be the reverse effect of making the panel cathodic and seeing
an increased attack at the inner layer junction as described above.
There must be some sort of capacitance effect here but all the layers
were connected through the electroless copper and so there should not
have been any voltage difference. I would be grateful if someone could
explain this phenomenon as I never could rationalise it.
-- 
Paul Gould
[log in to unmask]
Isle of Wight,UK

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