In your message dated Monday 18, November 1996 you wrote :
> We find dull copper after tin stripping on few pads of both
> Double and Multi layer boards. Even after reprocessing thru'
> Tin stripper, we find the dullness on the same pads. These
> boards after solder masking, hot air level without any
> problem. However, when electroless nickel gold finish is done,
> we find less nickel thickness on these pads. We use nitric
> acid stripper and acid copper and tin plating. 
> 
> Can anyone throw some light on this problem?
> 
It seems unlikely to be the tin-lead stripper if the same pads are affected 
on every panel. Could the dullness on be coming from the copper plate due to 
current distribution effects? The area of copper in the hole will cause a drop 
in current density on the surface around the hole. This effect is greater on 
smaller diameter holes.

Low current density usually results in duller deposits and low cd areas are 
generally in the centre of the panel, but this will also depend on the vat 
configuration and the board design. Is there sufficient air and mechanical 
agitation to prevent local depletion in the copper plating solution?

There should be a good range over which bright depostits are obtained which your 
Hull Cell test will show. Check the panels at the copper plate stage and if 
okay, check them again after tin-lead stripping.

I can't comment on the reason for the electroless nickel problem.

Good luck 
-- 
Paul Gould
EMail [log in to unmask]

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