I once read that one of the possible causes of Black Pad was an electrical
imbalance in the plating baths, though that hypothesis was pooh-poohed by
many, because the plating processes are electroless. There are different
metals involved, though, and it's quite possible that some kind of battery
effect is created. If these effects aren't balanced, either in the design
or in the plating process, and it is a cause of Black Pad .....

The question is then, how does one determine if a design is appropriate for
ENIG finishing or not? Or another question is, how to tailor the plating
process for particular design features. It would be interesting to know if
the Fab House who passed this story on to you, Kathy, knows if the black
pad occured in the same area(s) of the boards each time or more randomly.
Also if the board design had anything apparently unusual about it.

A nice thesis for some PhD student!

Peter




                    Kathy Kuhlow
                    <Kathy@BTW-IN        To:     [log in to unmask]
                    C.COM>               cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by:             Aero/ST Group)
                    TechNet              Subject:     Re: [TN] ENIG black pad issues
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                    02/23/02
                    03:03 AM
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                    Kathy Kuhlow






I had spoken to a PCB supplier FAE a couple of weeks back and he was
mentioning that awhile ago he knew of a situation where a PCB had a problem
with black pad and the customer thought it was poor supplier process
control.  But when the product was moved to a PCB house that had been doing
this finish and had never had black pad before tried to build these same
PCB's now had a black pad problem.  If this is the case then couldn't black
pad be tried back to a design and process mismatch?  Anyone else know of
any further such stories?  Is this a possibility?

Kathy
(See attached file: TEXT.htm)



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