Hi Dennis,

I don´t think that copper is in this game. It seems that this is caused by
the Ni/Au process. 
Yes, these are pads for a QFP with 20mil pitch and I took the pictures from
the worst sample to be found. So not all of them show this symptom just a
couple of boards.
My concern is could this be regarded as only cosmetical nature or something
to worry about? There´s nothing else to notice and solderability seems OK.
We would go the way with cross section only if there were a suspected danger
with this phenomenom due to our tight timeschedule.
If I knew that there were any danger with this I would suggest further
analysis but without funded arguements my boss will rip my head of for
blasting the schedule (we already are weeks after schedule with this job).

Wolfgang



-----Ursprüngliche Nachricht-----
Von: Dennis Fritz [mailto:[log in to unmask]]
Gesendet am: Montag, 27. August 2001 17:17
An: [log in to unmask]
Betreff: Re: [TN] phenomenon with Ni/Au plating

A cross section of the "pimples" should help isolate the cause.

If there is copper in the pimple - the problem goes all the way back to
board
fab - most likely strip and etch.  These would have been tight geometries,
so
incomplete stripping of image film, and resulting marginal etching would
leave these copper bumps.  They are now covered with nickel.

If there is no copper in the bumps, the nickel plating is implicated.  It
would help to know if it is electroplate or electroless nickel.  I suspect
electroless - as the pads seem to be for a peripheral lead device.  Thus
they
would have been nickel plated after etching of circuits. Over activation, or
dried on activator from an interrupted process sequence might give this
pattern.  But, I would expect even more extraneous plate - even on top of
the
mask dams, perhaps.  On the chance they were electroplated at the start of
the fab cycle, "burning" is the creation of electroplated nodules when the
electroplate current density is too high.

Do you know the fabrication sequence? Can you get a cross section of a
"pimple"?

Denny Fritz
MacDermid

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