Just listened to a Lead Free presentation by one of our assembly materials
suppliers.  They tested different pastes on different board finishes using a
variety of different patterns, spacings, aperture sizes, etc,...
By far and away, ENIG was the best finish for performance, for wetting,
defects, voiding, ...
The guy making the presentation said that he felt a lot of the initial
concerns re ENIG - black pad being the biggest - have been resolved, and
that they are no longer a concern, that they have determined what the cause
of it is and eliminated it.  Anyone want to comment on that?  I'm not sure
if he is correct, or just out of the loop.
It was interesting as well:  ImmAg got a very bad rating from them in
performance, even though many on this forum really praise that finish.  It
exhibited dewetting (they printed solderpaste pads on an area with no
soldermask, and the solder did not stay and spread where it was printed, it
crept together with other pads into a big blob, like you might see a water
drop do) and the amount of voiding was impressive!!
About 4 years ago I joined this forum, and one of the reasons was because I
was looking for info on ENIG.  We had done a prototype run of a couple of
boards and they failed miserably.  They were never analyzed in depth, so it
wasn't figured out what exactly caused the failure.  It was the excuse we
needed to not choose this finish and some of the extra costs associated with
it.
However, with the Pbfree push now, I don't know if we should re-examine
whether to use the finish.  For products where we needed a flat finish, we
have gone to ImmSn, but we still use HASL wherever possible.

Genny

"Genius may have its limitations, but stupidity is not thus handicapped"
Elbert Hubbard

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