Hi, Ken,
I believe ENIG (or any other plating) can be applied either before or after
soldermask, but normally it's applied before to save on plating solution
costs among other things.
Yes, the immersion gold process is aggressive, so be sure your fab house is
using an ENIG-compatible mask. This often involves using an alternative
hardener in the mask mix, and it's better if your pads are not solder mask
defined, as the plating tends to get underneath the edges.
Masking from one side only, the holes can be cleaned, but it depends to a
large extent on the diameter of the holes and the capability of your fab
house. 10 mils and above, I believe, are OK, but smaller than that, the
cleaning process may have trouble penetrating properly and cleaning out the
bottom of the holes. I suggest you leave the holes open at both ends unless
you absolutely have to mask one end.
Peter
Ken Patel
<[log in to unmask] To: [log in to unmask]
OM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: Aero/ST Group)
TechNet Subject: [TN] Fab Process question related to
<[log in to unmask] ENIG
ORG>
03/08/02
01:40 AM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
Ken Patel
At what stage the electroless nickel and immersion gold process is
applied, is it after the solder mask application or before? I believe
normally it is after the solder mask application but I want to verify
it. I have heard that chemistry involved is very nasty if left on the
board. If I plug or mask via holes from one side, I want to make sure
that there is no residue left of that nasty chemistry. Can it be cleaned
if mask from one end? Any comments?
re,
Ken Patel
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