The main thing to check with your fab house is the phosphor concentration
in their Nickel Plating Bath. Maybe take a sample and have it independantly
analysed if you're in any doubt. If it's higher than about 10%, this is
probably the cause of your Black Pad (it should be between 6 and 8% for
good results). Also, make sure they don't allow the boards to dry out
between the Nickel plating process and the Gold Plating process, or the
Nickel will oxidise and also cause problems.

Peter Duncan



                    Earl Moon
                    <[log in to unmask]        To:     [log in to unmask]
                    M.COM>               cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by:             Aero/ST Group)
                    TechNet              Subject:     Re: [TN] ENIG-Black Pad
                    <[log in to unmask]
                    ORG>


                    11/15/01
                    02:28 PM
                    Please
                    respond to
                    "TechNet
                    E-Mail
                    Forum."






Get back to your board supplier as soon as possible and discuss. I haven't
seen, or even heard of this problem in over six months now. I am in touch
with many ENIG users - as designers, assemblers, and test folks using
mostly
the big board fab houses though some protos are made in smaller shops.

I hope the problems is lessening because board shops are doing a better job
with better plating/coating chemistries and processes. Much has been
written
on this problem on this forum, so look in the archives.

Black pad is exactly as you describe and opens are easily found during test
but that's very unfortunate as then it's way too late. As received, you
cannot tell the problem exists.

Visually, upon device removal, non-wetted pads appear black where
non-wetting is observed often with solder "bumps or ridges" where wetting
did occur.
There is no possibility of rendering the black surfaces solderable. You
can't scrape it off and no matter how many times you try, you cannot solder
to it though I did once have success taking the boards back to the supplier
and have them HASL coated after stripping off the surface coating.

Wish you the very best in your unfortunate situation,

MoonMan

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