Hi,
Wow, I did not see a lot of "Pad" on that black pad! :-) The black seems
to be on the via wall?
Something about those picture really bugs me. Something seems really wrong
here and I think it is a combination of the PCB Design (specifically vias)
along with the PCB fab process.
What I see is no solder mask relief around the holes. If vias were tented at
some point there could have been liquid entrapment followed by who know what
type of reaction with wall metal.
Now I am NOT a PCB fab guy but I recall at some point in the SMOBC process
the copper is oxidized to black (I think) to enhance mask adhesion. Later
that oxide is removed for finishing metal coating. I could have that wrong,
I am sure someone can correct me.
If a via became tented would via oxide removal fail with final via walls
remaining in a oxide coated state? I recall the solder mask is the defining
resist to the black oxide removal.
Just ideas. Again I am no PCB fab guy.
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, June 09, 2011 9:59 AM
To: [log in to unmask]
Subject: Re: [TN] Black Pad?
Hi Gary,
I got your pictures this morning, and have them posted now:
http://stevezeva.homestead.com/Joint_1.JPG
http://stevezeva.homestead.com/Joint_2.JPG
http://stevezeva.homestead.com/via.JPG
Although the pictures show some non-wetting happening, it's difficult to see
what exactly is going on.
You say that the component side seems fine, it's just when you're trying to
wave solder is when you see the problem. Maybe you have thin gold, and when
the boards were fresh, the SMT was able to solder fine. But then after the
boards went through reflow, the underlying nickel oxidized so badly that
solder wasn't able to wet?
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gary Robinson
Sent: Wednesday, June 08, 2011 4:46 PM
To: [log in to unmask]
Subject: [TN] Black Pad?
We have noticed a problem only on ENIG boards in our WAVE process that looks
similar to Black Pad but do not know how to identify or where to begin to
find a resolution to the problem. We were hoping an expert may have
experience in seeing this problem. Here are some facts - 1. Black residue
is on the vias and thts on the solder side. Please see the attached images.
2. Component Side SMT Parts do not exhibit the same problems.
3. Boards are processed PbFree - SAC305, Pacific 2009m No Clean Water Based
flux 4. THTs will not wet after residues appear (for touch up process) 5.
Blowholes appear to accompany the defect but are not always present.
Thanks for your help in advance.
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