Hi folks - Just a comment - The JSTD-003 committee had a committee member 
bring up a similar issue for discussion some time back. The driving 
parameters - SAC305 and ENIG pwb finish -  caused a black residue during 
soldering. I have seen it very random,  sporadically when doing some 
manual leadfree soldering on ENIG test vehicles and Gerard OBrien has 
observed it a couple of times too. We called the phenomena "black tar" 
which I suppose is going to not make folks happy but that is what it 
looked like. Some initial thoughts were that the black residue was a 
reaction product between the flux and the nickel plating but no one has 
been able to confirm that hypothesis.

Dave Hillman
Rockwell Collins
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Steve Gregory <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
06/09/2011 08:59 AM
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Steve Gregory <[log in to unmask]>


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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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