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August 2001

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From:
Andrew Hoggan <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 3 Aug 2001 11:09:11 +0100
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Hi Bill,

looked at the pictures and re-read your description. Thought it was maybe
reside from the solder mask. Are you using LPISM? But I'd expect no solder
if there was mask residue present. Difficult without the boards in front of
me. You could try a quick SEM-EDX analysis look for organic residue in the
same areas on un-soldered boards. Of course that's only if residue looked to
be an issue.

If your OA flux worked then I doubt it'd be a residue issue, mask residue is
a pretty robust substance.

Best regards,

Andrew Hoggan
BBA Associates Ltd
www.bba-associates.ltd

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kasprzak, Bill (sys)
USX
Sent: 01 August 2001 13:35
To: [log in to unmask]
Subject: [TN] Process Problem vs Board Problem


Technetters'

I've recently run into a problem with Wavesoldering some circuit boards
where I am having problems getting topside solder joints. The process that
I'm running has the topside of the board at 195-200 F just prior to the
solder wave. My conveyor speed is 4.0 fpm. My fluxer is a spray fluxer. The
board is a .062 - 6 layer board that has an aluminum heat sink on it. I feel
that my process is set correctly.

The original process that previously used on these boards was very
successful when we used an OA water soluble flux. This process was on that I
qualified many years ago to  J-Std-001A for Class 3 assemblies.

On these circuit boards, I'm trying to use a No Clean Lo Activity level flux
that is water washable. Because I have new equipment for wavesoldering, I
was hoping to not have to do a re-qualification process for our level 3
assemblies. Because our new equipment has much better controls than our old
equipment I thought that it would be easy to solder these boards with an LO
active flux. Well, my initial pass has been a disaster so far. There are
three pictures that I'm looking for comments on. They are located on Steve's
Webpage at http://stevezeva.homestead.com. (A thousand thanks go out to
Steve Gregory for providing a site for posting the pictures.) Two of the
pictures, called Bare Pad and Bare Pad2 show a condition that I can describe
but I don't know if this condition has a name. In those pictures, there is a
heavier coat of solder on the pad, but it seems to form a concentric ring on
the pad.The extremities of the pads, both toward the outside and the inside,
show a tinned surface but it appears to be much thinner. To me, it seems
like these thin areas do not readily solder. It seems like this thin area is
barrier that can only be overcome with a very strong OA flux. This may
explain why I did not have a problem before. The other picture shows another
condition that I see in various places on the bare board where there are
protrusions on the inside of the PTH's. This appears to be trapped volitiles
that were being expulsed during the HASL process.

I'm trying to determine if I have a board problem or a process problem.

Is it unreasonable for me to think that this board can be soldered with a
no-clean (but water washable) LO activity level flux?

Any help or comments would be greatly appreciated.

Bill Kasprzak
Moog Inc., Electronic Assembly Engineering

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