Have they looked at the solderpot and analyzed the alloy - high copper
concentrations can effect intermetallic bonds - this coupled with a
surface tension created from poor micro-roughning may cause this. It
does seem that some residue, maybe from LPI develop is present.
I tried to simulate this in our HASL process and could not.
Jeffrey Bush
Director, Quality Assurance and Technical Support
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302-1890
Tel. 802.257.4571.21 Fax. 802.257.0011
[log in to unmask]
http://www.vtcircuits.com
-----Original Message-----
From: Marsico, James [mailto:[log in to unmask]]
Sent: Wednesday, July 21, 2004 7:34 AM
To: [log in to unmask]
Subject: Re: [TN] PWB SOLDERABILITY
No, no nickel...
Our PWB supplier claims that he was able to repeat the problem by
"slightly" oxidizing the copper. When they subjected bare copper boards
to an oven bake, completely oxidizing the copper, the results of the
HASL was non-wet areas. When the bake was reduced, minimal oxidation,
he claims that he got the same results as the production PWBs, where the
pads were covered with solder, but, when subjected to a tape test, the
solder peeled off.
Luckily, this problem is only found on one part number (out of six that
were ordered), all of which were HASLed on the same day. We are
returning all un-built boards and our supplier will strip the solder and
re-HASL. My BIG problem now is, how do I screen the built-up
assemblies? We built about 40 of these (quite expensive) assemblies and
we're assuming that about 20% are suspect. My first action is to do a
tape test on the completed assemblies (on un-used pads) to try and weed
out some of the problem boards. After that, I really don't know what to
do with the assemblies that passed the tape test.
Suggestions?
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]> 631-595-5879
-----Original Message-----
From: [log in to unmask] [SMTP:[log in to unmask]]
Sent: Wednesday, July 21, 2004 6:07 AM
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] PWB SOLDERABILITY
Never, any chance they might have been nickel plated before
HASL?
-----Original Message-----
From: Marsico, James [mailto:[log in to unmask]]
Sent: Tuesday, July 20, 2004 8:29 PM
To: [log in to unmask]
Subject: [TN] PWB SOLDERABILITY
Good Day Technet:
Here's an unusual situation. We recently got a lot of PWBs from
our
supplier who we've been using for years. The solder on the
boards
(HASL)
looks good, thick and shiny. A couple of weeks ago, after SMT
assembly with
a fairly aggressive water soluble solder paste, we noticed that
one of the
components (diode) had fallen off and was sitting on the
operator's bench.
The pads on the board where the component had fallen off showed
bare copper,
while the solder fillets remained on the component! Thinking
that this was
an unexplainable one-time occurrence, the component was soldered
back on and
the board went on its merry way. Well, a couple of days later,
boards from
the same lot were soldered and we noticed that some of unused
pads or test
pads were copper only, with no traces of solder. We then took
some bare
boards, all of which looked good, and ran them trough our reflow
and in-line
cleaning process (no flux or solder paste). Low and behold, on
about 20%
of the boards there were copper pads with no solder, and a few
pads where
the solder was partially peeling off the pads, exposing the
copper
underneath (with no traces of copper on the pealed solder).
After
discussions with our supplier, we both came to the conclusion
that some of
the boards must have been oxidized to such a degree that solder
coated the
pads but did not achieve a metallurgical bond. I would have
thought that
such a condition would result in a de-wet or non-wet condition,
but, as I
said earlier, the boards looked great!
Has anyone else ever come across this before?
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
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