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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