Hi Phil, Steve and TechNet! Sometimes what we see isn't always what is
really there! I wouldn't feel to silly Steve - I also looked at your jpeg
file and it did appear to be dewetted. It also looked somewhat like an
oxide float (e.g. tin oxide floating on the pad surface - analogous to a
lake with a section of sheet ice floating on the surface). This oxide
floating issue is one reason that the JSTD-003 committee has put a new test
in the 003 revision - Test E "Surface Mount Process Simulation Test". The
003 specification has included a wave solder test for through hole printed
wiring boards (Test D) for many years and the committee consensus was that
surface mount boards should be tested in a surface mount process if
applicable. Stenciling a board and running through the reflow oven will be
a test method choice available once the 003A specification proposal is
issued (that should happen by January).
Dave Hillman
Rockwell Collins
[log in to unmask]
hi,
well, look at it this way. at least they know you are looking. my cynical
opinion is this: if they don't think you are looking, they'll send you
everything that comes off the end of their line.
on the other hand, i think a solderability test at receiving inspection
that consists of a test print and oven reflow is a terrific idea. you'll
need to get your supplier to agree that lot acceptance will be based on the
results of that test. they may not be too keen to do that.
phil
> seen the pictures, and rad the responses. A lot of good posts. At the
risk
> of being redundant, her's what I've run cross as root causes for this
sort
> of dewetting.
>
> 1. LPI Solder Mask residue. Either from incomplete developing, poor
rinsing
> and dried in place, or redeposit from a poorly ventilated cure oven.
Either
> case difficult to see with naked eye prior to HASL processing.
>
> 2. Oxidation of copper from LPI cure bake not properly removed by
preclean
> for HASL (microetch).
>
> 3. Poor flux wetting to surface. Boards not properly dried of rinse
waters
> after pre-clean and prior to application of flux at HASL. Trying to flux
wet
> panels doesn't work well. Or poor flow of flux through the flux rollers.
>
> Hope this helps
>
> Bob Dube
>
> ES&D
Hi Bob and Everybody!
Well, had a conference call about an hour ago with our fab vendor. Not
mentioning any names, and I'm not trying to trash anybody, but the call was
interesting.
There were a couple of people there from their side, and me, our quality
engineer, and purchasing manager on our side.
The conversation started by them stating that they didn't see a dewetting
problem (I sent them the same pictures you looked at). They said that the
reason the solder looked like that was because they use a vertical leveling
machine, and that's the nature of the HASL process. They stated that they
build boards for other customers and the boards all look like that and
they've never had a complaint from any of their customers about
solderability
problems.
I was kind of dumbfounded...me and our quality engineer kind of stared at
each other with a big question mark over our heads. What they were saying
was
180° out from the input I've gotten from everyone here. So then I asked;
"You
mean you disagree that those pictures don't show dewetting?" They replied;
"Yes, that appearance is normal...and besides you can't say there's a
problem
with dewetting until you do a test like running the board over a wave or
solder dipping it to see if there's really dewetting occuring." I replied;
"We have boards here from other vendors that have been HASL'ed, and they
don't appear like these boards do..."
So I told them that I would take a board and print it with solder paste and
run it through our reflow oven...that I wanted to test it that way because
that's the way it would be assembled.
I did, and the solder did cover the pads and adhere pretty much, however I
did notice on a few pads that the solder did not flow out to the very edges
of the pads.
So are the boards okay? Or was I "the boy who cried wolf" on this deal?
'preciate any comments...ya' live and learn.
-Steve Gregory-
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