Steve: I've responded to your questions and added some additional comments
in the text below.
Conveyor speed is typically 5.5 - 6.5 ft/min, chipwave 650 -750RPM rotary
250RPM , Lambda 620 - 700, topside board preheat 190 F.
We are using standard atmosphere, no nitrogen. Our Lambda wave is as smooth
as glass, your pump or nozzle may not be seated right or it may not be as
clean as you think.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, October 10, 2002 12:00 PM
To: [log in to unmask]; [log in to unmask]
Subject: Re: [TN] Dross particles sticking to soldermask...
Mike,
I appreciate your help on this, my answers to your questions are below in
parentheses...
Steve: We also run an Electrovert Electra. We use Alpha's 871-25 OA flux,
similar to your 2331 which we have also used, applied by foam fluxing.
Looking at your photos it's hard to tell but the "Dross Particles" appear
more like solder webbing than dross and the "More Dross" does look like
dross. I'm discounting a problem with the soldermask cure or board design
because
you say it's happening with all your boards. However you may want to verify
soldermask cure as a sanity check.
(you're right Mike, I did think about it at first, but I know that's not the
issue)
1. My first guess is that you are drying out the flux on the board. The flux
no longer can act as a lubricant/thermal insulator and the solder and dross
stick to the board surface. Obviously insufficient flux deposition,
excessive preheat, slow conveyor speed can all contribute. Is it
re-occurring in a given band or area where there may be lack of flux or a
hot spot in the preheaters?
(The flux does kinda' look dry, so I've lowered the preheat, and I still am
seeing the dross. It's random too, not in the same place on the boards. I'm
getting good coverage, I see flux coming up on the topside around the
fillets for the PTH stuff) Have you cross checked sp.gr. on the flux? Even
though there's and automatic controller on it we have seen some problems in
consistency i.e. excess thinner.
Also we are running a foam fluxer with 25% solids in the flux. Your spray
fluxer may need adjusting to deliver a heavier coating and you may be using
a lower solids flux which can dry out faster.
If item 1 is not the case consider the following:
2. Are you running the chipwave? This can be a large generator of dross. We
clean both the chip and Lambda wave pots of dross every two hours.
(Yes I am, got SMT on the bottomside...and we see the problem even when we
start off with a clean pot)
3. Is the overflow on the Lambda wave set correctly? If not you will not get
the proper overflow and dross will build in the wave.
(We're not seeing that at all, the lambda is not sitting static by any
means)
The overflow on the Lambda wave should be just be barely moving or stopped
with no product going across it. With a moderate overflow when running
product. You may have too much overflow generating excessive dross.
4. How often do you remove and clean the chipwave and Lambda nozzles? We
remove and clean every 80 hrs of operation. These have a tendency to build
up dross which comes up thru the wave.
(We are doing that, because it so simple to take out....)
Check to see that the wave nozzles and dross plates are seated properly
especially the Lambda.
5. How often do you teardown the entire solderpot and pull everything out
for a complete cleaning? We do a complete teardown every 1000 hrs. You would
be amazed at how much dross and residue is built up inside the pot and it's
internal components.
(We've only had the machine a month now, so we haven't run it that much yet)
Mike, would you mind sharing what your typical belt speed, preheat settings,
and pump RPM setting are?
One other question, this machine was set up with CoN2tour wave, but we're
not using nitrogen, we're not using compressed air either. Do you think that
may have something to do with things? The Lambda wave doesn't have a smooth
appearance except at very low RPM's...is that normal?
Thanks Mike!!
-Steve Gregory-
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