Ah yes, I should have asked which Humiseal product was being used. I have
been using 1B31 for years and have used two other Humiseal acrylics. Forgot
they do have different drying characteristics.
-----Original Message-----
From: Phillip Bavaro [mailto:[log in to unmask]]
Sent: Thursday, 27 October 2005 2:43 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] Urgent! Acrylic coating
Hi Ingemar,
Even though you already have lots of good clues to go check.....my guess is
that you are seeing excessive evaporation effects....
IB31 dries at room temp but I remember creating beautiful patterns in the
coatings (but that was many years ago....) and it had to do with the
evaporation rate.
Did anyone change or maybe remove the exhaust filter media in the drying
chamber?
Phil (really old school conformal coater....)
Ingemar Hernefjord <[log in to unmask]> wrote:
A whole trouble shooting list! Thanks Cris, wonderful! This proves again
the high standard of TN. I will read your words carefully, a lot to
consider..my,my. Can anyone send a typical 'webbing' pic to Steve? What
are the webs? Just topographic irregularities or some chemical disorder?
Inge
-----Ursprungligt meddelande-----
Från: Schaefer, Chris [mailto:[log in to unmask]]
Skickat: den 27 oktober 2005 17:58
Till: TechNet E-Mail Forum; Ingemar Hernefjord
Ämne: RE: [TN] Urgent! Acrylic coating
Hey Ingemar,
I agree with alot of what has been said and it is very good information,
but what I was curious about was the materials used. One of the
statements mentioned was whether the solvent base was considered a
"fast" or "slow" solvent - this makes a huge difference depending on the
application method utilized as well as the coating type. We are
currently using an inline 8 gun selection conveyorized spray system
spraying acrylic Humiseal 1B31-LOC with what I consider a "slow" solvent
applicator. In the past we have had issues with the mixture ratio's
(viscosity) in which not enough thinner was added to the mix and thus
causes the "webbing" defects to literally fill the booth within about
3-4 minutes. We also had an issue when an operator used IPA instead of
the thinner and this caused the booth to fill in about 20-30 seconds. So
you may want to look at and make sure you are using the correct thinner
additive and make sure there was not a mistake. There was also a
statement about pre-baking the CCA's prior to coating them - with my
experience if they are coated while the CCA's are still hot, then you
may see the defects mentioned and others.
I would just go through the entire process variables and make sure they
are in fact set correctly. Change out the chemistry, purge the coating
lines (if possible), check the temperature (69-73 should work just
fine), make sure the atomization is correctly set and that the air lines
are free from moisture, make sure the CCA's are actually clean prior to
spraying them (this is a very big deal and needs to be validated or it
will causes many problems), and last but not least as mentioned check
the coating container to ensure that it has not been exposed to the
environment for over 24 hours (as this will cause the base solvent to
evaporate and change viscosity). Oh and one last thing. Check the output
volume of the guns to ensure that they are within the set band. If you
have a low out level and a high atomization setting, this may cause you
problems as well because depending on the viscosity of the material will
produce a very thin and weby type appearance on the CCA's substrate.
There's my 2.5 cents
Good Luck
CAS
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ingemar Hernefjord
Sent: Thursday, October 27, 2005 9:32 AM
To: [log in to unmask]
Subject: [TN] Urgent! Acrylic coating
Hi all,
I got a call from our production. They stopped the board coating. All
boards get white and superthin veils, patterned like fractals or roses.
I'm at home because of illness, so I can't participate in their work
with the problem.
I asked them for how long they bake the board before spraying, and they
told me that no baking is made at all. Does sound wrong to me. My first
theory is humidity in some form. Humiseal, don't have the article number
just now.
Anyone who has a tip?
I'll get pics sooner, maybe I can resize them for Steve's gallery.
Thanks in advance
Ingemar Hernefjord
Ericsson Microwave Systems
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