We heat the flux with a convection nozzle for rework and do not remove it.
NR205, in reasonable quantities, will actually disappears.
We also have an oven recipe that takes the surface of the board to 165 and
holds it there for 90 seconds. Have to be careful with this method though
some through hole parts don't like it.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Tuesday, May 22, 2007 6:17 PM
To: [log in to unmask]
Subject: Re: [TN] Flux residue, burnt flux
Well, no-clean burnt flux is definitely fully heated, and should be inert...
I don't know much about burnt flux, sorry.
For no-clean flux, internally, we say that all additional flux applied for a
hand-soldering operation must be cleaned. Un-heated no-clean residues can,
like other flux types, still be corrosive and conductive, a definite
reliability concern for any product.
The definition of "flux" is "a substance that aids, induces, or otherwise
actively participates in ... flowing". When liquid flux is applied to a
surface it tends to flow away from the point of application to cover the
largest possible surface area. In a hand-soldering operation, heat is only
applied in a very localized area, and only the flux in the immediate
vicinity is fully heated and rendered inert. So we just say if you add
flux, clean it.
For the no-clean flux in solderpaste that will go through a reflow oven, or
the no-clean flux found within solder wire, that flux does get fully heated,
and does not need cleaning. I believe that a BGA rework operation would
also fully heat any flux underneath the device, so you should not have to
clean what you can't see under the device. However, any flux residue you
can see around the perimeter of the device, definitely should be cleaned.
Hope that was of some help.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Sue Powers-hartman
Sent: May 22, 2007 2:55 PM
To: [log in to unmask]
Subject: [TN] Flux residue, burnt flux
We fight a constant battle with operators leaving burnt flux in joints.
Maybe only a small speck, but drives the inspectors nuts. The way I read
JStd-001D, if they can not see it at referee inspection power, they have to
accept it.
How dangerous is this burnt flux to the PWB? If it's not seen at inspection
power and left on the board, what happens. Also, what about no clean flux?
Our solder training video says that if no clean flux runs out to far and is
not heat activated, it can cause problems. Operators watch this video, but
somehow do not get this. They say that it's no clean, they can leave it all
on.
I keep saying that this can be a problem, and then they ask me, how far out
can the flux be away from the joint before it's unacceptable.
Wow, I'm glad I found this forum, I have so many questions to ask you guys.
Anyway, thanks for the help on this subject.
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