Hi Kenny,
Flux residue left on the board will act as a barrier between the
conformal coating and intended coating surface. While newer conformal
coatings have been designed to better wet soldermasks and small amounts
of remaining flux residue, it is always recommended that full testing be
conducted to truly understand the effect of remaining residue. The
results will depend on variables including the type and amount of
residue present, specific conformal coating. The flux residue barrier
can lead to eventual loss of adhesion or even localized delamination of
the coating in some cases. Cleaning is definitely best practice.
Jon Galaska
DYMAX
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Thursday, March 04, 2010 1:02 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat Over No-Clean Flux
Kenny,
I would clean before I coat. I am no chemist but I would bet $$$ that
whatever it is on the board can interfere with the coating cure/dry
process.
I know that no coating will stop moisture penetration and having voids
or
other material where water can be trapped is really bad. The amount of
water
within the coating is very small and the coating still remains a good
insulator. But if the water meets any ionic source under the coat you
have
conduction at the PCB surface.
If it was me I would rather go through another wash rather than coat
over
the flux and not understand the process.
I do a little silicon spray coat on some boards. I rework with WS flux
then
clean.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ken Bloomquist
Sent: Thursday, March 04, 2010 12:20 PM
To: [log in to unmask]
Subject: [TN] Conformal Coat Over No-Clean Flux
We have a twelve leaded, through-hole component that has to be hand
soldered
on the circuit board. The assembly gets conformal coated with urethane.
We
would like to hand solder these twelve leads using no-clean and then
conformal coat the board. The component would be added as a final step
after
the assembly has first been cleaned.
Since this is not a "total no-clean" process do you see any issues
applying
conformal coat over these twelve no-clean solder joints?
Best regards,
KennyB
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