A Conformal Coating is a protective material that "Conforms" to the varied
profile of an electronic circuit assembly.

Ideally, it should be UNDER as well as over, the components.

The best method of applying a Conformal Coating is by dipping. This method is
better able to get underneath devices.
Dipping techniques should be:

In:     < 12 inches per minute so as to ensure that air does not remain trapped
beneath components
Out:    < 6 inches per minute so that the excess material will be pulled off the
surface by the surface tension of the material in the tank.
Dwell:  Only if wound devices are present or where FR2 or paper phenolic
substrates are in use. This is to ensure saturation and proper coverage is
achieved.

Dipping is THE most cost efeective and efficient method of applying any
coating material - BUT...

The circuit NEEDS to be designed for the coating process. (This is why I
posted a question to the Design Forum, to find someone who will include
coating as part of the design software, but no-one replied!? Maybe they will
now??) Masking is a time consuming pain in the tush and that is why many
prefer spraying.

If you can persuade your designer to place components that should not be
coated, on one side of the assembly, then dipping is cheap, effective and
easy. We can dip coat over 200 assemblies per hour using a machine costing
only around $12,000.00 You can't achieve these economics with any other
method!

Paralene is a good product, but the process is worse than dipping: under
vacuum (expensive chamber), vapour deposition (extreme masking demands), low
volume, long process time. Repair and rework is a major pain in the tush and
it absolutely hates being put onto poorly prepared surfaces, dare I say
no-clean.

Spraying ideally needs to be done in a machine. After all, how do you know
someone has coated the board correctly at 9.00am on a Monday morning, 4.00pm
on a Friday much less when they have just had a row with their partner??

It becomes necessary to rely on a meniscus around the component shoulder, to
seal the underside and good capilarity of the coating to get behind the
component legs.

Hope this helps

Graham Naisbitt
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-----Original Message-----
From:   TechNet  On Behalf Of Blanchet,Richard
Sent:   Wednesday, September 24, 1997 5:22 PM
To:     [log in to unmask]
Subject:        [TECHNET] FW: [TECHNET] ASSY: Conformal Coating Coverage

I've never tried dip coating 1B31 but I heard it does a good coverage if you
can control your process steadily. Why don't you consider parylene coating ?
 With this process, you can cover every areas, however hard to reach they
might be.


 ----------
From: owner-technet
To: TechNet
Subject: [TECHNET] ASSY: Conformal Coating Coverage