Jim

What types are there?

Acrylic - Polyurethane - Silicone - Epoxy and many specials/mixes. Air
curing, moisture curing, heat curing, UV curing or combinations of these.
Materials may be solventless 1 part, low or no VOC solvent based, or good
old fashioned "takes the paint off your decks if you have a boat".

How easy are they to apply?

In most cases easily but there are tricks to every trade. e.g. Ideally a
coating should be 1 component - fast curing - long stable pot life - easily
reworkable  (for example you may want to get it off the floor when you spill
it!) Applying such materials may be done using dip techniques, spraying,
dispensing or brushing.

Ideally a coating should be under as well as over the components to maximise
the available protection thus dipping is usually the most efficient and
economic method of application. However, this may be too expensive because
of the amount of component masking that may need to be done. For this
reason, either selective coating methods using robotic dispensing can be
used or conventional spray systems where masking is reduced to a shield
rather than a barrier can be employed.

What will it cost?

Depends upon a number of things but you could pay less than £0.05 ($0.08)
per board all-in including capital and material. On the other hand, it could
cost you more than £30 ($50) if the total masking/de-masking and rework time
exceeds 1 hour per board. The material is the smallest part of this equation
as you SHOULD be able to coat around 150  6 inch x 3 inch assemblies per US
quart or 1 litre. Bear-in-mind that the prevailing US MIL-I-46058 spec
recommends 0.001 inches to 0.005 inches coating thickness in the cured
state. We have a simple computerised cost model for this if anyone is
interested.

Is it possible to remove after application for rework (spillage) etc.?

All coatings are repairable however, a hammer and chisel may be considered
too severe. Acrylics are generally more easy to repair than others because
they may be dissolved by relatively mild and environmentally benign
solvents.

I hope this helps you but we do have a lot more. Lest I be accused of
spamming, let me know off line and I will send you more and any other
Technetters that may be interested.

Graham Naisbitt

__________________________________________________________________________

[log in to unmask]

Concoat Ltd
Alasan House, Albany Park
Camberley GU15 2PL UK                        http://www.concoat.co.uk

Application Engineers in Chemical Compounds to the Electronics Industry

-----Original Message-----
From: Jim Hedderick <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 19 January 1998 16:29
Subject: [TN] CONFORMAL COATINGS ON PCBS


>I have just been asked a question about conformal coatings on printed
circuit boards
>and I can remember this question arising on this forum some time in the
past.
>I would again like to bring this subject up to try and find out some of the
following answers.
>The board I wish to apply this coating to is to be used in a high humidity
environment
>
>(I) What type of conformal coatings are available ?.
>
>(ii) How easy is it to apply?.
>
>(iii)  What will it cost?.
>
>(iv)  Is it possible to remove after application for rework etc?.
>
> Thank you
> Jim Hedderick
>
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