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I can successfully protect a 30 Mohm impedance circuit from standing
water (at 120 V) using a sprayed silicone coating for a couple of
minutes using one of several coatings. Silicones work the best.
______________________________ Reply Separator _________________________________
Subject: Re: conformal coating help
Author: [log in to unmask] at internet
Date: 1/22/97 8:00 AM
<< We need to provide 100% moisture seal on the top surface of some FR-4
boards
about 8"x12" that have SMT components mounted. Can I do this "easily"
in-house without much equipment? What materials and suppliers? We could
easily install a fume hood if necessary. This is not a high volume project.
What do I do about sealing vias?
thanks, Crawford Byxbee >>
Crawford,
There is no such thing as a 100% moisture seal with conformal coatings. All
of them are organic polymers, which have varying levels of moisture
permeability. Water WILL get through, it is only a matter of when. Better
to ask the question of why you feel you need to have a 100% moisture seal.
Of the available coatings, you should probably try a silicone (type SR)
coating or parylene coating. Since your volume is low, sending the product
off for parylene coating, avoiding capital investment, may be your best bet.
You might also consider a contract conformal coater.
Doug Pauls
CSL
[log in to unmask]
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