help - need encapsulant?

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ralphpage
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help - need encapsulant?

Post by ralphpage » Mon Mar 15, 2004 12:24 pm

I know in a old issue of Nute & Volts there was an article that included the author potton (conforma coat) or encapsulating the circuit board, This stuff is also good for tool handles - can any one help me find the article, or know of the name of the encapsulant ?

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Edd
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Re: help - need encapsulant?

Post by Edd » Mon Mar 15, 2004 3:56 pm

I don’t have my archived issues at this site, but with your mention of “tool handle dipping” , one must certainly suspect the product to be a liquid vinyl product.Such as one can currently find at hardware stores, initially available in RED and then I saw BLUE available, but the kicker in PCB use would be that one would want the clear, uncolored, mix.
Ref:….. http://www.michaelholigan.com/Departmen ... _id=ath601<p>So, apparently you are wary of a subjection of your PCB to potential water/humidity/dust/fungus in its environment.
I suspect I’ve seen the evolvement of the art throughout the years.60 years back on antique radios and old military gear either shellac or varnish was used….or even Beeswax in specific applications. Then later in commercial, military, and at NASA, the use of acrylic lacquer, then the use of polyurethanes, epoxies, and silicone rubber. If rework was required on the acrylics family….. acetone,xylene,toluene or MEK would dissolve/access the problem area. On the high density polyurethanes one could just cut out a square and peel the coating off in the rework area as a sheet.
Then there was the dreaded and tenacious epoxy coatings, they could be done by building up a wax dam and then utilizing a timed soaking of phenolic acid on the surface. The coating would craze and become very brittle and then a fine needle would chip up the coating for its removal.In the eighties Dow Corning got real creative with some of their potting compounds where some just resembled a dense clear Jello, you just probed in around your work area and popped the encapsulant out as pieces.
Since the seventies my conformal coating of choice , if required, is the clear acrylic lacquer spray can product of Krylon…but seems like Elsie the cow has her udder in it…Bordens. I think the Krylon trade name is retained. The specific blend is what they call Crystal Clear. Never any problems with it . The only thing one might encounter is runs if you get overzealous, I just always had the board flat and sprayed down onto it. Also if too humid when applied the coating tends to take on a milky white appearance. I preclude that and also got a super quick drying time by preheating the PCB with a heat gun.
On construction projects,that’s what I also use on polished ( with Brasso) aluminum front instrument panels as the last step…..they look as if being brilliantly chrome plated.The side cabinet panels are usually walnut or red oak.<p>73's de Edd
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Chris Smith
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Re: help - need encapsulant?

Post by Chris Smith » Mon Mar 15, 2004 4:52 pm

For a permanent covering, I use Boat finishing resin, with a cold mix that take about 24 hours to cure. Lasts longer, no shrinkage, and no yellowing? A cold mix is one using less than the recommended MEK-p curing agent. Clean the board with Methyl alcohol before applying and warm under a lamp to completely dry.

amuron
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Re: help - need encapsulant?

Post by amuron » Mon Mar 15, 2004 10:12 pm

Emerson and Cuming is the outfit I usually turn to for encapsulants. They have a wide range of materials, and are liberal with samples.<p>http://www.emersoncuming.com/<p>Thanks
Ron

Dean Huster
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Re: help - need encapsulant?

Post by Dean Huster » Tue Mar 16, 2004 4:40 am

Never really thought of it until now, but I wonder if good ol' spar varnish (spar polyurethane) would make a good "poor man's" conformal coating for boards? A few swipes with a brush and presto! You could even use water-borne if you slip the board into a 150° oven for several hours to dry the water out. In either case, a warm oven will speed dry time.<p>Just don't forget that any conformal coating may alter dielectric constants enough that RF boards may have a frequency shift that may require realignment.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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haklesup
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Re: help - need encapsulant?

Post by haklesup » Tue Mar 16, 2004 1:29 pm

While almost any coating (including varnish) will provide a suitable mechanical barrior, you may be unhappy with the electrical performance of some coatings such as dielectric withstanding voltage or the leakage caused by additives or uncured material.<p>You also should consider what happens if you ever need to remove the coating. What will the solvents do to your assembly etc.<p>Check out this detailed tutorial link on this page on conformal coatings Dow Corning Conformal coatings page

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