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Sealing circuit boards with silicone

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mick H02/03/2020 09:58:43
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I have been advised that I can effectively seal and waterproof electronic circuit boards with silicone. The specific application is for a small (1.25" x 1.25" board for a boiler water level sensor for a model steam boat. My query is that tube silicone usually has a strong acetic acid type smell and I wonder whether it will corrode the connection wires etc ? Otherwise it seems to be a good idea. As an alternative there is always shrink wrap but I think the silicone could provide a neater job.

Mick

Michael Gilligan02/03/2020 10:03:16
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16229 forum posts
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There are better products available, Mick

... Do a search for ‘Conformal Coating’

MichaelG.

Mike Poole02/03/2020 10:04:05
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There are versions of silicone for electronic work, I would not use a kitchen bath sealant.

Mike

Nick Clarke 302/03/2020 10:11:59
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861 forum posts
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Subject to choosing an appropriate silicon yes - Many thousands of Lucas ACR car alternators had the diodes sealed in silicon and the tripler in a CRT TV or monitor was often similarly sealed - I used to dig out the sealant from both of these to replace (non-replaceable!) parts.

Joseph Noci 102/03/2020 10:37:24
739 forum posts
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Don't use any sealer using acids or alkalies as curing agents. All non-nobel metals corrode when embedded in that stuff! Many Electrical supplies sell a conformal coating spray for electrical switch boxes, or a better type is often available from an Auto-Electrical supplier - often used to insulate/seal alternator/generator windings - typically a red spray. Conventional Electronic conformal sprays are available from places like RS components, etc, but pricey.

If the board is not exposed to temps greater than 80degC, then a decent clear lacquer spray will do the job. Won't last years as will a good conformal coating, but maybe good enough?

Make sure the board is really clean - clean with dishwashing liquid and water, rinse, dry, bake in the oven at 50degC for a while - 20min, and spray 4 or five thin coats from every angle.

Joe

norman royds 202/03/2020 11:56:38
48 forum posts

I would sugest silicon for fish tank I think it is acid free norm

Steviegtr02/03/2020 12:19:31
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1391 forum posts
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Or contain it in resin. Available from many places inc car accessory shops.

Steve.

Bazyle02/03/2020 12:45:07
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5400 forum posts
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Double glazing sealed units are supposed to be put in with non-acidic sealant. You might see if an installer will give you the end of a tube.

mick H02/03/2020 13:51:35
723 forum posts
21 photos

Thanks for the advice gents. I am pleased that I asked.

Mick

Steve Skelton 102/03/2020 13:54:38
77 forum posts
3 photos

Mick, having worked with silicone rubbers in the window industry the type of silicone you are looking for is "neutral cure low modulus" silicone sealant.

Steve

old mart02/03/2020 17:08:50
1927 forum posts
151 photos

You can get electronic potting compound for this, or an acetic acid free silicone from Dow Corning.

Don't forget, that sealing will affect any heat sinks adversely.

Edited By old mart on 02/03/2020 17:10:51

Neil Wyatt02/03/2020 17:44:42
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Posted by mick H on 02/03/2020 09:58:43:

is that tube silicone usually has a strong acetic acid type smell and I wonder whether it will corrode the connection wires etc ?

The answer is yes, there are special types.

An easier to use and more effective solution is hot melt glue!

I used this when I modified my DSLR to have a cooled sensor to protect the cricuit board from condensation and ice, and it worked perfectly.

Neil

duncan webster02/03/2020 19:51:47
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I used hot melt glue to pot some resistors recently (for track circuiting) A lot easier than messing about with 2 pack resins, especially for a small amount

Martin Hamilton 102/03/2020 20:03:50
179 forum posts

Yes hot melt glue will do the job, you can also use Plastidip also. Def do not use any of the acidic silicons like the bathroom & kitchen types. if using silicon use electronics grade silicon, You can also seal with a thin coat of 2 part epoxy glue.

Brian Oldford02/03/2020 20:06:57
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684 forum posts
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Posted by duncan webster on 02/03/2020 19:51:47:

I used hot melt glue to pot some resistors recently (for track circuiting) A lot easier than messing about with 2 pack resins, especially for a small amount

track circuiting what pray tell?

duncan webster02/03/2020 20:48:02
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Posted by Brian Oldford on 02/03/2020 20:06:57:
Posted by duncan webster on 02/03/2020 19:51:47:

I used hot melt glue to pot some resistors recently (for track circuiting) A lot easier than messing about with 2 pack resins, especially for a small amount

track circuiting what pray tell?

a 5"g railway of course. If you're interested send me a pm and I'll find the relevant ME articles

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