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From: Larry Kent on 6 Mar 2010 23:09
Is it possible to use epoxy or polyester surfboard resin for potting
audio fequency PCB's?

How about the crystal epoxy used for encapsulating insects, etc?

Any other low cost alternatives, aside from flexible rubber/silicone?

Many thanks,

Larry Kent


From: D from BC on 6 Mar 2010 23:44
In article <4b932620.4739000(a)news.tpg.com.au>, larrykent(a)raglands.com
says...
>
> Is it possible to use epoxy or polyester surfboard resin for potting
> audio fequency PCB's?
>
> How about the crystal epoxy used for encapsulating insects, etc?
>
> Any other low cost alternatives, aside from flexible rubber/silicone?
>
> Many thanks,
>
> Larry Kent


I tried a solvent based 2 part epoxy mistint sold for cheap at a paint
store.
It only dries in thin film as it's supposed to.
I tried potting and it was still gooey after 1 week.
The gooeyness could be from solvent getting trapped by the skin that
forms. iows.. The epoxy paint self-seals extending the cure time.
That or the paint was overtinted. Was blue.
So don't try that.
Solvent based epoxy paint is different than 100% solids epoxy or the
type used for glue.

Maybe try 100% solids epoxy for floors??


--
D from BC
British Columbia
From: Kevin McMurtrie on 7 Mar 2010 00:17
In article <4b932620.4739000(a)news.tpg.com.au>,
larrykent(a)raglands.com (Larry Kent) wrote:

> Is it possible to use epoxy or polyester surfboard resin for potting
> audio fequency PCB's?
>
> How about the crystal epoxy used for encapsulating insects, etc?
>
> Any other low cost alternatives, aside from flexible rubber/silicone?
>
> Many thanks,
>
> Larry Kent

Don't use general purpose epoxy or polyester! Some formulas will sweat
compounds that are corrosive and conductive. Formulas meant for fiber
composites can get so hot in large volumes that they'll incinerate
themselves.

You can buy electronics potting compounds at online electronics stores.

Conformal coatings can provide water and dirt resistance without making
the circuit impossible to repair. Aerosol cans of pure urethane from a
hardware store seem to work well too. I haven't seen urethane attack
anything yet and adhesion is pretty good.


Avoid 3M Scotch Weld Epoxy Potting Compound because it has extremely
poor adhesion. It forms beads in thin films and it cracks away in thick
films. Either way your project is ruined.
--
I won't see Google Groups replies because I must filter them as spam
From: D Yuniskis on 7 Mar 2010 00:52
Hi Larry,

Larry Kent wrote:
> Is it possible to use epoxy or polyester surfboard resin for potting
> audio fequency PCB's?
>
> How about the crystal epoxy used for encapsulating insects, etc?
>
> Any other low cost alternatives, aside from flexible rubber/silicone?

What are your *goals* in potting the circuit ("protect" IP, prevent
tampering, environmental extremes, etc.)?

Also, what other criteria affect your choice of compounds (e.g.,
thermal properties, weight, etc.)
From: Dave Platt on 7 Mar 2010 01:17
>Is it possible to use epoxy or polyester surfboard resin for potting
>audio fequency PCB's?
>
>How about the crystal epoxy used for encapsulating insects, etc?

Polyester resins often heat up a lot, and shrink, when curing. That's
not necessarily a problem when fiberglassing a surfboard, but it can
put a serious stress on components during encapsulation - might crack
'em loose from the board in a really severe case. I believe this
tendency can be reduced somewhat by using a slower curing cycle (less
catalyst per amount of resin).

Some of these resins remain somewhat sticky when cured, and need a
topcoating or upper layer containing a surface-hardening agent or wax.

You can "stretch" epoxy used for potting, and save quite a bit of
money, by loading it up with a filler before pouring. I've
encapsulated small circuit boards in TAP Plastics' slow-cure marine
epoxy, mixed with fine dry sand... cheap and effective, if rather
heavy and prone to settle out during the curing process. Glass
microspheres are much lighter, don't form as hard a matrix, and are
rather more expensive :-(

--
Dave Platt <dplatt(a)radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
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