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
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
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.)
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 <dpl...@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!
>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 :-(
>
A friend suggested surfboard epoxy, but with the foam powder that they
use for ding repairs mixed in. Lighter than sand, athough not a tough
I suppose. The "give" it provides apparently cushions the parts during
curing.
Does that sound feasible?
Larry Kent
>>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 :-(
The electronics in my outside located satellte TV dish motor controller
seems to be covered with some wax, parafine perhaps.
It does make it insensitive to moist it seems, been working OK for years,
in spite of the fact that my scope probe pricked holes in the wax at some points
when I was figuring out the circuit ;-)
Wax.
--
Boris
epoxy cures by a thermal reaction;it can get pretty hot,especially in thick
applications.
Some folks discovered this when the plastic tub of epoxy they mixed up
melted from the heat of the reaction.
--
Jim Yanik
jyanik
at
localnet
dot com
you can buy phenolic microballoon fillers at marine stores,where you will
find quality boatbuilding epoxies like West systems.
Lightweight,yet easy to machine.
=fuel
RL
How about, don't pot it. It is a low cost alternative you may not
have
considered.
I have seen boards potted in stuff that was basically tar. At about
100C
the stuff would melt and become a sort of sticky goo.
Cheapest alternative: don't pot - it's messy, insecure,
environmentally unfriendly, and makes service and repair just about
impossible.
Unless you intend to make it part of the surfboard, in which case you
should consider a sealed enclosure.
--
Joe
>>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).
One can also reduce this issue by conformally coating the PCB first.
That way, no potting compound migrates between SMT parts and the PCB ,
which is where these shear forces occur.
>
>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.
Fine grain fiberglass "powder" (shards) makes an excellent filler as it
also makes the media a better thermal conductor.
> 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 :-(
One can go to nearly any automotive machine shop, and can usually buy a
handful (or a quart sized volume) of glass beads used for grit blasting
purposes. You need to buy it from a newly opened bag that has not been
added to the grit blaster yet.
Tar.
Bwuahahahahahaha!
>On Mar 6, 11:09�pm, larryk...@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
>
>Cheapest alternative: don't pot - it's messy,
You're retarded.
> insecure,
You're a pussy too.
>environmentally unfriendly,
And, you are a goddamned liar as well.
> and makes service and repair just about
>impossible.
Only for completely brainless lying fucktards like you.
>Unless you intend to make it part of the surfboard, in which case you
>should consider a sealed enclosure.
He should at least never consider considering any of your suggestions.
Yes. I have seen candlewax (microcrystalline wax from one of the big
oil companies) used to pot a fm microphone circuit. It seemed pretty
practical to me.
In the olden days potting tar was used, and often still is. Very cheap
but I wouldn't know a distributor anymore. However, it is not very
pretty if that's what you are after.
--
Regards, Joerg
http://www.analogconsultants.com/
"gmail" domain blocked because of excessive spam.
Use another domain or send PM.