Cheap potting alternative

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??

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.

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 :-(

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

On a sunny day (Sat, 6 Mar 2010 22:17:50 -0800) it happened snipped-for-privacy@radagast.org (Dave Platt) wrote in :

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

D from BC wrote in news:MPG.25fccf14e30ab03e9896c8@209.197.12.12:

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.

snipped-for-privacy@raglands.com (Larry Kent) wrote in news: snipped-for-privacy@news.tpg.com.au:

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

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

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.

Fine grain fiberglass "powder" (shards) makes an excellent filler as it also makes the media a better thermal conductor.

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!

You're retarded.

You're a pussy too.

And, you are a goddamned liar as well.

Only for completely brainless lying fucktards like you.

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.