Black coating or casting

[BlackSportD]

I've seen proto boards protected or covered in this black tar like goop. Where can one find this for personal use? Or better yet how does one make a home made cast like process where the little circuit card is encased in a "box" made from a liquid?

 

[dknguyen]

It's called potting compound or epoxy. I think you just stick it in a mold and fill it up and remove it from the mold later...I'm not sure what materials it won't stick to.

What do you need it for? It pretty much doesn't allow any fixing or modification after it's applied and can stress components. Are you sure you can't just use something like a silicone or acrylic conformal coating spray? It forms a thing layer (hard if acrylic and rubbery flexible if silicone) over the PCB to protect it from the elements and shorts, etc.

If I'm not mistaken there's plastic hard stuff and there's also stuff that cures to a nice thick rubbery coating (not sure if this is considered epoxy or not).

YOu can find it in the chemicals section at electronics store or radioshack maybe. YOu might be able to use the regular epoxy at the hardware store too though I am not sure.

I've seen very nice results (commercial of course) where they had 5-sided plastic shell for the PCB (not oversized or too deep of course, and they just fill it up and the whole things bonds together.

 

[justDIY]

you've withheld your location, so who knows whats available in your area.

here's some of my experience with potting epoxy:

https://projects.dimension-x.net/archives/3
https://projects.dimension-x.net/archives/2

 

[BlackSportD]

That last coating sounds good, if it comes in flat black I'll like that. Can I get the spray from any electronics store or Home depot?

Its for a 555 timer circuit that audioguru greatly helped me with (thanks again). I doubt it makes enough heat or is unreliable to the point of being afraid of completely covering it up. I've noticed with O2 sims for cars which are 555 oscillating circuits, they usually come as a solid plastic'ish box with wires sticking out. Wanting to cover my circuit in a similar fashion for clean look and protection.

 

[BlackSportD]

you've withheld your location, so who knows whats available in your area.

here's some of my experience with potting epoxy:

https://projects.dimension-x.net/archives/3
https://projects.dimension-x.net/archives/2

Let me update my location, must have been in a rush when I registered. I'm in Los Angeles.

 

[dknguyen]

Here's the stuff that you spray to stop the epoxy from sticking to the mold, whatever it may be:
**broken link removed**

The conformal coatings do not form a hard box since they are not potting compounds. They use air or whatever to cure so they can't be thick like a box and do not provide mechanical support. They do not make things "explosion proof". They are meant to protect from moisture, mild abrasion, chemicals, and electrical shorts. They are more similar to varnishes on a table top. Their advantage is they are one-part and can be a spray or brushed applied or dipped, etc. They are usually clear.

Most potting compounds are two-part solutions that start to cure when mixed so they cure in the absence of air (though I think some cure with UV light...somehow at those thicknesses). Epoxy usually increases thermal conductivity since air is a terrible thermal conductor. Epoxy can also affect timings. Not sure why but where I work whenever something is epoxied up delays (in particular power up times) are increased. usually this is noticed in code where one device must wait for another to power up. These are meant to physically encapsulate the PCB in a block.

If you need mechanical support you can't use the conformal coating and have to go with the epoxy.

 

[BlackSportD]

Thanks everyone, off to the stores.

 

[justDIY]

maybe a place like Fry's would sell this stuff. it's pretty unique, you'll likely be getting it online... I bought mine from circuit specialists

they do sell a black epoxy adhesive in stores, it might work, if you can be patient and apply it in layers. a thick layer of it will take forever to cure, and will likely bust your solder joints. as an adhesive, it's designed to shrink a large amount when it cures, to draw the item being glued together. as a potting compound, it'll just tug at all your solder joints.

use wax or HDPE as a molding substance, and you won't have to worry about using a release agent. or you can use regular plastic and something like cooking spray as a release agent. a metal mold could be coated with wax pretty easy (blowtorch and odd chunks of wax)

good luck!