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View Full Version : Off topic......Question about potting.



James Long
10-10-2006, 11:25 AM
Ok...so I'm working on a project....that I would like to keep my code under wraps.....(sorry this is not the correct place...but you guys are so helpful)....

What consideration(s) should I take into account for potting my project after it is finished?

I know that any high amperage voltage regulators need some cooling...what else?

Also what is the best potting for such a project?

Thanks,

James L

Newzed
10-10-2006, 08:09 PM
Select an epoxy that uses Versamid for a hardener.· Packages at your hardware store with two syringes of equal size normally use Versamid as a curing agent.· Epoxies that use triethanolamine as a curing agent· usually turn out very hard and brittle, whereas the Versamid cured epoxies have a certain amount of flexibility.· Do not cover the metal tab of your VR - leave it exposed to the air.

Sid

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Sid Weaver
Don't have VGA?

Newzed@aol.com (mailto:Module?Newzed@aol.com)
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James Long
10-11-2006, 12:53 AM
Newzed,

I thought there were more important factors for potting electronics, like thermal transfer and such.

Although I have never potted a board before.



James L

Newzed
10-11-2006, 01:12 AM
All potted boards run a bit warmer than the same board not potted.· Potting is not recommended for boards with "hot spots" that produce elevated temperatures.··And ·remember that materials that tend to conduct heat also have a lower insulation resistance.· Potting materials must have a very high insluation resistance to prevent conduction between electrical points, ergo, they are not a very good conductor of heat.

Sid

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Sid Weaver
Don't have VGA?

Newzed@aol.com (mailto:Module?Newzed@aol.com)
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James Long
10-11-2006, 09:08 AM
Hmmmmm....that could be a problem.....my board has some high current regs on it. I may have to make two boards and place the regulators on the other board that will not be potted, or make the regulators stick above the potting compound to place heat sinks....or attachment points.



James L

Newzed
10-11-2006, 07:49 PM
James, make sure you use the highest quality parts available.· Choose "military" over "industrial" and select resistors and caps with the highest heat rating.· Once a board is potted, that's it - no repairs or replacements.

Sid

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Sid Weaver
Don't have VGA?

Newzed@aol.com (mailto:Module?Newzed@aol.com)
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parsko
10-11-2006, 07:54 PM
I have pondered this whole potting question too. Can anyone offer a specific brand/type to use? I have used hot glue for some of my stuff, but really wish to use epoxy. I simply didn't know what to use though.

Sid,

To ask a stupid question, what exactly is the difference between "military" and "industrial"? I gather that the military stuff can handle temperature better, but other than that...???

-Parsko

Newzed
10-11-2006, 08:05 PM
Parsko, the higher temp rating of· military means greater reliability and a greater MTBF (Mean Time Between Failures).

Sid

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Sid Weaver
Don't have VGA?

Newzed@aol.com (mailto:Module?Newzed@aol.com)
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parsko
10-11-2006, 08:11 PM
That makes complete sense. So, it's only a heat thing. I thought there might be more to it.

Thanks,

-Luke

Tracy Allen
10-11-2006, 10:57 PM
I recommend 3M DP270 epoxy potting compound. It is meant specifically for potting electronics. It has very low viscosity when mixed so that it flows into voids. It has a very long working pot life, it is not highly exothermic, it does not expand/contract as it cures (so as to bend components), and it is chemically inert toward circuit materials. And it has a coefficient of thermal expansion that is not too far off from circuit boards and the components. You will surely have to watch out for hot spots. Sometimes encapsulated power packages have a heavy stud or plate on one side, for attaching to an external heat sink. The 3M DP system consists of an applicator gun and mixer nozzles that are a real pleasure to use. You can get it from McMaster-Carr or many other sources. I've also looked into MasterBond products, and I have the feeling that they are probably the best on the market. But they are a little out of reach of the small shop.

Military grade components usually come with a certificate, certifying they have been through a burn in and test process and stating exactly which military standard tests they have been subjected to. You can also tell by the price! It is hard to get to Mars to fix an IC on rover!

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Tracy Allen
www.emesystems.com (http://www.emesystems.com)

Paul Baker
10-12-2006, 01:51 AM
James, do you need to pot the regulators? Couldn't you just pot the nessesary electronics to keep prying eyes away from your code, or create a daughter board for the supply?

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Paul Baker (mailto:pbaker@parallax.com)
Propeller Applications Engineer
[/url][url=http://www.parallax.com] (http://www.parallax.com)
Parallax, Inc. (http://www.parallax.com)

James Long
10-12-2006, 04:57 AM
Paul,

Yea.....sorry you didn't see....I could omit the regs(from the potting)....if possible to isolate....I did comment earlier in the tread that a daughter board may be in order.

There are other reasons for the potting....other than code. I must ensure people do not modify the circuit and also from vibration. I know this won't help the internals of the chips, but will help with the components themselves.

But Paul...thanks for the suggestions.

Tracy.....thanks for the name of a system specifically for potting....that was what I was looking for. Although I could have searched the web, I find personal experience with a product goes a long way.

James L

alex2
10-25-2006, 07:32 AM
I have been looking for cheapest thermally conductive potting compound as well.

My question is, can anyone recommend an inexpensive generic rhyonite or plastic
box manufacturer for small quantities ? My microC-gizmo goes inside this box, the box gets
filled/covered with compound.

Size of the box LxWxH in inches is about 4x2x1.

There has to be a place that would sell one for some like 1-2 $ even in small quantities.

I can not believe how expensive a small piece of plastic can be, based on what I found so far.

Thanks
(sorry about the off-topic)

Phil Pilgrim (PhiPi)
10-25-2006, 07:39 AM
Robison Electronics (http://www.robisonelectronics.com/) sells potting shells. They might be able to help.

-Phil