Thermal epoxy

[zachtheterrible]

I think that's the name of it, and I need some. Just one quick question though: Does this stuff act as a glue, or is it just a grease? And where to get some?

 

[Nigel Goodwin]

I think that's the name of it, and I need some. Just one quick question though: Does this stuff act as a glue, or is it just a grease? And where to get some?

Be more explicit! - what are you wanting to do?.

 

[Oznog]

"thermal grease" or "thermal compound" is grease.
"thermal epoxy" is epoxy thus sticks things together permanently. Arctic Silver is the best (and it's electrically nonconductive). Arctic Alumina, also very good.

 

[justDIY]

Depending on your application, Artic Silver's products may or may not be the best

just to offer a second opinion, MG Chemicals 832TC is a thermally conductive epoxy with excellent specifications.

Its known as an encapsulating and potting compound, designed mainly for industrial electrical and electronic applications.

it is a two-part system, the base and the hardner kept in separate jars .. you mix 50:50 and then you have an hour or so to fiddle with it before it skins ... it is soft like wax in 12 or so hours, and can be shaped easily - by 48 hours it is hard like stone, and requires a great deal of effort to shape

I have used it to encapsulate electronics, in lieu of a formal enclosure. I have also used it to secure electronics to heatsinks.

here are some superflux leds encapsulated in 832tc

**broken link removed**

 

[zevon8]

AAVID also makes thermal epoxy ( well, lots of people do, but anyways ) They have a line called Therm-o-bond, that is very good. It comes in different grades, and be had from Newark and many other big suppliers.

Some of the materials are self-shimming. This guarantees an application thickness across the device.

 

[zachtheterrible]

Thanks for all the replies. Yes, I do want it to stick together like glue.
The application is for a 1W LED. I'm still fiddling around with those :lol:

I tried using regular epoxy to heatsink a 1W LED to the end of a 1/2" steel rod with good results. I left the LED on full power for about 12 hours and it worked fine with no noticable dimming or anything. I wonder how thermally conductive regular epoxy is? This is the kind of epoxy you get from home depot that is used to dowel pieces of rebar into concrete.

Thanks for the help :lol:

 

[justDIY]

i'd say "most epoxies" are better insulators than conductors ... since they're basically just plastic

something like jb weld that has metallic filler in it is a better conductor than an epoxy with plastic filler

the real key to good heat transfer is making your interface as thin as possible ... so polish the end of that rod until it's mirror like, and the same for the back of the luxeon ... then use something like the Artic Silver line of epoxies - that's what they are designed for, very thin adhesive thermal interfaces.

if your rod gives you enough room to tap a few small holes, you could use a thermal grease and screws, improving your mechanical mount and your thermal interface

alternately, look into 3M 9885 thermal interface adhesive tape - I've used some to mount luxeons to aluminum heatsinks, and I must say it works very well. It's been some time now, and the luxeon are still firmly attached.

hmm, doing a bit more google turns up some rather bad news about the 3m tape from Purdue Univ.

**broken link removed**

I do know that my heatsink gets HOT after running approximately 10 watts of luxeons at full output for more than 10-15 min, so the heat must be transfering

 

[Oznog]

Non-thermal epoxy is pretty poor for a Luxeon!

1W is definitely on the low end for performance demands. It'd be a much bigger issue with 3W or 5W devices. You don't mention if this is an emitter or a Star though, them emitter is more demanding:
1. Must have thermal epoxy, not regular
2. The use of thermal tape is discouraged. It doesn't have as good a transfer coefficient.
3. Steel is a poor thermal conductor for this job, especially if it's on the end of a rod. Aluminum or copper is much better.

The Luxeon is rated for this power level only if the back is kept fairly cool. Higher die temps will cause the device to degrade more, perhaps much more, rapidly. The efficiency goes down when die temp goes up. It's difficult to see the power level difference unless side-by-side with a well-cooled identical emitter though.

 

[zachtheterrible]

Well I guess that regular epoxy may not be as good as I thought.
Sorry, I forgot to mention that the LED that i am using is just the plain ol' emitter.

Thanks for all the help, I've got a much better idea of what I'm doing now :lol: