Upgrading LED, can I use thermal grease instead of epoxy?

[michaelmcgo]

I am changing out the Luxeon III on my Fenix L2T for a Seoul. Can I solder on the new LED with Heat conducting grease behind it, or do I have to use artic alumina (or other thermal epoxy)? Will the solder hold the LED in place by itself?

 

[Kenom]

No. You will want something that is going to hold it in place. Using just thermal grease will hold it in place but the first time you bump it or something else your going to move it out of place. There is a simple formula for making your own thermal epoxy.

just a quick lesson on making your own thermal epoxy.

I don't know if you've looked for thermal epoxy to purchase but the stuff is like gold and almost impossible to find. I havn't been able to find anything with the exception of actic silver thermal epoxy. (I use this stuff as it's the best.) But when you have run out of arctic silver and need to epoxy something down that needs to have thermal transmission characteristics here is a simple do it yourself recipe.

Find yourself a epoxy with a high viscosity. I myself use a 5 minute epoxy that I bought at my work from permatex. I wouldn't recommend using a 60 second epoxy as you have to mix in other stuff to give it the thermal properties.

You will also need a thermal paste or grease. The paste or grease you use is not really the issue other than it's thermal properties. Hence the reason I use arctic silver. Thermal efficiency is different than electrical efficiency. Silver works best then copper then aluminum. I've no idea the composition of the White thermal grease so can't comment on it's thermal properties.

Once you have both the thermal paste and the epoxy you will mix the epoxy according to the manufacturers instructions. 1 strip 1inch long of the activator and 1 inche long strip of the hardener (can't remember the two parts names right now as mine are in a tube you just depress.) Mix the two together and you will get a circle of epoxy about the size of a quarter. Now honestly if this is the size your going to have it is going to be waaay to much for most applications however I am using this as a size comparison so that you can get an idea of how to make this. Once you have your quarter sized mixture of epoxy you will mix in the exact amount of size worth of thermal paste. one quarter size + one quarter size. Mix the two together and you have Thermal epoxy for use on anything you want. I recommend using smaller sizes for use.

 

[Darell]

No. You will want something that is going to hold it in place. Using just thermal grease will hold it in place but the first time you bump it or something else your going to move it out of place.

Just for variety, I'm going to answer the other way.

Yes. It will work fine. (that is, provided that it is soldered to something that is fixed.) I've done countless mods where I stuck grease behind the emitter, and then soldered the leads to a glued-down emitter board (in Alephs). Works great, and makes later replacement a snap. Since there is none of the bonding agent in the way to dillute the heat-transfer paste, it should be more efficient as well. The only down-side is that it is tough to keep everything centered while you are soldering. Sometimes I've had to take a couple of stabs at it.

 

[michaelmcgo]

Thanks guys. I have regular epoxy and thermal grease, so I'll do it that way. How do you guys make sure the LED is perfectly centered?

 

[Illum]

Oh man! a reply from the great man himself, you should see some of the mods Darells done:devil:

I don't know if you've looked for thermal epoxy to purchase but the stuff is like gold and almost impossible to find. I havn't been able to find anything with the exception of actic silver thermal epoxy.

I dont know of any other thermal epoxy except the arctic alumina, what properties are you expecting?

michaelmcgo, thermal grease is good for removeable units for testing purposes such as CPUs or LED testings. But in order to be used in modding, either the "Darell method," or engineer a retaining collar for the die:huh:

Thanks guys. I have regular epoxy and thermal grease, so I'll do it that way. How do you guys make sure the LED is perfectly centered?

erm, having never replaced a led before Im not sure...
I would suggest setting it in the thermal paste and lighting up the LED first, and using the reflector to "see" whether the beam is focused, and once you feel its in the right spot, make 2-3 marks around the led using a sharpie or a stamp if you have one, that tells you where you should lay the epoxy

 

[wasBlinded]

I've used Darell's method many times with good results.

If you want to make your own thermal epoxy, get some alumina powder from the Sandwich Shoppe and mix it into your epoxy until it has a peanut butter consistency. I can't imagine adding a grease based compound (thermal grease) to expoxy does much for its bonding properties, though it may serve well enough.

 

[Mr_Light]

If I am using Stars rather than emitters I try to use thermal grease and screws to attach them. This may involve some drilling and tapping or nuts and bolts. I really like the option of swapping out stars when I do things like wrench the dome off of a CREE star while trying to attach a CREE optic!