# Homemade heatsink epoxy



## qwertyydude (Nov 20, 2008)

I didn't know where to post this but if you ever need to make heat sink epoxy, which I needed for some projects of mine, a good way is to use a sanding drum and sand a block of copper. I used a fine 320 grit drum on my dremel. And using light pressure I sanded a small block into a pile of dust. To make the regular 5 minute epoxy as heat conductive as possible I mixed as much copper dust as possible into 5 minute epoxy as to saturate it into a thick almost non adhesive paste. Applying this as thinly as possible and wringing the two objects to squeeze out air and excess epoxy and applying pressure until dry resulted in the led star making incredible thermal contact with the heat sink plate. 

For comparison I used a regulated, overdriven 1.4 amp R2 led on a star. This is attached to a black anodized heatsink with the anodizing sanded off the base where it makes contact. I maxed out the test at 130 degrees. The artic silver epoxy reaches 130 degrees in about 3:30 minutes, my custom mix reached it in about 3:10 minutes. I'd say a significant improvement.

Now this is only good for non electronic uses because this stuff is actually conductive, I measured a direct ground from the star to the heatsink base. But since it is electrically conductive you know it has to be a nearly ideal heat conductor since it is made of copper. It's got to be at least as effective as soldering for heat conduction. Plus it is really really cheap to make. So if anyone is interested here's a cheap way to heatsink stuff.


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## KowShak (Nov 20, 2008)

qwertyydude said:


> It's got to be at least as effective as soldering for heat conduction. Plus it is really really cheap to make. So if anyone is interested here's a cheap way to heatsink stuff.



Solder has thermal conductivity in the 30-80 W/mK range. Arctic Alumina (a thermal epoxy) has thermal conductivity of about 0.3 W/mK. I think it unlikely that your homebrew epoxy would outperform solder, solder (metal on metal) is a pretty good way of joining components, thermally speaking.

However, the fact that it outperforms Arctic Alumina means it is worth making, especially as its cheap to make.


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## Sgt. LED (Nov 20, 2008)

Thank you for posting this!

Gets the gears turning............


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## PCC (Nov 20, 2008)

qwertyydude said:


> I maxed out the test at 130 degrees. The artic silver epoxy reaches 130 degrees in about 3:30 minutes, my custom mix reached it in about 3:10 minutes. I'd say a significant improvement.


Sorry, folks, I'm left scratching my head on this one. Was that 3 hours and 30 minutes for the Arctic silver and 3 hours and 10 minutes for the custom mix to reach 130 degrees?


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## qwertyydude (Nov 20, 2008)

No it's 3 minutes 30 seconds for arctic silver and 3 minutes 10 seconds for my homemade stuff.


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## KowShak (Nov 21, 2008)

qwertyydude said:


> No it's 3 minutes 30 seconds for arctic silver and 3 minutes 10 seconds for my homemade stuff.



What were you timing? Could you describe the setup better? Was it the time for the heatsink to reach 130 degrees or the time for the LED to reach that temperature?


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## qwertyydude (Nov 21, 2008)

It's the time the heatsink reaches 130 degrees.


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## yellow (Nov 21, 2008)

both Thermal Epoxy as well as the homemade thermal epoxy are something to be skipped.

Try the whole thing again, but with the only good way of mounting: 
*thermal PASTE *instead of thermal glue, 
when the Star is placed at the spot where it belongs, use Epoxy around the Star to fix it, or (better) some screws into the mounting plate.

that way: 1st of all: much better thermal path, 2nd: cheaper, 3rd: the emitter/star can be placed and checked for correct positioning and replaced without any time pressure


... would really like to know it that setup reaches the temp even quicker than the homemade thermal, theoretically time should decrease considerably


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## qwertyydude (Nov 21, 2008)

It really won't decrease considerably, you have to consider that the heatsink itself has a thermal mass and will take time to heat up. I'll run the test using a bare star and thermal paste and time it, though I doubt it'll heat up any faster considering the star didn't feel much hotter than the base.


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## trout (Nov 21, 2008)

I can see a really good use for this apart from fixing stars 

where you are fixing a heatsink slug in to a tube and a cheap epoxy copper mix sounds great .


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## KowShak (Nov 22, 2008)

trout said:


> I can see a really good use for this apart from fixing stars
> 
> where you are fixing a heatsink slug in to a tube and a cheap epoxy copper mix sounds great .


 
I think the ideal way would probably be to thread both the tube and the heatsink and have them screw into one another. For those who have access to a lathe and know how to use it, threading is an option. For those who don't, thermal expoxy is better than non-thermal glues or nothing at all.


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## Justin Case (Nov 22, 2008)

See

http://63.74.115.230/tips683/


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## Oznog (Nov 25, 2008)

There's a big difference in total thermal conductivity with layer thickness. And it's hard to give an exact figure for what thickness a thermal epoxy layer will be since it depends on temp and pressure and surface regularity. For a given material conductivity, half the thickness is half the resistance and I don't doubt that that good prep and pressure the thickness could be halved over basic gluing.

BUT... particle size does present an absolute limit. AS uses a very fine grain of silver particles. Sanded copper... hard to say but probably much larger. This may create a limiting factor on how thin the layer can be laid even with pressure.


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## qwertyydude (Nov 25, 2008)

It is true that smaller particles may allow a thinner layer to conduct heat, but the property that differentiates my compound from the arctic silver is electrical conductivity. It may be useless in sensitive electronics because it can short stuff out, but in leds which are regularly soldered to heat sinks the particles which bridge the star to the heatsink base with electrical conductivity also greatly enhance heat conduction.


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## VegasF6 (Nov 26, 2008)

I would think your copper dust mix would be contaminated with large grains of whatever material your sanding disk was made of. Probably zirconia alumina or zirconia oxide. 

But, there is no arguing with results, interesting experiment, and good job.

I think if I really wanted to mix my own I would look to purchase copper dust, or even diamond dust, but that is too much labor for me 

FYI make sure you are wearing some sort of particulate filter mask or something, and goggles. Copper dust can be harmful.

http://www.eco-usa.net/toxics/copper.shtml


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## qwertyydude (Nov 26, 2008)

Actually it's aluminum oxide so no more harmful to heat conduction than anodizing, plus I made sure to use light pressure, there was hardly any wear on the drum so I think contamination was minimal.


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## Oznog (Nov 26, 2008)

qwertyydude said:


> in leds which are regularly soldered to heat sinks the particles which bridge the star to the heatsink base with electrical conductivity also greatly enhance heat conduction.



Electrical conductivity doesn't create thermal conductivity.
Copper is slightly worse than silver for thermal conductivity too.

I think you're going on the idea that if there's electrical conductivity then you have copper touching thus making a straight thermal path. It doesn't mean it'll have high thermal conductivity too. The path will be so thin it may have a very low conductivity.

In short I don't see how this is going to compete with Arctic Silver which studies particle size and end thermal conductivity very carefully. It's not expensive when you factor in that you use very very little in this application.

I'm kinda done with these non-solderable bases anyways. Solderable stuff is da bomb.


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