Whats the best thermal compound?

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Bort
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Whats the best thermal compound?

If i want to someday build an XM-L2 on copper high amperage light, i want the best heat transferring compound, so please toss in your suggestions

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Rezolution
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Arctic Alumina or Fujik

ezarc
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If you can screw it down then a good cpu thermal paste will probably be the best.

If it also needs to stick it there then I couldn’t say its the best but Fujik does the job well. It will cure like silicone if you ever want to remove it as well.

bose301s
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Rezolution wrote:
Arctic Alumina or Fujik

No and hell no.

Look up Parker Chomerics, PPTk recommends them and I had good luck with their products for an internship project.

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Wakefield deltabond 155Laughing.

Old-Lumens
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If the copper and the heat sink are lapped and the two bolted together, then a good thermal paste would work fine.

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rojos
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Look here: http://budgetlightforum.com/node/13413#comment-233314

PPtk says Wakefield for adhesive, Parker for grease.

And like OL said, lap the mating surfaces.  The condition of the mating surfaces will impact performance more than your choice of compound.

Hikelite
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Rezolution wrote:
Arctic Alumina or Fujik

Fujik(BAB 900) is 0.88W/m.K, that is  poor to say the least.

Hikelite
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Arctic MX-2 is appreciated in the CPU world. It does not have a curing time like AS5. But as will all thermal compound greases you need pressure for the best performance.

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Shin-Etsu MicroSi G751 is probably one of the best I’ve used.

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This Shin-Etsu X23 paste looks good in this ranking. Basically they are all very close.

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Does anyone here actually use screw for the star? Just curious. Any good tools for threading?

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ezarc
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Pulsar13 wrote:
Does anyone here actually use screw for the star? Just curious. Any good tools for threading?

I don’t myself but you can get a basic tap and die set for about $15-20, a good set could cost in the $100s.

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I’ve never needed a tap to put little screws in aluminum…just use the screw as you would a tap.

Copper is a different story, and trying to do that same thing is a good way to shear the head off a screw and leave the body in your hole |(

anyway, they’re cheap enough individually to be worthwhile. pick the screw you’ll use first….
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I once thought this idea:
If you have a Copper LED star and Brass pill – maybe can use the soldering between them? It has a much better heat transferring.

If anyone has tried it? Smile

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I’ve been planning to.

but, I don’t think it has better heat transfer than well lapped parts

http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/

it does preclude the need for glue or screws though…

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I vote for toothpaste – cheap, clean and minty fresh.

I almost always lap my stars+base, then screw them down (usually 4-40 taps and screws). Thermal transfer is so good that I struggle to solder the wires onto the star. In this situation, thermal pastes are a much of a muchness – the cheap chinese stuff seems to work as well (qualitatively) as the Chomerics sample I got. However, the Chomerics stuff is much easier to apply and spreads out more evenly, so if you can sweet talk them into a sample go for that.

No idea on adhesive thermal compounds though, as I’ve never used them.

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dthrckt wrote:
I've been planning to. but, I don't think it has better heat transfer than well lapped parts http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/ it does preclude the need for glue or screws though...

The LED is fixed to the star with solder, so that shouldnt be a problem. Wink

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NightCrawl wrote:

dthrckt wrote:
I’ve been planning to. but, I don’t think it has better heat transfer than well lapped parts http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/ it does preclude the need for glue or screws though…

The LED is fixed to the star with solder, so that shouldnt be a problem. Wink

not sure what you mean.

adding another layer of solder (low thermal conductivity vs aluminum, copper and brass) isn’t going to improve anything

there are real world tests of the two configs (mated parts vs soldered parts) that can be found with google…

anyway, if you have a brass pill, skip the pcb and solder the led to the pill…

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How do you lap the inside of the pill where the base of the star will sit? Usually they have a rim around the flat surface, please explain what tools do you use to lap it.

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screwing the pill down is a very good way to do it. but if you have never drilled and tapped a hole i suggest you buy multiple drill bits and multiple taps and practice on similair material before you attempt working on that emitter pill. working with such small drills and taps such as 2-56 or 4-40 requires a learning curve Wink

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i cant suggest whats the best. but optimum conditions using a thermal compound is having both the mating surfaces as smooth and flat as possible. you also want as little thermal compound between those surfaces as possible. the purpose of thermal compounds is to fill in the microscopic pores and scratches. if possible, compressing the parts together to get as much unneeded compound squeezed out from between them possible would be great too

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I unsolder the emitter, take a steel punch that has a flat face, set it on the pcb and hot glue it in place. sometimes I use a cordless drill to spin it slowly, some times I do it entirely by hand (takes awhile).

I use 600 grit lapping compound and then alumina, i forget the micron size but it is equivalent to 1200 grit (mixed with water or mineral oil).

like matt mentioned – it makes it difficult to solder leads to the pcb because the heat transfer is so much better. I just prop the edge up a bit w/ something in order to solder

here is how much contact a typical stock pcb has (the dark portion only)

eventually, the whole thing is dark. I scrub with a toothbrush afterwards to get alumina out. then wipe thermal grease onto is as thin as possible.

and as you can see, I just watch a movie while doing it, so it doesn’t feel like a big waste of time Smile

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I don’t work much with torches (mostly bike lights) so I couldn’t really tell you, but for lapping flat surfaces and stars I use 400>800>1000>1500>2000>Mothers Mag polish with plenty of water/ spit on the wet’n‘dry, using the flat on my vise as a flat surface. You can easily feel the difference with your finger tip afterwards Smile

To do a pill, I would probably get some wood dowel 1/2 to 1/4 the diameter of the pill and wrap the sandpaper over the end. It’ll be fiddly, but with some patience you should be able to get it smoother at least.

I would really caution using screws with small stars as the screw heads can easily interfere with the optic or reflector. I’ve never had problems with 20mm stars, but the one 16mm star I used in a recent build was a complete bear. Get the smallest flattest screws you can find if you’re going that route!

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to be clear, I mate the pill and pcb when lapping, I don’t just flatten them. though judging from the pcbs I’ve lapped, even just flattening them would be a significant improvement.

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dthrckt wrote:
NightCrawl wrote:

dthrckt wrote:
I've been planning to. but, I don't think it has better heat transfer than well lapped parts http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/ it does preclude the need for glue or screws though...

The LED is fixed to the star with solder, so that shouldnt be a problem. Wink

not sure what you mean. adding another layer of solder (low thermal conductivity vs aluminum, copper and brass) isn't going to improve anything there are real world tests of the two configs (mated parts vs soldered parts) that can be found with google... anyway, if you have a brass pill, skip the pcb and solder the led to the pill...

If you have a copper pcb and a brass pill, soldering those together is superior to almost anything except for extremly tight lapped surfaces.. there is already a solder connection between the heat source (=LED) and the heatsink (=PCB), so adding another one to connect the PCB to a larger heatsink cant have a negative influence. On cpf I read that someone grinded down the bottom of emitters and glued them on with something really good.. I mean there is stuff with better thermal conductivity than aluminium, its just very expensive. I think it was linked in the "lets discuss heatsinking" thread.

But yes, stock PCBs have very poor connection because they are so uneven.

For P60 pills: I wouldnt mind removing the rim, havent noticed any negative effects so far.

As for lapping: I find it easier to flatten pcb and heatsink first with sandpaper and bring them to a mirror-like finish, going up to 2500 grid. Then some lapping and you are done, although its better to be good at sanding than to be bad at lapping. Wink

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Nice tips, guys. I usually use 000/0000 steel wool followed by Brasso or Mother’s until both the PCB and heatsink shine.

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like I said, well lapped is superior.

soldering them together DOES have a negative influence vs lapped….it adds an additional layer of metal that has a lower thermal conductivity…

there is stuff w/ better thermal conductivity than aluminum, but it sure isn’t solder.

would soldering be better than unlapped pcb with thermal paste. sure, unless you use way too much solder.

now, with a copper pcb, that likely has a gold coating to resist tarnish, solder might be wiser than lapping in the long term, since you’d remove the gold when lapping…

have you ever lapped a pcb? try it Smile

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Of course, the whole discussion is sort of a mute point. Real world, single emitter lights don't have to go to extremes, just clean the surfaces and apply whatever you want, either thermal compound or thermal adhesive and give it some pressure. Good enough for 95% of the lights out there and only a highly modded "hot light", would really need the extra attention.

Even with those, most of us would use it a few times, for short periond and then put it on the shelf, sell it, trade it, or give it away, so in 99% of the cases, it's not really a big issue, it's just an issue in our minds.

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Old-Lumens wrote:

Of course, the whole discussion is sort of a mute point. Real world, single emitter lights don’t have to go to extremes, just clean the surfaces and apply whatever you want, either thermal compound or thermal adhesive and give it some pressure. Good enough for 95% of the lights out there and only a highly modded “hot light”, would really need the extra attention.

Even with those, most of us would use it a few times, for short periond and then put it on the shelf, sell it, trade it, or give it away, so in 99% of the cases, it’s not really a big issue, it’s just an issue in our minds.

yup

mating parts by lapping takes too long to ever be used in production, or by people that aren’t as silly as I am. soldering would takes seconds…

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