Whats the best thermal compound?

[dthrckt]

@Old-Lumens

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…

[Kokopelli]

I always wondered how good a baby soothing creme with zinc oxide would work as a heatsink grease. They look and feel like thick thermal greases.

[dthrckt]

was it viffer that tested toothpaste?

i think the best thermal grease is the one you have on hand, and apply properly

[ChimpOnABike]

I dunno, a lot of the performance CPU heatsinks out there are pretty much lapped out of the box. If you automate the process the time overhead is really fairly small. Coming from a computing background I’m surprised just how badly heat is managed in flashlights, the amount of thermal gunk in my bike lights suggests that they never read the instructions as it’s far to thick to be effective.

[ChimpOnABike]

@dthrckt

was it viffer that tested toothpaste?

i think the best thermal grease is the one you have on hand, and apply properly

You really want to avoid getting thermal paste on your skin. The AS stuff can be quite toxic and is a bugger to remove as it really gets into the pores.

[dthrckt]

didn’t know it is toxic!

but certainly found out it is a bugger to get off of just about anything.

I use a credit card (or similar piece of flat edge plastic) to scrape off excess, and acetone to clean up.

[mattthemuppet]

@Old-Lumens

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.

hah! But if we weren’t OCD, we’d just buy a Craftsman LED torch from Walmart and be happy with it, wouldn’t we

I’d wager that most of the single emitter lights on here would benefit greatly from better thermal management, given how much heat they’re producing in such a small place. You only have to look at the output drop from switch on to +15min to see how ineffective they are at dissipating heat. I’m not saying cleaning up just one thermal interface (between star and pill) is going to magically solve that problem, but it’ll help.

[gords1001]

All this has really got me thinking about the Jacob a60 and ke-5 I just nodded, on both I sanded then wire wooled the anodizing off and polished the stars, now perhaps, I should go further next time.

I’m also thinking I need to get an hd2010 to play with…

[dthrckt]

you sanded off the anodizing from the outside?!

[texaspyro]

@ChimpOnABike

The AS stuff can be quite toxic

Check their MSDS (material safety data sheet)… it’s rather benign. Don’t spread it on crackers, though.

[texaspyro]

Pretty much all thermal compounds perform the same! The main difference between a good and poor compound is the long term stability of the carrier fluid used to make up the paste.

[Bort]

Lots of interesting info in this thread, for my application i want to replace the star in this photo

with this in xm-l2 when it becomes available

So i want the best thermal transfer compound made by man, economically achievable

[gords1001]

@dthrckt

you sanded off the anodizing from the outside?!

Sorry, I’m thinking everyone knows what I’m on about, on both the Jacobs and the ke-5, there is no pill, the light engine is part of the host, as such, its anodized just like the rest of the host, so I sanded and polished under where the star will sit, so the star was pasted direct to the host alu, rather than there being an anodized layer between the base of the star and the aluminium of the light engine, now I see, I should have also polished the base of the star flat too, something I’ve wondered about.

[dthrckt]

if you’re not willing to drill a couple holes and screw it down then you’ll need an adhesive one

Arctic Silver Arctic Alumina 5g Thermal Adhesive Set AATA-5G - Newegg.com

slightly cheaper on ebay or walmart, but i like newegg

[NightCrawl]

@dthrckt

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

Lapped might be superior when done professional. With home tools? I'm unsure..

How could soldering have any negative effect? You already have a layer of solder between LED and PCB, but the layer between PCB and heatsink would have 10times the area -> better heat conduction. If you have a 1" pipe at the source it doesnt matter how many 1" pipes you add in the path, even if some are 3"..

Actually aluminium PCBs would be great if you could solder the LED directly on the aluminium, without the dielectric layer and all that stuff inbetween. Thats the main advantage of copper pcbs. I think even brass PCBs would be better if its a good alloy.

And I dont think the gold layer has any influence on thermal conductivity at all. Its there so the copper doesnt oxidate. Also, even those copper PCBs from LED-tech are uneven because they are punched out..

@ChimpOnABike: CPU heatsinks arent lapped because you need both parts for lapping. They are sometimes sanded pretty good, but often far from a mirror-like finish. Its an easy improvement actually.

[texaspyro]

@Bort

So i want the best thermal transfer compound made by man, economically achievable

Something with powdered diamond in it. Diamond powder is actually not too expensive. Check Ebay:
Shop by Category | eBay%28dust%2Cpowder%29&_sacat=3213&_odkw=diamond%28dust%2Cpowder%29+mesh&_sac=1&_osacat=3213&_from=R40

[Rezolution]

@texaspyro

@Bort

So i want the best thermal transfer compound made by man, economically achievable

Something with powdered diamond in it. Diamond powder is actually not too expensive. Check Ebay:
Shop by Category | eBay%28dust%2Cpowder%29&_sacat=3213&_odkw=diamond%28dust%2Cpowder%29+mesh&_sac=1&_osacat=3213&_from=R40

If you’re looking for diamond based paste: Amazon.com

[dthrckt]

@gords1001

@dthrckt

you sanded off the anodizing from the outside?!

Sorry, I’m thinking everyone knows what I’m on about, on both the Jacobs and the ke-5, there is no pill, the light engine is part of the host, as such, its anodized just like the rest of the host, so I sanded and polished under where the star will sit, so the star was pasted direct to the host alu, rather than there being an anodized layer between the base of the star and the aluminium of the light engine, now I see, I should have also polished the base of the star flat too, something I’ve wondered about.

ah, yes, I dont’ own either.

probably a good idea to remove.

I’ll be using some mother’s polish as a last step next time I do a pcb…

[dthrckt]

@NightCrawl

Lapped might be superior when done professional.

well, I have lapped machined parts professionally, but I don’t think someone else needs to have been paid to do a good job. it does take some patience.

@NightCrawl

How could soldering have any negative effect? You already have a layer of solder between LED and PCB, but the layer between PCB and heatsink would have 10times the area -> better heat conduction. If you have a 1” pipe at the source it doesnt matter how many 1” pipes you add in the path, even if some are 3”…

there isn’t any fluid mechanics involved here, so fluid in pipes isn’t a good analogy.
i’m not sure how to explain it differently. Maybe we’ll have to agree to disagree.
the thermal conductivity of solder is lower than the metals involved, so putting it in between them reduces thermal conductivity if they have very good contact before soldering - what happens before or after that can change the temperature gradient in operation, but not the properties of the materials at the junction.
I guess we’ll have to agree disagree.

@NightCrawl

Actually aluminium PCBs would be great if you could solder the LED directly on the aluminium, without the dielectric layer and all that stuff inbetween. Thats the main advantage of copper pcbs. I think even brass PCBs would be better if its a good alloy.

you can solder aluminum, but it requires a different solder, or at least a different flux, and it is a PITA

@NightCrawl

And I dont think the gold layer has any influence on thermal conductivity at all. Its there so the copper doesnt oxidate.

any material will have ‘some’ influence but it’d be near impossible to measure
anyway, I didn’t mean to imply that’s why gold shouldn’t be removed…I meant you don’t want the copper to tarnish…which would surely reduce contact area as well as thermal conductivity…

anyway, let me know when you find copper PCBs, I’d be happy to test this scenario.

[NightCrawl]

@dthrckt

well, I have lapped machined parts professionally, but I don’t think someone else needs to have been paid to do a good job. it does take some patience.

I meant with the proper tools, not necessarily paying someone to do that..

@dthrckt

there isn’t any fluid mechanics involved here, so fluid in pipes isn’t a good analogy. i’m not sure how to explain it differently. Maybe we’ll have to agree to disagree. the thermal conductivity of solder is lower than the metals involved, so putting it in between them reduces thermal conductivity if they have very good contact before soldering - what happens before or after that can change the temperature gradient in operation, but not the properties of the materials at the junction. I guess we’ll have to agree disagree.

Its the easiest I could think of.. I'm not good at calculating, but as there already is solder involved right under the LED, it cant really get worse. Maybe someone who knows how to calculate that stuff can chime in..

Metal to metal is of course superior, but if someone doesnt have the tools or patience, soldering is as good as he can get. Agreed? :D

@dthrckt

you can solder aluminum, but it requires a different solder, or at least a different flux, and it is a PITA

I know, I did it before.. but as you said, not easy and therefore (I guess) rather expensive to produce. So they dont..

@dthrckt

any material will have ‘some’ influence but it’d be near impossible to measure anyway, I didn’t mean to imply that’s why gold shouldn’t be removed…I meant you don’t want the copper to tarnish…which would surely reduce contact area as well as thermal conductivity… anyway, let me know when you find copper PCBs, I’d be happy to test this scenario.

Well, gold is worse than copper, so.. :P

And yes, its there so the copper wont tarnish and its easier to solder to. But if you plan on using the copper stars from LED-tech, you better sand them, because they arent much better (regarding how even they are) than all those aluminium stars.