Whats the best thermal compound?

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Kokopelli
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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
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was it viffer that tested toothpaste?

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

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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.

Don’t be a chump, be a chimp!

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dthrckt wrote:
was it viffer that tested toothpaste?

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

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.

Don’t be a chump, be a chimp!

dthrckt
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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
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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.

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 Smile

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
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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
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you sanded off the anodizing from the outside?!

texaspyro
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ChimpOnABike wrote:
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
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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
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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

The Journal of Alternative Facts

"It is critical that there is a credible academic source for the growing and important discipline of Alternative Facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists."

 

gords1001
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dthrckt wrote:
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
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if you’re not willing to drill a couple holes and screw it down then you’ll need an adhesive one

http://www.newegg.com/Product/Product.aspx?Item=N82E16835100013

slightly cheaper on ebay or walmart, but i like newegg

NightCrawl
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dthrckt wrote:
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
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Bort wrote:
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:
http://www.ebay.com/sch/i.html?_nkw=diamond+%28dust%2Cpowder%29&_sacat=3...

Rezolution
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texaspyro wrote:
Bort wrote:
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:
http://www.ebay.com/sch/i.html?_nkw=diamond+%28dust%2Cpowder%29&_sacat=3...

If you’re looking for diamond based paste: http://www.amazon.com/Innovation-Cooling-Diamond-Thermal-Compound/dp/B00...

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gords1001 wrote:
dthrckt wrote:
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…

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NightCrawl wrote:
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 wrote:

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 wrote:
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 wrote:
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.

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dthrckt wrote:
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 wrote:
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? Big Smile

dthrckt wrote:
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 wrote:
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.. Silly

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.

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You guys gave me an idea on how to lap the insides of the pill very flat

I currently lap my stars on a flat piece of glass using wet/dry sandpaper progresively up to 2000 grit.

For the pill I am thinking on using a steel bolt like this

And lap the bolt’s head flat on a glass using wet / dry sandpaper up to 2000 grit and then glue wet / dry sandpaper to the bolt’s head and lap the inside of the pill up to 2000 grit using a drill, IMHO it should produce really good results, what do you guys think?

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NightCrawl wrote:
Maybe someone who knows how to calculate that stuff can chime in..

I’m familiar with the calculations, although admittedly not as familiar as when I passed thermodynamics w/ an A grade 16 years ago

The problem with calculating this is, interfacial thermal resistance is empirical.

I like this stuff, so I spent a couple hours last night looking for test data. ( No mystery why I’m single Silly )

I couldn’t find a study of ‘copper to copper’ vs ‘copper to solder’ interfaces. The closest I could find, in different studies, was that a milled copper to copper interface (1.6um roughness…not lapped), with no thermal compound, is has an order of magnitude lower thermal conductance than a copper-solder-copper sandwich where the solder is <30um thick and has above average (for solder) thermal conductivity. Of note, a copper-copper interface that is ground (3.6um) is 3x worse than milled…

So…I find that data interesting, and pointing in the direction of solder being superior…but ultimately inconclusive…

NightCrawl wrote:
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? Big Smile

If you’re good at soldering Silly

I definitely think soldering is easier – although it doesn’t preclude lapping…in fact the copper solder sandwich study used lapped copper discs….

I picked up a good tip from that study. calculate the amount required to cover the contact area with 10um layer, use a little excess, press the parts together while still hot to squeeze out excess.

anyway, maybe some day we’ll get to test this. unfortunately, the studies I found use a laser for heating and very accurate measuring equipment…which to me implies, even if we get the chance to test, we’d be hard pressed to tell the difference w/ ‘amateur’ test equipment :bigsmile:

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Bort wrote:
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

Lets recap, I was hoping for some consensus or side by side testing, but so far it seems to be a contest between

http://www.frys.com/product/6274350
http://www.intl-outdoor.com/shinetsu-x237783d-thermal-grease-5-pcs-p-480...
same product, different numbers

http://img.photobucket.com/albums/v722/Duane_Bolt/tim.jpg

http://www.wakefield.com/Catalog/tabid/92/CategoryID/110/ProductID/362/D...

http://vendor.parker.com/Groups/Seal/Divisions/Chomerics/Chomerics%20Product%20Library.nsf/24eb4985905ece34852569580074557a/c72bd4ba4470f5ff852570ce006d53a0/$FILE/Thermal%20Grease%20T650-T660.pdf

and

http://www.amazon.com/Innovation-Cooling-Diamond-Thermal-Compound/dp/B00...

finally, according to this don’t use cheese
http://www.techjamaica.com/forums/showthread.php?73392-Thermal-Paste-Sho...!

Also a suggestion to use as little compound as possible just to fill in air gaps (if the compound is more conductive then the metals then this advice may be mute?)
Can somebody wade through these and figure out the best 3?

The Journal of Alternative Facts

"It is critical that there is a credible academic source for the growing and important discipline of Alternative Facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists."

 

dthrckt
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sorry for distracting your thread 0:)

yes as far as use as little compound as possible, the compound will not be superior to metal.

if you’re not going to screw down the PCB, then you will need adhesive compound.

the technique (or at least my technique) is different for adhesive compound.

Since I flatten/lap the surface, I apply grease-like compound to both surfaces, rub it in to eliminate air, then scrape it off with something flat.

For adhesive, I apply to both surfaces, rub it in, then clamp the two parts together, so that excess squeezes out, and pressure is maintained while the adhesive sets.

i’ll look at the links then reply more Beer

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the last two links did work for me

the first two links are not adhesive.

the only adhesive thermal compounds I’m familiar with are fujik and arctic silver adhesive.

Start at the top of the chart you linked, search the product name (ie the products that don’t say they’re a grease) and when you find one that’s adhesive, and above arctic silver adhesive in the chart…you’ve got your answer Smile

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dthrckt wrote:
the last two links did work for me

the first two links are not adhesive.

the only adhesive thermal compounds I’m familiar with are fujik and arctic silver adhesive.

Start at the top of the chart you linked, search the product name (ie the products that don’t say they’re a grease) and when you find one that’s adhesive, and above arctic silver adhesive in the chart…you’ve got your answer Smile


adhesive is not necessary, just superior thermal transfer

The Journal of Alternative Facts

"It is critical that there is a credible academic source for the growing and important discipline of Alternative Facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists."

 

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dthrckt wrote:
I'm familiar with the calculations, although admittedly not as familiar as when I passed thermodynamics w/ an A grade _16 years ago_... The problem with calculating this is, interfacial thermal resistance is empirical. I like this stuff, so I spent a couple hours last night looking for test data. ( No mystery why I'm single Silly ) I couldn't find a study of 'copper to copper' vs 'copper to solder' interfaces. The closest I could find, in different studies, was that a milled copper to copper interface (1.6um roughness...not lapped), with no thermal compound, is has an order of magnitude lower thermal conductance than a copper-solder-copper sandwich where the solder is <30um thick and has above average (for solder) thermal conductivity. Of note, a copper-copper interface that is ground (3.6um) is 3x worse than milled... So...I find that data interesting, and pointing in the +direction of solder being superior+...but ultimately inconclusive...

Awwww..^^

So.. if grounding (=sanding?) isnt that good, would lapping be between sanding and milling then?

Oh and I read somewhere that the thickness of solder wouldnt really matter.. I dont really know about that.

Well, for the regular home-modder soldering is a good choice if copper pcbs are available.. and some soldering skills. Big Smile

dthrckt wrote:
If you're good at soldering Silly I definitely think soldering is easier - although it doesn't preclude lapping...in fact the copper solder sandwich study used lapped copper discs.... I picked up a good tip from that study. calculate the amount required to cover the contact area with 10um layer, use a little excess, press the parts together while still hot to squeeze out excess. anyway, maybe some day we'll get to test this. unfortunately, the studies I found use a laser for heating and very accurate measuring equipment...which to me implies, even if we get the chance to test, we'd be hard pressed to tell the difference w/ 'amateur' test equipment :bigsmile:

Yup, some soldering skills might be helpful anyways for modding. Big Smile

But I think its great that we have found a point where we might lack test equipment to see whats better for home users.. not too bad IMO.

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texaspyro wrote:
ChimpOnABike wrote:
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.

It depends on which compound you use as some are worse than others. Anything with high levels of silver and given enough of it you run the risk of Argyria, although I totally accept this is low risk unless you’re using it on a daily basis. I can’t find the link (it was back in my PC modding days several years back) but I have seen dermatology people talk about problems with the very fine particle size and skin reactions. Either way it’s best not to eat it or get it on skin, although you won’t drop dead on the spot if you do.

Don’t be a chump, be a chimp!

dthrckt
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NightCrawl wrote:
So.. if grounding (=sanding?) isnt that good, would lapping be between sanding and milling then?

Oh and I read somewhere that the thickness of solder wouldnt really matter.. I dont really know about that.

after some searching…
mirror polish aluminum surface roughness approaches .0005 um.
amateur polishing is more like .4 um

the copper-solder-copper study found a ~20% improvement in thermal interface conductance by reducing solder layer from 30um to 10um.

NightCrawl wrote:
But I think its great that we have found a point where we might lack test equipment to see whats better for home users.. not too bad IMO

absolutely.

hot rodding flashlights! pun intended Wink

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Anyone tried to use the “liquid metalpad” for LED mounting?
Its a thin foil of some metal mixture that has a melting point of (iirc) 60 degrees celsius,
and usually you put it between CPU and heatsink and then drive the CPU until the stuff melts.
Somewhere i saw a comparison chart of different thermal “greases” and this one had the lowest thermal bulk resistance.

Now using that + lapping both the copper MCPCB and the heatsink to also reduce the interface resistance
seems to me like a very good way of keeping the LED cool.

And regarding solder: how good is the thermal conductivity of silver solder? (googling around i found that
you use this to hard-solder copper pieces, and it is more than 60% copper and silver, which conducts heat even better
than copper)
It probably can’t be used do mount MCPCB to heatsink because it takes too much heat to solder, which the led wouldn’t survive.
But reading around in the forums i learned that some people actually build their own copper heatsinks without a lathe,
by hard-soldering flat sheets of copper together. With this kind of solder, the resulting heatsink should be close to pure copper, right?

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Not really. Copper is around 350W/m.K while even silver solder is below 100W/m.K IIRC. Still far better than most heatsinks tho.


And those metal pads.. they are very expensive right?

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