# Thermal compounds



## BIGWOOD (Nov 29, 2012)

I'm currently using Fujik Silicone Thermal Glue but I heard that there are better stuff out on the market for transferring heat from the LED to the heatsink like the Arctic Silver products. Is this true and someone tested? And what about potting the driver? What would you use is this case? I took a look at their website and there are quite a few different products. Now I'm confused as to which one would be the best for different applications.

1. Arctic Silver 5
2. Céramique 2
3. Arctic Alumina

and then there are the adhesives & epoxies...:thinking: Any suggestions would be much appreciated.


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## ma_sha1 (Nov 29, 2012)

Arctic Silver 5 is not a glue, I use it for inserting heat sink to flashlight body, so it's removable.

The two parts Arctic Silver is excellent thermo glue, better than Fujik or Arctic Alumina, I use it for glue down led star

Fujik is non conductive, I use it for potting drivers.

I don't know Céramique 2, never used it.


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## BIGWOOD (Nov 29, 2012)

ma_sha1,

Thanks for the clear explanation.


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## The_Driver (Nov 29, 2012)

DIEMAT DM6030Hk is much better than anything listed above (see the table of page 2 of the datasheet I linked too). It even noticeably better than soldering an emitter directly to a copper heatsink which is generally regarded as the best thing one can do to improve heat transfer. 
Saabluster uses it for most of his lights (look at this post of his and also this one). 
Unfortunately the minimum order amount of 50g costs $350...  (you also need an oven)


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## BIGWOOD (Nov 29, 2012)

WOW - That's quite an eye opener in terms of how far some of the members go to improve heat transfer. Thanks for sharing.

For my purposes it's a little too hardcore for me and not to mention out of my price range. I rather swap out the $5 LED for a new one once it burns out.


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## CTS (Nov 29, 2012)

The_Driver said:


> DIEMAT DM6030Hk is much better than anything listed above (see the table of page 2 of the datasheet I linked too). It even noticeably better than soldering an emitter directly to a copper heatsink which is generally regarded as the best thing one can do to improve heat transfer.
> Saabluster uses it for most of his lights (look at this post of his and also this one).
> Unfortunately the minimum order amount of 50g costs $350...  (you also need an oven)



I suppose it's somewhat ironic that while I was writing a post about thermal issues this post appeared.

You must be very cautious about spec sheets. These look an awful lot like scientific documents but don't think for a moment these get out the door without the marketing department getting their fingerprints on them.

I read a study a while back done by a university, sponsored by ASME, that addressed thermal adhesive conductivity. In that test the high silver filled adhesives outperformed other materials by a margin of 10 to 1. That was at an application thickness of approx 1/2 millimeter. At the absolute minimum thickness they could bond the surfaces the least expensive, most low-tech material was a couple percentage points better than the hyper-expensive high silver content epoxy. I believe that material was a filled RTV silicone. I will try to look for the document.

Their rating of 60 w/m K is right around the transfer ability of silver solder. Tin/silver solder is about 20 points higher, just a tick shy of indium.

In this context, keep in mind that solder isn't affected by the bond thickness. It conducts the same amount of heat per given area regardless of how thick it is (within reason- at some point you have the resistance issue). If one were to use a compound such as Diemat, they would be faced with the challenge of positioning the diode, then pressing it to achieve an adhesive thickness of 0.005"


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## The_Driver (Nov 30, 2012)

CTS said:


> I suppose it's somewhat ironic that while I was writing a post about thermal issues this post appeared.
> 
> You must be very cautious about spec sheets. These look an awful lot like scientific documents but don't think for a moment these get out the door without the marketing department getting their fingerprints on them.
> 
> ...



Thanks for the insight, I never thought about it that way. I remember saabluster mentionining somewhere that he also uses it because it is easier to epoxy emitters with this stuff than directly soldering onto the copper heatsinks. I'm guessing it's easier because the emitter doesn't float around (requiring re-centering it) like it does when being soldered...

It would be nice if he would give some insight on this topic. He must have very good reasons for using this super expensive stuff...


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## CTS (Nov 30, 2012)

I just posted some math about the various interfaces in the thermal path in the other thread I started. In looking at what's below the diode, I don't know if doing anything more than using the MCPCB gets you anything. Your off-the-shelf MCPCB is capable of conducting twice the heat generated by the LED. What I mean is twice the heat that the LED is able to thermally conduct through an ideal bond of about 60 w/m K. If you used that 60 bond at 4 sq/mm to bond it to a solid diamond heat sink at 2000W/m K you're still only going to conduct as much heat as the diode joint can carry. To do much better, either the surface area of the diode needs to increase or the bond needs to be improved at the manufacturer level. I have no idea how diodes are made or what the die material is. But if you assumed for a moment that it's a piece of copper, the die could be furnace brazed to a copper board before assembly- or a single piece base. 

I'm going to go out on a limb and do some theorizing. If what I'm noticing is true, manufacturers are looking for increases in efficiency and output. If they were able to get vastly increased output by simply making the thermal conductive abilities of the diode more efficient, they would be doing just that. My guess is that the diode itself is the limiting factor- that even if you had 100% thermal conductance from the die, the LED's internal ability to conduct heat to the die is limited.

I would definitely like to learn more.


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## The_Driver (Nov 30, 2012)

CTS said:


> I just posted some math about the various interfaces in the thermal path in the other thread I started. In looking at what's below the diode, I don't know if doing anything more than using the MCPCB gets you anything. Your off-the-shelf MCPCB is capable of conducting twice the heat generated by the LED. What I mean is twice the heat that the LED is able to thermally conduct through an ideal bond of about 60 w/m K. If you used that 60 bond at 4 sq/mm to bond it to a solid diamond heat sink at 2000W/m K you're still only going to conduct as much heat as the diode joint can carry. To do much better, either the surface area of the diode needs to increase or the bond needs to be improved at the manufacturer level. I have no idea how diodes are made or what the die material is. But if you assumed for a moment that it's a piece of copper, the die could be furnace brazed to a copper board before assembly- or a single piece base.
> 
> I'm going to go out on a limb and do some theorizing. If what I'm noticing is true, manufacturers are looking for increases in efficiency and output. If they were able to get vastly increased output by simply making the thermal conductive abilities of the diode more efficient, they would be doing just that. My guess is that the diode itself is the limiting factor- that even if you had 100% thermal conductance from the die, the LED's internal ability to conduct heat to the die is limited.
> 
> I would definitely like to learn more.



Have you seen this thread: Why a good thermal path really matters?


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## CTS (Nov 30, 2012)

The_Driver said:


> Have you seen this thread: Why a good thermal path really matters?



Took a look thru just now. What strikes me is the speed at which these devices are developing. It also serves to illustrate a point that a neophyte like me probably could overlook, yet an experienced builder just assumes- that while most of these products look alike, there are broad variances in quality.

Over the last several years my industry has been permeated with some truly abhorrent Chinese made $h... I have gained an almost reflexive disdain for anything made there, since I have to sometimes live with the results. It makes me wonder just how many new hobbyists are pushed away from this segment of the hobby thinking that it's just too hard when their issues actually stem from lesser quality components. Many are drawn to the appeal of that stunner light that's small yet delivers amazing amounts of light, yet they end up with something that breaks easily and often from something as simple as using a $2 board instead of a $4 piece, not appreciating the differences. This was one of my first thoughts when seeing people reflowing diodes and not discussing the solder formulation. How many people think there are just two kinds of solders- electrical and plumbing?

Thanks for the link- It'll be a good read this evening


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## The_Driver (Nov 30, 2012)

CTS said:


> Took a look thru just now. What strikes me is the speed at which these devices are developing. It also serves to illustrate a point that a neophyte like me probably could overlook, yet an experienced builder just assumes- that while most of these products look alike, there are broad variances in quality.
> 
> Over the last several years my industry has been permeated with some truly abhorrent Chinese made $h... I have gained an almost reflexive disdain for anything made there, since I have to sometimes live with the results. It makes me wonder just how many new hobbyists are pushed away from this segment of the hobby thinking that it's just too hard when their issues actually stem from lesser quality components. Many are drawn to the appeal of that stunner light that's small yet delivers amazing amounts of light, yet they end up with something that breaks easily and often from something as simple as using a $2 board instead of a $4 piece, not appreciating the differences. This was one of my first thoughts when seeing people reflowing diodes and not discussing the solder formulation. How many people think there are just two kinds of solders- electrical and plumbing?
> 
> Thanks for the link- It'll be a good read this evening



Well...
The led to copper bonding/soldering thing is only done by a select few modders here. No flashlight manufacturer does this. 
You always have to think about if all these improvements actually make a practical difference. If a normal flashlight is 7% brighter because of very expensive heatsinking techniques than those aren't really worth it.
When leds are driven at moderate current levels they never get thaaat hot in the first place. A PCB thermal-epoxied to a reasonably sized aluminum heatsink will do fine. 
A DEFT from saabluster (Cree XR-E overdriven at 1.5A-1.7A) or the Varapower lights are totally different beasts.


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## CTS (Nov 30, 2012)

I very much agree. We're talking about pushing these devices well beyond their design specs. That's the fun part!


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## Hoop (Dec 3, 2012)

Some of the luminus chips such as the CST-90 and CSM-360 etc. are, I believe, directly formed upon their copper PCB's and it greatly helps with heat transfer. Also, the led-tech.de copper PCB's are well regarded as far as XML stars go.

Check out the Skinnee Labs thermal compound roundup for a comparison of pc related performance of common thermal pastes.


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## The_Driver (Dec 3, 2012)

Hoop said:


> Some of the luminus chips such as the CST-90 and CSM-360 etc. are, I believe, directly formed upon their copper PCB's and it greatly helps with heat transfer. Also, the led-tech.de copper PCB's are well regarded as far as XML stars go.
> 
> 
> Check out the Skinnee Labs thermal compound roundup for a comparison of pc related performance of common thermal pastes.



The luminus chips with are factory mounted on copper pcbs aren't any better than a loose one soldered to a copper heatsink. They are made for projectors, where they are driven hard, but the manufacturing needs to be efficient and easy. It's easier to screw a package like this (which also has a socket for a special plug on the pcb) into a projector and just connect the plug instead of doing everything by hand or having a reflow soldering machine do it.

The Indigo Extreme which is the best solution in that thermal "paste" comparison is rated at 20W/m K


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## bshanahan14rulz (Dec 3, 2012)

uh-oh.


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## Hoop (Dec 3, 2012)

The_Driver said:


> The luminus chips with are factory mounted on copper pcbs aren't any better than a loose one soldered to a copper heatsink. They are made for projectors, where they are driven hard, but the manufacturing needs to be efficient and easy. It's easier to screw a package like this (which also has a socket for a special plug on the pcb) into a projector and just connect the plug instead of doing everything by hand or having a reflow soldering machine do it.



The copper luminus chips have a thermal resistance of .92*C/W and the loose SST-90 is at .64*C/W. With a thin solder layer I see what you mean; you would beat the copper offering. Compared to a loose XML which has 2.5*C/W, the copper luminus chips look pretty nice though. 



The_Driver said:


> The Indigo Extreme which is the best solution in that thermal "paste" comparison is rated at 20W/m K



Indigo Extreme is not a thermal paste, but rather a engineered thermal interface. It is a metal pad which needs to melt and cure. Interesting is that the thermal pastes come close to its performance in those tests when the best thermal paste, Prolimatech PK-1, has a thermal conductivity of 10.2 W/m-℃.


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## The_Driver (Dec 4, 2012)

Hoop said:


> Indigo Extreme is not a thermal paste, but rather a engineered thermal interface. It is a metal pad which needs to melt and cure. Interesting is that the thermal pastes come close to its performance in those tests when the best thermal paste, Prolimatech PK-1, has a thermal conductivity of 10.2 W/m-℃.



I know . 
Thats why I put the word paste in apostrophes.


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## CTS (Dec 5, 2012)

I looked at Indigo. I suspected by your reference to it melting that it was a phase-change alloy. It's a great concept but has limitations, one of which pretty much negates its use with LED's. PCA's are very reactive to oxygen. They are only useful in an application where air/water can be sealed out. There's a significant difference in scale- 1600 sq/mm on the CPU vs 7-9 sq/mm with an LED. On a computer CPU, there's plenty of room around the outside for gasketing. If you look at the products offered you'll see that in their packaging. Gallium is another fantastic thermal conductor. It has the advantage of being a liquid at room temperature so it's very easy to use. Unfortunately it gobbles up aluminum like a leaking alkaline battery.

There are some things that are for the most part are carved in stone. Metals conduct heat better than just about anything else. Heat transfers at the atomic level, so metal atoms bonded at the atomic level will conduct heat better than metals touching each other. If you took two copper blocks, one cast and one made of sintered copper particles, the copper block will conduct better. Simple physics. In a real world application, it's not a miracle material that provides the solution. It's going to be an understanding of all the issues and attending to every detail. A copper PCB does nothing for you if it has a lousy contact area with the bottom of the diode. There are no materials that will affix a diode with better thermal conductivity than several readily=available solders. On the flipside, you can cause yourself problems by ignoring that there are dramatic differences in conductivity across the range of solder alloys. Understanding that bond thickness is critically important can have dramatic effects.

On Indigo, before I went to all that trouble of sealing it (and I suspect the pricetag of some gee-whiz consumer product) I'd look at one of the high-conductivity adhesives. Diemat, which I have no experience with, is purported to conduct at 60.

The point I'm trying to make is that to build a high-performance design, you have to have a handle on all the variables and that requires quantifying exactly what conductive values you have at each point.

If your goal is to get triple SST-90's in a stock Mag D head and not glue the boards to the sink, you have design limitations- barriers put into place by the laws of physics. Now if you've got a Peltier cooler and an exhaust fan in the tailcap, you're probably getting closer to something that works.


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## thijsco19 (Dec 5, 2012)

I have a small question, does anodisation effect the heat transfer between alluminium?


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## CTS (Dec 5, 2012)

thijsco19 said:


> I have a small question, does anodisation effect the heat transfer between alluminium?



Anodizing is an exceptional medium for heat emission. That's where that conductive heat energy is radiated out in the form of magnetic radiation (radiant heat). Most heat sinks are made from aluminum and anodized for this very reason. There are specialty coatings out there used as heat disbursing agents that are based on alumina, which is the ceramic that is formed when the aluminum is anodized. 

For conduction, it has, depending on thickness a substantial insulating effect. I've read that it cuts conductivity between ten and thirty times.

The short- great on the outside, bad on the inside.


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## thijsco19 (Dec 6, 2012)

So I have to remove the inner anodizing layer for the best heat transfer between the heatsink and the body, I will use some thermal compound (some basic pc stuff) between it.

What's the best methode to remove a anodization layer?


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## CTS (Dec 6, 2012)

The best method to remove the anodizing is a carbide cutter on the end of a boring bar. It's pretty tough. 

If you don't have a lathe, you're down to sanding it out. Oven cleaner will work on decorative anodizing but doesn't really touch hard anodizing. Plus you risk ruining the exterior that you want to keep.

If you can find one, get one of those expanding rubber cylinder arbors that sanding sleeves slip over. Mount it in a drill press and run it up and down. Those arbors usually have short shanks. I have an extension that I made out of a Milwaukee spade bit extender that's cut down to about 4" long. Don't use a drum much more than half the diameter of the tube ID. Any larger and it will begin orbiting the ID rather than rotating against it. The drill press isn't moving so you are. If it doesn't drop away freely when tilted at an angle, it's likely going to catch, the force will cause the other end do orbit in a larger radius and the tube will break a few finger. Or worse. you can accomplish the same with a drill in a vice or clamped to a table top.

Your best bet is a press fit. The surfaces should be as smooth as possible. If not, you have tiny contact points and alot of air. Even a tiny fraction of a MM is an effective insulator, so the better the contact, the better the heat conductivity. Thermal paste is better than not if you can't get a good interference fit. It's going to be tough to get uniform application with a tight fit so you're back to doing what you can to get the best metal to metal fit possible. The alternative would be to have a larger gap and fill it with a thermal adhesive.

You have to determine how far you want to go and that depends on what you're trying to accomplish. If you're using an XML in a Mag and have an inch-tall heat sink, remove the anodizing and goop it up. If you're putting 10 amps into an SST90 in that mag, find a good machinist.

You can do the basic math for each material interface, beginning at the diode and ending at the exterior of the tube. The numbers are only going to be relative but the exercise will show you where the thermal bottlenecks are. Unless you do that, you're just guessing- and maybe wasting time, effort and money. Nothing is worse than investing in something you enjoy and not being happy with the results. And it's very avoidable. It's a hobby- it should be fun.


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## Justin Case (Dec 6, 2012)

Post deleted.


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## moderator007 (Dec 10, 2012)

The chemical in those drain cleaners you are looking for is caustic soda. I use Roebic drain cleaner 100% caustic soda. Will eat through maglite anodizing in minutes with very little caustic soda in water.


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## BIGWOOD (Dec 10, 2012)

The substance in all those products (Grease Lightning, Drano, Liquid Plumber) is Lye, also known as sodium hydroxide (NaOH), or potassium hydroxide, or the household term, caustic soda. If you are using one of these products, make sure you read the MSDS. The MSDS will tell you what % of lye is contained in the product so you know which product will be more effective compared to the other. Also wear gloves and eye protection. The stuff is seriously alkaline and caustic. It'll give your hands a really nice chemical burn.


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## Justin Case (Dec 10, 2012)

Post deleted.


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## Luciaro (Dec 10, 2012)

ma_sha1 said:


> Arctic Silver 5 is not a glue, I use it for inserting heat sink to flashlight body, so it's removable.
> 
> The two parts Arctic Silver is excellent thermo glue, better than Fujik or Arctic Alumina, I use it for glue down led star
> 
> ...



Thank you


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## CTS (Dec 11, 2012)

If you attempt the chemical method and are just looking to remove the finish from the tube ID, I would avoid masking the finish using any sort of tape. You might want to try coating the exterior of the tube in a coat of grease. I'd use what is commonly called "red grease" That's not the real name, but everywhere you might find it will know what you're looking for- any parts store/Walmart/Etc. After coating, you can wrap in saran to keep the mess down. The reason I suggest red grease is that it doesn't have additives in it that stain your hands or whatever you might get it on. Any grease will work.

Also, if you go with the chemical method, you'll need to smooth up the surface of the bore as the NaOH will etch the surface. Rough surface equals poor thermal conductivity.

Remember there are two components in that anodized finish- the anodizing and the coloring. They anodize them and then dye them whatever color they might use. As I'm guessing you want to go slow and not eat up the tube ID, don't go too slow and only remove only the color. It's very difficult to tell when you have bare aluminum. Probably the best test would be sandpaper. If it's still got anodize on it, the paper won't really bite too well. If it's aluminum you'll get that silver-grey loading in the paper very quickly. I'd suggest 600 grit.


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## Overclocker (Dec 11, 2012)

a few years back i did a TIM comparison between 18 different materials

http://www.overclockers.com/18-way-tim-comparison/


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