# Thermal Paste In Between Star and Heatsink



## ExtremeSeries (Jan 29, 2014)

Hi all!

Sorry if this has been discussed in depth before (please point me to any thread). I have seen some people suggesting thermal paste (not adhesive) in between the star and heatsink followed by epoxy on the outside. May I ask if anyone actually have done this and have done any test on it? Is it possible without any screwing down involved? I am thinking to apply the paste, clam the star and heatsink and epoxy on the outer edge.

Also, would like to know which type of epoxy you used.

Thank you in advance.


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## Norm (Jan 29, 2014)

I use Arctic Alumina it isn't expensive, IMHO using the right solution is always easier rather than trying to cut corners.

This is a topic that has been covered in the past, opinions vary.

Norm


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## ExtremeSeries (Jan 29, 2014)

Norm said:


> I use Arctic Alumina it isn't expensive, IMHO using the right solution is always easier rather than trying to cut corners.
> 
> Norm



I agree with you. But unfortunately, (good) thermal adhesive is not easily found in the place I live. I have bought a set once and it went bad in less than a year.


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## Norm (Jan 29, 2014)

Where do you live?

Arctic aluminal thermal paste + epoxy = thermal glue? 

Norm


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## ExtremeSeries (Jan 29, 2014)

Norm said:


> Where do you live?
> 
> Arctic aluminal thermal paste + epoxy = thermal glue?
> 
> Norm



Thank you! Exactly what "yellow" said in the third post. Did any of the members have a discussion about it? Or proved that it is doable?


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## schizeckinosy (Jan 29, 2014)

I use system3 t88 epoxy mixed 1:1 with zinc oxide powder for my thermal glue. Performance is excellent.


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## ExtremeSeries (Jan 30, 2014)

Actually, will any expoxy work? I have seen one that states it will soften at 60 degrees C though.


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## schizeckinosy (Jan 30, 2014)

All epoxies soften somewhat with heat. Some soften with time as well. 5-min is the weakest. I use t-88 because it is structural and has good properties. Its main use is laminating aircraft parts.


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## ExtremeSeries (Feb 10, 2014)

Thanks for all the help above! Have two small questions that probably do not need to be on a thread on their two.

I powered the LED (XM-L2) briefly and noticed there is a yellow tint light on the outer edge. The center looks fine though. Is this normal? This is without any reflector/lens. Just the heatsink, LED and wires. Secondly, can alcohol be used to clean the dome of the LED? Looks like there are some specks of dust or glue on it. And the dome feels soft.


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## schizeckinosy (Feb 10, 2014)

I would not worry about what the LED looks like. Shine it on a wall and judge the color that way. Also, alcohol is proper for cleaning the LED, as per CREE:

"Don’t use unspecified chemical liquids to clean the LED; the chemical could harm the LED. When washing is
necessary, please wipe the LED with alcohol at normal room temperature and dry at normal room temperature
for 15 minutes before use."


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## ExtremeSeries (Feb 15, 2014)

Thank you for the clarification.

I have two different setups:
1. XM-L, Aluminium star, Arctic Alumina Thermal Adhesive, Aluminium heatsink
2. XM-L2, Copper star, some thermal compound and epoxy outside star, Aluminium heatsink

I injected 3Amps directly to both LEDs and used a cheapo infrared thermometer and sweep around to find the highest temperature. Both are hitting 90+ and 100+. Am I doing something very wrong?

Edit: Forgot to mention temps are in degree Celsius.


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## schizeckinosy (Feb 21, 2014)

Can we assume that your copper star has the LED directly soldered to it in all 3 positions? That is the only way to get the copper advantage. Also, I'm not sure you can accurately measure junction temperature with an infra-red thermometer. The reading beam is too large and imprecise. What you want to look for is how the LED handles higher amps - and for an XLM on copper you need to go higher than 3. Google up the XML on copper lumen chart from "Match" and you will see much higher power levels before the advantage of copper is obvious.


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## ExtremeSeries (Feb 21, 2014)

schizeckinosy said:


> Can we assume that your copper star has the LED directly soldered to it in all 3 positions? That is the only way to get the copper advantage. Also, I'm not sure you can accurately measure junction temperature with an infra-red thermometer. The reading beam is too large and imprecise. What you want to look for is how the LED handles higher amps - and for an XLM on copper you need to go higher than 3. Google up the XML on copper lumen chart from "Match" and you will see much higher power levels before the advantage of copper is obvious.



The LED + copper star I bought is those usual Noctigon ones and are soldered and so, I am guessing it is a "yes" to your first question. What I am really worried is the heat transfer from the copper star to the heatsink. The heat is too hot to touch and I am guessing it is a good sign that the transfer is working. But this test is done in an open air environment and I am also guessing that after inserting to the Maglite body, the whole setup may be "suffocated" and temps will rise even more (although I also wonder the heat travelling to the body of the Maglite will help enough).


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## degarb (Feb 22, 2014)

schizeckinosy said:


> I use system3 t88 epoxy mixed 1:1 with zinc oxide powder for my thermal glue. Performance is excellent.




Where do you get zinc oxide powder?


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## schizeckinosy (Mar 6, 2014)

Sorry, I missed this post. I use pharmaceutical grade powder (for skin creams, etc.) I get it from suppliers through Amazon. There are several.


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## schizeckinosy (Mar 6, 2014)

For sure you should firmly attach the heatsink to the mag body, wither mechanically or with a press fit and thermal paste to transfer the heat to the Mag and thence to your hand.



ExtremeSeries said:


> The LED + copper star I bought is those usual Noctigon ones and are soldered and so, I am guessing it is a "yes" to your first question. What I am really worried is the heat transfer from the copper star to the heatsink. The heat is too hot to touch and I am guessing it is a good sign that the transfer is working. But this test is done in an open air environment and I am also guessing that after inserting to the Maglite body, the whole setup may be "suffocated" and temps will rise even more (although I also wonder the heat travelling to the body of the Maglite will help enough).


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## degarb (Mar 27, 2014)

schizeckinosy said:


> Sorry, I missed this post. I use pharmaceutical grade powder (for skin creams, etc.) I get it from suppliers through Amazon. There are several.



So, I have been thinking of this route. How far does a pound of zinc go? What is your mixing ratio?

I am guessing original 6900 psi jbweld (works on plastic too) with %20 to %50 by volume of zinc mixed in. 

Maybe mixed outside, if zinc as bad as lead for kids.

Also, to note, I ran across jbweld steel reinforced epoxy yesterday. But pulling up the msds, only %1 ferrosilicon. So, at first glance, not enough metal to do anything other than a marketing label on package. But see below on Actic Silver/alumina numbers..?


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## alpg88 (Mar 27, 2014)

schizeckinosy said:


> Also, I'm not sure you can accurately measure junction temperature with an infra-red thermometer. .



you can't really mesure die temp. the closest you can do is to mesure the star temp, and not with ir termometer. you need contact probe. than you can somewhat guesstimate die temp.i usually go by, die temp is about 20c higher than star (dircet connect) temp. i might be wrong with 20c, but i have not fried a single led using this number yet. when heatsink, gets 75c i trim down current or shut of led.

and i would recomend if there is no right paste available, just polish heatsink\star, and press them hard using screwes, or by pushing reflector down, you will have better heat transfer, with no paste and polished\pressed hard together parts than if you used some diy paste and rough surfices that are loose.


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## degarb (Mar 27, 2014)

Arctic Alumina:

Aluminum Oxide 10 mg/m3 


Artic Silver 5:

Silver 0.1 mg/m3 
Boron Nitride 10 mg/m3 
Zinc Oxide 10 mg/m3 (dust) 
Aluminum Oxide 10 mg/m3 (dust)

If memory serves, 1 cubic meter is 1000 liters, and 1 liter is 1000 milliliters. Maybe 1 gram of zinc is 50 milliliters of epoxy? Seems like a tiny amount.


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## schizeckinosy (Mar 27, 2014)

degarb said:


> So, I have been thinking of this route. How far does a pound of zinc go? What is your mixing ratio?



I use about 1:1 zinc oxide to epoxy. So far a pound is lasting forever!


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## schizeckinosy (Mar 27, 2014)

alpg88 said:


> and i would recomend if there is no right paste available, just polish heatsink\star, and press them hard using screwes, or by pushing reflector down, you will have better heat transfer, with no paste and polished\pressed hard together parts than if you used some diy paste and rough surfices that are loose.



I agree here - ideally, the surfaces would be perfectly flat and pressed together, then no need for any heat paste. But, if your parts ever come loose, the LED will FRY. I see adhesive and heat paste as security for an imperfect world...


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## degarb (Mar 27, 2014)

schizeckinosy said:


> I agree here - ideally, the surfaces would be perfectly flat and pressed together, then no need for any heat paste. But, if your parts ever come loose, the LED will FRY. I see adhesive and heat paste as security for an imperfect world...



I ordered 1 zoom xml a month or two ago from cndirect. I was playing around with altering the aspheric with a tir or reflector. I didn't realize the only thing heatsinking it was the optic pushing the star back to rim of housing. A short bit of playing and I started smelling buring plastic. It was dead before I realized what was likely happening. Fortunately, I didn't like the otf lumens and the heavy weight, anyway. I didn't cheat and claim it was defective from factory, though time of ownership was probably a day.

Also, paste may be lighter than screws on weight sensitive designs. I would guess. 

Also, the cheapest temp probe (not hit hard yet on research) is the $60 RS MM. So, I guess the ir reading say little; but, how far off do you think?

Also, may not be hard or costly to apply thermal grease. Don't see downside to that. I need to break apart my generic china headlamps and put in grease or AA. My ir reading on these stars seems higher than than my homemade lights. I think they have no thermal grease or thermal epoxy--just press things together. The rattle in one head, make me nervous. I will wait for my zinc to come and some weekend before ripping the heads apart.

1:1 looks way better than AA/AS, if I am reading msds correctly.


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## degarb (Apr 19, 2014)

schizeckinosy said:


> I use about 1:1 zinc oxide to epoxy. So far a pound is lasting forever!



I just mixed my first JBWeld with zinc, hoping to create a thermally conductive bond, with no electrical conductivity. I am reliant in this build on the steel like bonding strength. So far, about 3 hours and she is still quite tacky. So, I think, it slows the setting time.

I hope it hardens over night. But in future, in a build where I need bond and thermal, I may be forced to use AA and surround it with the slow zinc-jbweld.


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## sadtimes (Apr 19, 2014)

AA makes a paste that is a thermal epoxy, it sets up hard, you cant break the bond without running the items you bonded. I use it to set SST-90s on heatsinks, I messed one up and I couldnt even dremel the stuff off the heatsink. It does not conduct electricity either. Oh, and its not expensive and sets in about half an hour.


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## degarb (Apr 20, 2014)

degarb said:


> I just mixed my first JBWeld with zinc, hoping to create a thermally conductive bond, with no electrical conductivity. I am reliant in this build on the steel like bonding strength. So far, about 3 hours and she is still quite tacky. So, I think, it slows the setting time.
> 
> I hope it hardens over night. But in future, in a build where I need bond and thermal, I may be forced to use AA and surround it with the slow zinc-jbweld.



24 hours and it was hard. The jbs weld zinc mixture appears to be coonducting heat. Just, judging by one batch, no quick grab.


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## magnum78 (May 1, 2014)

the simplest and the cheapest thermal paste by mixing silicone oil or silicone emulsion with zinc oxide.
you can add silicon carbide, graphite, nano diamond, boron nitride, magnesium oxide, aluminum oxide, or silver oxide to increase thermal conductivity. just remember don't add more than 30%.


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## PFlexPro (May 17, 2014)

One important aspect of 'mixing your own' thermal adhesive or thermal paste is to keep it thin. Look for very low viscosity epoxies that have a maximum temperature of at least 125C. When you start mixing in a thermally conductive additive, it will become thicker. The best thickness is one where you can press the star and squeeze out any excess and achieve metal to metal contact. This way, the thermal paste or glue is only filling the voids and not stopping good metal to metal contact where the surfaces can mate. 
You can test your viscosity by mixing a little, applying it to a star and press it to a piece of glass -about 95% of the thermal compound should squeeze out. Look at the backside (through the glass), If you don't see fairly clean metal making direct contact with the glass, it's not pressed firmly enough or the thermal compound is too thick.

I normally use a commercially available low viscosity thermal epoxy, but when I want the bond to be removable, I use a pourable potting silicone with aluminum oxide mixed in.


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