Why a good thermal path really matters

[ergotelis]

Just want to provide some feedback on the DX copper star XML, it didn't work,
When I put a light together, it wouldn't lit up, some times emit a blink of light.

I ordered & received another one, same thing, initial test with a battery fine, after soldering
leads onto the star, it no longer work, again some rimes emit a blink of light.

I am down two for two on this Copper start XML, so I am out.

damn i think i will get dissappointed!

@CKOD, excellent work, this shows exactly what i believe too. Also, to validate your results, rerun you test @1amp to see the difference there!

[MikeAusC]

. . . would it help to build a bead of heat conducting goo around the edge the ceramic tile, effectively conducting some heat thu the sides of the tile ? being pretty close to epicenter and all. if that tile is 4mm by 4mm by 1mm thats 16 mm sqared on the base and 16 mm squared on the vertical border surface.
. . .

The best thermal compound has less than one-tenth the conductivity of aluminium - it works under a star only because it's microscopically thin, to fill in air gaps caused by surface irregularities.

Putting a thick bead of it around the edge means the path is very long, rendering it pretty useless.

[CKOD]

I'll be doing a bit more testing, but for that I'm waiting for someone whos been posting a lot in this thread *cough cough* to fix something, and start making some parts *cough cough cough* ( )so I can compare that to the DX board, and maybe the cutter board if I feel like putting a LED back down on it.

[saabluster]

I'll be doing a bit more testing, but for that I'm waiting for someone whos been posting a lot in this thread *cough cough* to fix something, and start making some parts *cough cough cough* ( )so I can compare that to the DX board, and maybe the cutter board if I feel like putting a LED back down on it.

[vestureofblood]

Hey sabluster,

I have bee dong some digging on this but I was wandering what your thoughts on it are.

The data sheet for XML says that max junction temp is 302F (150C). So what I am wandering is if you have determined a relative max temp for the surrounding heat sink. For example I put some XMLs on a copper plate and put a temp sensor in the center of the leds and powered it up. Do you have an idea what point I shut it down should be based on the temp of the heat sink at close proximity to the LEDs?

[saabluster]

Hey sabluster,

I have bee dong some digging on this but I was wandering what your thoughts on it are.

The data sheet for XML says that max junction temp is 302F (150C). So what I am wandering is if you have determined a relative max temp for the surrounding heat sink. For example I put some XMLs on a copper plate and put a temp sensor in the center of the leds and powered it up. Do you have an idea what point I shut it down should be based on the temp of the heat sink at close proximity to the LEDs?

It's not as easy as just specifying a set temp for the heatsink. It can be higher or lower depending on the specific properties of the heatsink and LED used. This data sheet should give you an understanding of the math involved.

[Curt R]

Any new updates? Direct real world testing is very helpful.

Curt

[vestureofblood]

Hey saab,

I am guessing you have also done similar tests with XRE. Could you give me an idea how far it really pays to drive an XRE? I have my LED soldered to a thick copper slug on a heat sink that is mag sized. I need a rough idea of how hard I can drive it and still see gains. I would like the output to be sustainable to at least 30 seconds. Thanks

[bigchelis]

Hey saab,

I am guessing you have also done similar tests with XRE. Could you give me an idea how far it really pays to drive an XRE? I have my LED soldered to a thick copper slug on a heat sink that is mag sized. I need a rough idea of how hard I can drive it and still see gains. I would like the output to be sustainable to at least 30 seconds. Thanks

My Surefire L1 XR-E R2 by Milky is direct drive and pulls 2A off fresh AW 17670 and did 390 OTF lumens. Copper heatsink in L1 bezel and thermal glue paste of some type is what he used. I am sure LED to copper bonding would be better and Sott felt 2A was about perfect for XR-E R2 as long as it had copper. It gets warm quick too. My XR-E R2 was purchased at cutterelctronics and EZ100 type.

[vestureofblood]

Do you guys happen to know if the R2s cutter is selling now are the EZ900s?

[bigchelis]

Do you guys happen to know if the R2s cutter is selling now are the EZ900s?

I called them and just about every reputable LED supplier and they all said no.

bigC

[ma_sha1]

Hey saab,

I am guessing you have also done similar tests with XRE. Could you give me an idea how far it really pays to drive an XRE? I have my LED soldered to a thick copper slug on a heat sink that is mag sized. I need a rough idea of how hard I can drive it and still see gains. I would like the output to be sustainable to at least 30 seconds. Thanks

My Franken Mag Jr. with Cutter XRE R2 EZ1000 bare led, arctic silver glue-down under pressure to copper heat sink in mag C did 221,000Lux @ 1 meter using Dx 66mm Aspheric lens. it's 2.2Amp under direct drive using Panasonic 2900mah 18650.

[vestureofblood]

Wow dude, 221K is right about where I need to be. I upped the current on my light last night from 1.4A to about 2.18A, it did give a bit of a gain I think. I dont have any equipment to test but I think even with the led soldered to the copper slung the Q5 I have on there starts to drop off a bit after 1-2 min. Nothing drastic, but a slight fall. I have also ordered a larger lens to.

FYI I started a group buy in the MP if you guys need anything from cutter right now. I will probly place the order this weekend.

[AaronM]

Is this ceramic stuff any good? Looks pretty neat....

http://www.ceramtec.com/index/produc...t-sink-design/

http://www.aavidthermalloy.com/produ...tors/beryllium

http://www.americanberyllia.com/

[saabluster]

Is this ceramic stuff any good? Looks pretty neat....

http://www.ceramtec.com/index/produc...t-sink-design/

http://www.aavidthermalloy.com/produ...tors/beryllium

http://www.americanberyllia.com/

Yeah that is awesome stuff. Just nothing that I know of made of it that would really be of any use to us.

[AaronM]

It's been about a year since I called them, but I think American Beryllia said they would make stars for around a buck a piece if a guy ordered two hundred.

EDIT: I don't think there is an insulating material between the metalized portion and the main body of the part as the main body is an electrical insulator already.

http://www.americanberyllia.com/manuf_capa.html

http://www.americanberyllia.com/services.html


Another EDIT: Heck, I don't believe my own memory on this one: A dollar each sounds too good.
Anyway, whatever the price was, it seemed fair considering it would be the best star ever.

[bshanahan14rulz]

BeO scares me.

[AaronM]

My glasses are BeCu...and I'm not dead...yet. :/

[MikeAusC]

Berrylium Oxide has the same thermal properties as Aluminium, so all you'd be gaining would be eliminating the electrical insulator between the copper track and the aluminium star - plus you'd have very brittle star !

For significant improvement, you'd use a copper star with the LED soldered directly to it.

[AaronM]

I think the BeO star WOULD be a significant improvement over a typical board.
...Of course you're right, solid copper should be even better, but how? Even the unit in the link below has a gap between the emitter and copper chunk that would need to be filled with solder.

http://www.led-tech.de/de/High-Power...0_120_170.html

The ideal would be to photo-etch the copper so the thermal pad would stand proud a bit and be at the same level as the top of the other layers.

Anyway, this is all speculation and ideas I'd love to see put to the test on my part.
Sometimes an experiment will show unexpected results and I'm cool with that.

[bshanahan14rulz]

http://en.wikipedia.org/wiki/Berylliosis

As long as people use the stars in their stock form without cutting or sanding or grinding, they are completely safe. I myself have a pressurized gas chamber made mostly of BeO in crucial areas, and I am not worried about Berylliosis. Unless I were to drop it and break it, causing BeO dust that may become airborn. But yeah, it's mostly safe.

On a separate idea, what if you cut out the insulating layer below the slug and used, say, indium solder or indium metal to bond it to aluminum. Anybody know if indium will wet aluminum or slightly oxidized aluminum?

[MikeAusC]

. . . . . Even the unit in the link below has a gap between the emitter and copper chunk that would need to be filled with solder. . . . .

You must have something between the LED base and the star - and solder seems too be the best thermal option that's well ahead of any alternative.

[AaronM]

I understand that.
I just object to the rather large gap that needs filling.
The least thickness of something, the better.

[Kinnza]

The key to lowering thermal resistance is to avoid the thermal interface for isolating purposes. The beryllia star accomplish it directly, as it is not electrical conductor, so LED can be soldered directly to the cooper printed on top. You cant do that with a copper star, as you need to isolate the electrical contact from the copper.

Still if you need a thermal interface between beryllia and heatsink, then the full star surface acts transferring all the heat, without the bottleneck that usually happen at the dielectric layer. To get best performance with a copper star, you need one having the area for the thermal slug raised to the level of the circuit on the dielectric covering the star but not the thermal slug (but only valid for LEDs with electrically isolated thermal slug). Once you have the heat spread along the star without any thermal barrier (just the solder interface), thermal impedance is very reduced because you have a surface area many times larger than the initial heat generating source and it is way easier to transfer it away. The key for having the lowest thermal resistance is to be able to spread the heat as most as possible before it must go through a layer with lower thermal conductivity.

[saabluster]

I really don't think this is the best stuff to be using for stars but it would be a fantastic material for LED package construction.

[MikeAusC]

If you're mounting an XM-L or similar LED that has 3 pads on the underside, and the "star" can be connected to LED-ve, you will get maximum thermal coupling if you can solder the large central pad and the -ve pad to the "star".

The +ve pad can then be thermally coupled via an electrical insulator that's as thin as possible.

[Quest4fire]

Can't resist bumping this thought provoking thread. Anything new to report saabluster?

[D0do]

@Saabluster
How did you remove the residue of the mold release agent?
With a Q-tip and some water? Or should one just ignore it?

[saabluster]

Can't resist bumping this thought provoking thread. Anything new to report saabluster?

Not really. Have not had any spare time to play recently. I will say that I noticed Cutter seems to be trying to use better boards as my last order of XP-E had a very nice ceramic isolator instead of the fiberglass.

@Saabluster
How did you remove the residue of the mold release agent?
With a Q-tip and some water? Or should one just ignore it?

Isopropyl alcohol. Don't ignore it though. It could contaminate the dome and turn black over time.

[Shooter21]

i wonder how well a diamond heat sink would work instead of using solid copper?