Copper mini heatsinks for Cree XR-E LEDs

[Erasmus]

Ever since these amazingly bright LEDs are on the market, it's a PITA to mount the bare emitters. Of course there are some solutions for this :

• chop away the corners : makes soldering the wires a PITA and thus some reflectors won't be focussed properly
• grind away the electrical paths on the bottom : takes some work and you still have to connect the wires on the top, which can give focussing problems for reflectors
• buy them on a PCB : poor thermal transfer which is not good for the LED (decreased lifetime and decreased output)
• buy them on PCB's with thermal via's : good solution, but quite expensive

I've been thinking for a while and today I made some sketches for a good solution: small copper heatsinks which you can solder to the thermal path on the bottom of the LED. Advantages?

• no need to chop away the corners of grind away the paths on the bottom
• excellent heat transfer
• wires are connected on the bottom, so no more problems with focussing reflectors
• easily mountable on a bigger heatsink

Here are some of the sketches of different designs :



Model 1 : is about the size of the emitter which makes it possible to put emitters right next to each other

Model 2 : mini-size, makes me think about the copper spacer in my Lummi Wee flashlight

Model 3 : same as model 2, but with 9mm diameter round path for easier mounting on a bigger heatsink

Model 4 : 14mm round disc with 2mm holes, perfect for attachment with M2 screws

Just some crazy ideas, let me know what you think of it

Cheers!

 

[darkzero]

Great ideas. I like them all! I'd definitely would like to buy a number of model 2!

 

[Firecop]

I'll second that!

 

[1 what]

Hi Erasmus,
Thought you might be interested in these.

Consider it my free prototyping service.
A friend made them for me just after the Q5's were released. I wanted to get a CREE into a large reflector but thats another story.
They work very well. I've got a cut down one in another small flashlight. Copper is wonderful stuff!

 

[Illum]

I've been thinking of something like this...
I bought a couple aluminum charging spacers, sanded the sides and AA'd it to a USWOL emitter, it seems to perform fairly well drawing heat out of them.
I think if they are made in copper they would work very well.:twothumbs

 

[Erasmus]

I contacted some factories which might get this done for us

 

[2xTrinity]

Of the ones you prototyped, model 4 is definitely the best -- since you're going to be introducing an extra thermal interface compared to mounting the LED directly to the main heatsink, this extra mini-heatsink/main heatsink junction should be made as large as possible, to minimize the amount of thermal resistance added to the final system.

 

[saabluster]

Ever since these amazingly bright LEDs are on the market, it's a PITA to solder the bare emitters.

Well I don't think Crees are very hard to solder at all. It was at first but now I have developed a technique that makes it very easy. Also I am already using copper in almost the exact way you have the model 1. It works very well for when you can't solder to the top. I think of all of these models by far the best is #4. It would give you the option to use a solder paste instead of needing an epoxy or solder to hold it down. :twothumbs That is just genius. Good job.

 

[VanIsleDSM]

Something I've considered before myself.

The absolute best way would be to have the raised chunk of copper protruding through the middle of the PCB, machined perfectly flat.. so you can still SMT the LED so you have maximum area for heat transfer.. even if it's not the thermal pad, it still helps. And there would be nothing between the LED and the copper but solder.. But then there's still the need for SMT soldering.

I've been meaning to look into finding a PCB maker that can make some super thin FR-4 with tons of tiny thermal. I'd like to get some made for rebels and Crees.. I think SMT is the best option.. and it's not that hard to do.

Very nice models by the way.

 

[Erasmus]

Well I don't think Crees are very hard to solder at all. It was at first but now I have developed a technique that makes it very easy. Also I am already using copper in almost the exact way you have the model 1. It works very well for when you can't solder to the top. I think of all of these models by far the best is #4. It would give you the option to use a solder paste instead of needing an epoxy or solder to hold it down. :twothumbs That is just genius. Good job.

I just saw I made a mistake there, I wanted to say "a PITA to mount" instead of "to solder". Soldering is quite easy, but mounting them in a way to avoid all the listed disadvantages is just impossible.

I never worked with solder paste but for sure I'm going to try it out after my exams. Is there any basic tutorial for this?

 

[Erasmus]

Something I've considered before myself.

The absolute best way would be to have the raised chunk of copper protruding through the middle of the PCB, machined perfectly flat.. so you can still SMT the LED so you have maximum area for heat transfer.. even if it's not the thermal pad, it still helps. And there would be nothing between the LED and the copper but solder.. But then there's still the need for SMT soldering.

I've been meaning to look into finding a PCB maker that can make some super thin FR-4 with tons of tiny thermal. I'd like to get some made for rebels and Crees.. I think SMT is the best option.. and it's not that hard to do.

Very nice models by the way.

I also thought about that but like you say reflow soldering is still necessary to put everything together, while the designed heatsinks are made for hand soldering which is more convenient for most of us. Will think about the SMT options though

 

[wildstar87]

Seems to me that Model 4 is pretty much like a 14mm star, like this...

http://www.dealextreme.com/details.dx/sku.11023

I dunno if the copper would be that much more thermally efficient than a star already mounted, with the mass involved. And wires wouldn't be mounted directly on the top of the LED with the star anyway. Not trying to be a wet blanket on this, but I guess I would be more interested in something like Model 1 or 3.

I suggested this a while back, but I thought what would be cooler, would be a heatsink that would make interchanging Cree emitters a snap, something like a CPU socket, some metal contacts either on the top or bottom that you could solder to, that would then contact the led's contacts. A clip would hold down the LED, with some small screws or something like that.

That way when a new bin comes out, you just unscrew the clip, pop the old led, and pop in the new one, screw the clip back down, you are back in business, probably less than a minute to change out.

 

[mpf]

I have had some experience SMD soldering Crees to copper blocks

It is pratical using a heat gun and a thermocouple multimeter and SMD solder paste. You just have to remember to make the connections to the Leds first because once the Leds are mounted you cannot get enought heat into the led to solder wires on.

In the picture above I premounted the leds on the PCB and then soldered the 12 of them to the copper heat sink.

matthew

 

[12Johnny]

I have had some experience SMD soldering Crees to copper blocks

In the picture above I premounted the leds on the PCB and then soldered the 12 of them to the copper heat sink.

WOW!!!

 

[saabluster]

I just saw I made a mistake there, I wanted to say "a PITA to mount" instead of "to solder".

Well that makes two of us. I meant to say thermal paste not solder paste.

 

[saabluster]

I have had some experience SMD soldering Crees to copper blocks

Excellent job!

 

[mikeh]

buy them on a PCB : poor thermal transfer which is not good for the LED (decreased lifetime and decreased output)

So how is this any better than buying a stock MCPCB-mounted emitter?
What are the numbers?
I expect the main difference is in using solder rather than thermal adhesive?
Does the use of copper over aluminium make a significant difference?

Cree quote 8degC/W thermal resistance from junction to base, but its very hard to find data on the resistance of the stars. Does anyone have estimates for the stars sold by DX, Kai etc.?
How would you go about testing it?

 

[Erasmus]

So how is this any better than buying a stock MCPCB-mounted emitter?
What are the numbers?
I expect the main difference is in using solder rather than thermal adhesive?
Does the use of copper over aluminium make a significant difference?

Cree quote 8degC/W thermal resistance from junction to base, but its very hard to find data on the resistance of the stars. Does anyone have estimates for the stars sold by DX, Kai etc.?
How would you go about testing it?

I don't have the devices to measure this myself, but in some posts of Newbie there was a lot of info about this topic. Can't find it at this moment, might search for it later.

I'm working on these heatsinks to get some production of model 2 and model 4