How to attach a Cree XR directly to a copper plate?

Kinnza

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I want to use the Cree XR directly over a copper plate, but i dont how to do it.

I know the slug is electrically isolated, but what about anode and cathode leads? If i use thermal conductive adhesive to attach it and then wire the electrical contacts, dont go current on copper? (sorry my poor english, hope you can understand what i meaning).

Is there anyway to handsolder it?, or is adhesive required for home made instalation?
 

3rd_shift

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A picture of the led in question may help.
I want to say arctic alumina 2 part adhesive is a good way to go, but I do not even know what the led looks like underneath.

There are members here who are very good at knowing Cree leds.
Maybe one will post about this.
Now I'm kinda curious too.

:popcorn:
 

wmpwi

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I remember seeing a photo of someone testing a cree emitter and had done so by affixing it to a copper plate by using a hot plate or something and just letting the solder flow. Because it was the XLamp, he used a tape of some type to insulate the part. Found it and it was NewBie. The thread was the original cree group buy:

https://www.candlepowerforums.com/posts/916706

That might help.
 
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yellow

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thinking of this also (for when the Q-bin gourp buy really comes into effect):

if Led-connetions are on the top: cut/file the "+" and "-" contact away from the underside.
then:
directly solder the slug to the copper,
or, in case of aluminium heatsink, make it as with the luxeons:
thermal grease on the slug, push it into place (it holds then quite good), glue base and sink together with epoxy glue.
 

ROVER

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I don't remember who came up with this, but as I understand it, you can sand the electical paths off the edges of the bottom, so you're just left with the thermal path on the bottom of the emitter- and then solder your leads to the electrical connections on the top.
 

Kinnza

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Thanks everybody for your help, now i see how to do it.

But maybe would be enough to glue a dielectric layer directly in the bottom area of led's electrical conections? (instead of putting it on the copper, as Newbie).

I like yellow's suggestion of cut/file the bottom of electrical contacts, but im afraid it can damage the led. I prefer to have a confirmation about if this can be done. I have some Cree X7090, the old model, if nobody has done it before, ill sacrifice one or two experimenting :whistle: , i suppose it have the same design.
 

CM

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If possible, it's best to use Cree's on MCPCB stars. I've damaged about four LED's trying to use them as bare emitters without proper reflow equipment.
 

3rd_shift

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The electrodes are 5.6mm apart.
I think it can be done with a 4mm wide copper strip, or block, carefully arctic alumina'ed underneath the led in between the electrodes without touching either one.
Then apply that whole thing to the copper plate with more AA.
The idea is to keep the electrodes from shorting on anything metal, while allowing a good thermal contact surface area.

Then solder the electrodes on top to your connectors with a small pencil type electronics grade soldering iron.

If all goes well, then you can :)
 
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Kinnza

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3rd_shift said:
The electrodes are 5.6mm apart.
I think it can be done with a 4mm wide copper strip, or block, carefully arctic alumina'ed underneath the led in between the electrodes without touching either one.
Then apply that whole thing to the copper plate with more AA.
The idea is to keep the electrodes from shorting on anything metal, while allowing a good thermal contact surface area.

Then solder the electrodes on top to your connectors with a small pencil type electronics grade soldering iron.

If all goes well, then you can :)

Nice idea!:thanks: , it seems the simplest way to go.
 

NewBie

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With common MCPCB's I'm seeing a 10-15C rise between LED and aluminum of MCPCB, and keep in mind, the ceramic substrate in the CREE XR-E isn't the best as far as heat spreading, such that the spot I cannot get to is probably considerably warmer yet, right under the die.

A visual example of the performance drawbacks of common MCPCB's is shown here:

etgmcpcb.png
 

LEDite

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Kinnza;

I've hand soldered about 50 Cree XR directly to copper heatsinks without a single problem.

I precoat the XR with solder and attach a wire to the side of the positive terminal.

Then I heat the copper strip (5/8" x 2.25" x 1/16") and apply solder to the desired area.

Place the XR on the copper strip with the positive terminal hanging off the edge.

Hold down the XR with an exacto knife until set.

Solder a wire to the copper strip for ground and fire it up.

My new XR-E P3 looks very nice by the way.

Larry Cobb
 
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Kinnza

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Thanks again, and specially to Newbie for stoping here, your post reinforce me in the idea of using copper directly.

Hope LEDite's way will be useful for many people mounting the Cree XR-E for flashlights. Not for me now, because my current project isnt a flashlight, but a whole lighting system, conected to 220V plug. Im going to conect about 85w of Cree XR leds in series, so i must avoid any electrical flow in the copper.

My idea is mounting the Crees on a small copper plate and attach it to a copper pipe, wich act as heatsink itself, but aircooled with a DC fan. If my previous math is correct i expect just a 3-4ºC increase of temperature over ambient in the pipe.
 

frenzee

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I don't know if this will work in your situation Kinnza, but I've had good experience isolating Luxeons by spaying a thin layer of sandable high-temp black primer paint on the copper heatsink (You can find the stuff at auto parts stores). I then bake it at 225F for about 10 minutes and inspect it to make sure there was no shrinkage or cracks on the paint layer. Then I can attach the LED with thermal epoxy pretty much anywhere I want.

I have tried AS epoxy alone and various pastes, but I always had problems with shorts. So far this method has worked fine.
 

NewBie

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creesold.jpg


xrecop2.jpg


I've been soldering for 37 years, nearly on a daily basis, and I forget not everyone has this level of experience. I also was certified under the NASA 2000 standard, and spent many months in school and qualification testing. So, I've also been "school trained" for high-relability soldering.

Above are some quick examples on what I did, looks like.

I use Kapton (Polymide 33) tape. Kapton (polymide) tape can typically withstand 7500 Volts, is made for continous use at 356 Degrees F (there are some higher temp rated Kapton tapes, fyi).

Some examples:
http://multimedia.mmm.com/mws/mediawebserver.dyn?6666660Zjcf6lVs6EVs666exXCOrrrrQ-
http://rocky.digikey.com/WebLib/3M/Web Data/5413 Tape.pdf



Where does one obtain it?
http://www.mouser.com/search/refine.aspx?Ntt=polymide
Search on digikey for Polyimide or Kapton

5419 has an advantage over 5313, as it has materials in it that greatly reduce voltages generated when removing the tape, which can exceed 10,000V typical of many tapes.


I simply polish up the surface with steel wool or 3M scratch pad, until it is shiny and clean, and rinse with hot water and soap to remove particles. The copper will take on a light pinkish color when it is properly cleaned. Keep scrubbing for a while beyond where the copper looks clean.

Then I put kapton (polymide) tape down to electrically isolate the ends under the CREE. I then rub it down (burnish), until things look crystal clear, showing that the adhesive is properly attached to the copper.

It takes a good amount of heat to heat up the plate, and I use RMA flux solder (DO NOT USE ACID CORE), and melt it on the area, assuring it is hot enough to flow to the copper and sticks. You want the solder to flow as you apply it, not just melt it on top. I use two soldering irons or a soldering iron and a paint stripper heatgun from Harbor Freight that goes for 9.95. Take your time and don't rush things. Right before I apply the CREE, I like to use the iron as a slag bar, and wipe it across the top, to remove the oxides (slag).

Removing the other heat sources, I keep one iron on the plate to help hold temperature. I then take tweezers and set the CREE on the molten solder. Sometimes I put flux on the back of the CREE, but it really isn't needed, and thus I don't use it much. You can also pre-tin the back, but this takes skill, as most irons are much hotter than what the CREE should be exposed to, and the lack of thermal mass makes this a dicey operation. This tape prevents the solder from flowing across the copper, and works better if you rub or burnish down the tape.

Once the solder flows to the CREE, I then brush on isopropyl alcohol to quickly cool the plate down. Sometimes I use forceps/pliers/tongs, to pick up the plate and set it on shallow water or isopropyl alcohol. Not deep enough to wet the LED though.

I suggest you solder your wires to the CREE ahead of time if possible, or at least pre-tin the pads (I usually connect to the top side).

As I mentioned in the other thread, if I was learning, I'd highly recommend that you get a hold of several of the low cost red CREE LEDs, XL7090 or XR7090 for practicing the technique.


If you are going to be soldering on your CREE LEDs, make sure that you have "dehumidified" (baked) them first, or they were stored with desiccant and the indicator still indicates things are dry. Failure to do so, will result in weird things to the gel and phosphor inside, and a dramatic loss in light output. It can also result in color shift in the output. This is not a problem if you are not soldering them.

The process for dehumidifying them is found here, bottom of page 3:
http://www.cree.com/products/pdf/XLampSolderingandHandling.pdf
 
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KWillets

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The XR-E datasheet lists a max temp of 260 C = 500 F, for 30-90 seconds. Remarkably similar to pizza.

Actually, I did some searches of this forum and found a few mentions of this product line. Apparently it is reflow solder paste, repackaged in a small size, so it's a good option.
 
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