Grapchite PCB?!

As far as I have read, graphite is best material for heat removal. So I started to look for graphite PCB, found just one :shakehead company, got reply from them:


What do you think? Anybody tried?

Also, some interesting info here:
http://www.graftechaet.com/eGRAF/eGRAF-Products/SPREADERSHIELD-2-D-Heat-Spreaders.aspx
"Engineered thermal conductivity 300-500W/m-K outperforms Copper and Aluminum"

Graphite is electrically conductive, so it won't fly because of parasitic drain.

kwkarth said:

Graphite is electrically conductive, so it won't fly because of parasitic drain.

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I`m sure it can be solved with some non electrically conductive layer. They sent me this pic, so it means, they have solution for it.

RobEU said:

I`m sure it can be solved with some non electrically conductive layer. They sent me this pic, so it means, they have solution for it.

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I guess we'll have to just wait and see, because as they create an electrically insulating layer, so too, will they thermally insulate, and then, we're back to square one. Further, because of the currents involved, there will eventually be dendrite growth problems.

What's the price on those?

saabluster said:

What's the price on those?

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Dont know yet. Have to decide is they are any good before asking for a price

Strange thing, sounds so good, but just few manufacturers on the globe doing this.

Looks to me like the best application of this technology is to STOP heat conduction in one plane and confine it to another. Cool idea (pun intended) but in a flashlight application, it doesn't seem to be a great fit, does it?

kwkarth said:

Looks to me like the best application of this technology is to STOP heat conduction in one plane and confine it to another. Cool idea (pun intended) but in a flashlight application, it doesn't seem to be a great fit, does it?

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Yeah I think you are right. How the heck you are supposed to then get the heat out using the thin sides baffles me.:shakehead

kwkarth said:

Looks to me like the best application of this technology is to STOP heat conduction in one plane and confine it to another. Cool idea (pun intended) but in a flashlight application, it doesn't seem to be a great fit, does it?

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I am planning to use it in outdoor LED street light.

RobEU said:

I am planning to use it in outdoor LED street light.

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I can't see how this technology will benefit you, but then maybe I just don't understand what you have in mind. Why would you need to confine heat conduction to one plane, and how would that benefit your cause?

kwkarth said:

I can't see how this technology will benefit you, but then maybe I just don't understand what you have in mind. Why would you need to confine heat conduction to one plane, and how would that benefit your cause?

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I`ll put it stright I am looking to build myself an outdoor LED light. But I dont want just take usual PCB and chunk of aluminium, anybody can do that(buy leds soldered to star, buy CPU heatsink with fan). My goal is to find ultimate material for best heat removal, have good thermal management and have low Tj light whith high lumen output. It will be my first LED light in my life, so I am spending lot of time reading and searching for materials(like before first sex ). Because my english is not perfect, I might be misunderstanding some things, so, forget me for that I have found leds i might be using: Cree XP-G or OSRAM Golden Dragon oval Plus.
As far as I understand, graphite removes heat away from heat source much better than anything else, what is perfect for PCB for LED. Or I am not understanding it correctly?:thinking:

RobEU said:

I`ll put it stright I am looking to build myself an outdoor LED light. But I dont want just take usual PCB and chunk of aluminium, anybody can do that(buy leds soldered to star, buy CPU heatsink with fan). My goal is to find ultimate material for best heat removal, have good thermal management and have low Tj light whith high lumen output. It will be my first LED light in my life, so I am spending lot of time reading and searching for materials(like before first sex ). Because my english is not perfect, I might be misunderstanding some things, so, forget me for that I have found leds i might be using: Cree XP-G or OSRAM Golden Dragon oval Plus.
As far as I understand, graphite removes heat away from heat source much better than anything else, what is perfect for PCB for LED. Or I am not understanding it correctly?:thinking:

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Have you compared their specs with plain aluminum?

kwkarth said:

Have you compared their specs with plain aluminum?

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Yes. Aluminium is 170-230. Graphite 300-500W/m-K.

RobEU said:

Yes. Aluminium is 170-230. Graphite 300-500W/m-K.

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Admittedly, I did not spend more than a couple minutes skimming through the web site you linked and another that they linked, but your need is 3D heat removal and not 2D heat removal. In the last illustration you posted, you can see it is designed to transfer heat from the contact point in the center out to the edges of the material. I can't imagine that scenario in a flashlight. There is nothing you need to protect from heat behind the LED and how do you efficiently couple the edges of that material for further heat sinking away from the LED. The whole thing looks like a constraint rather than an assist in moving heat from the LED. There is no thermal mass to the graphite stuff o you have to move the heat somewhere else to dissipate it.

I`m not building flashlight, bet outdoor streetlight.
Check this link for 3D version:
http://www.graftechaet.com/eGRAF/eGRAF-Products/SPREADERSHIELD-3-D-Heat-Spreaders.aspx

I will have heatsink.

RobEU said:

As far as I have read, graphite is best material for heat removal. So I started to look for graphite PCB, found just one :shakehead company, got reply from them:

What do you think? Anybody tried?

Also, some interesting info here:
http://www.graftechaet.com/eGRAF/eGRAF-Products/SPREADERSHIELD-2-D-Heat-Spreaders.aspx
"Engineered thermal conductivity 300-500W/m-K outperforms Copper and Aluminum"

Click to expand...

Thermal conductivity in the Z direction means that's how conductive it is when moving heat from the top of the square to the bottom.

I suspect the reason their numbers are so low in the Z direction is that there is a layer of insulation between the thermal pad and the graphite substrate. If you are using Cree LEDs, you don't need to electrically isolate the thermal pad from anything, as it is already isolated from the LED anyways. So, you might be able to scrape up some of that insulation on the board and mount the thermal pad directly to the graphite, a-la artic silver 5 or ceramique.

This, of course, is assuming the company makes a gcpcb for cree LEDs. Could always epoxy the cree with thermal epoxy and use strips of metal to connect the LED pads to the gcpcb pads...

Why not just mount the LEDs directly to a copper heatsink?

RobEU said:

I`m not building flashlight, bet outdoor streetlight.
Check this link for 3D version:
http://www.graftechaet.com/eGRAF/eGRAF-Products/SPREADERSHIELD-3-D-Heat-Spreaders.aspx

I will have heatsink.

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Ok, so size and weight are not limitations, right?

Look carefully at the 3D "spreader" you linked to. See what they use as a critical component of that product? ALUMINUM.

It will cost you 20x to go that route rather than to stick with plain aluminum. Why do you want to go that direction?

bshanahan14rulz said:

If you are using Cree LEDs, you don't need to electrically isolate the thermal pad from anything, as it is already isolated from the LED anyways.

Why not just mount the LEDs directly to a copper heatsink?

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I dont know which I am going to use, I have choice between Cree XP-G or OSRAM Golden dragon oval Plus/Dragon plus as they are only ones which fit my requirements. But I am leaning OSRAM way as their customer support is superb, fast and prompt replies, also huge library of information about their products +partners list who specialize in optics, thermal and electronics with OSRAM products. It will be more easy to make a product with Osram.

Copper is very heavy, also more expensive. One of my goals is to make small, thin and lightweigt lamp.

I'm not going to reinvent the wheel if I'm making a new car. Could be the engineer in me speaking but I think you are making this project too complex.

How thin and how light? Also how much output do you want from the lamp?

If I wanted a thin and light streetlamp with 1000 lumen from a 110-220v source (thin being less then 2 inches). I'll get 6 Cree XP-G R4 or R5s, drive them in series at 500-600 mA, and thermal epoxy them on a 6x3x1"slab of Al (or whatever the closest "standard" size is) for the heatsink and use 4 strips and 1 sheet of frosted acrylic or other good light transmitting plastic to make the enclosure. The driver will be in the base of the lamp.

Maybe the CreeBar can give you some ideas. Here's a thread about one.

In the end, it is your project. Who knows, maybe you'll come up with something really different.

Gunner,

Probably, but just a littble bit. Chunk of aluminium is quite heavy, I want to avoid huge weight. I am targeting around 2700 real lumen output, 4500-5600K, max 40w total consumption, max total weight 2kg, working from 220v source.

Thank you for the link, that will help.