# Grapchite PCB?!



## RobEU (Dec 3, 2009)

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"


----------



## kwkarth (Dec 3, 2009)

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


----------



## RobEU (Dec 3, 2009)

kwkarth said:


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



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.


----------



## kwkarth (Dec 3, 2009)

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.



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.


----------



## saabluster (Dec 3, 2009)

What's the price on those?


----------



## RobEU (Dec 3, 2009)

saabluster said:


> What's the price on those?



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.


----------



## kwkarth (Dec 3, 2009)

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?


----------



## saabluster (Dec 3, 2009)

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?


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


----------



## RobEU (Dec 3, 2009)

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?



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


----------



## kwkarth (Dec 3, 2009)

RobEU said:


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



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?


----------



## RobEU (Dec 3, 2009)

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?



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:



​


----------



## kwkarth (Dec 3, 2009)

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:
> 
> 
> ...


Have you compared their specs with plain aluminum?


----------



## RobEU (Dec 3, 2009)

kwkarth said:


> Have you compared their specs with plain aluminum?



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


----------



## kwkarth (Dec 3, 2009)

RobEU said:


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



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.


----------



## RobEU (Dec 3, 2009)

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.


----------



## bshanahan14rulz (Dec 3, 2009)

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:
> 
> 
> 
> ...



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?


----------



## kwkarth (Dec 3, 2009)

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.



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?


----------



## RobEU (Dec 4, 2009)

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?



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.


----------



## Gunner12 (Dec 4, 2009)

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.


----------



## RobEU (Dec 4, 2009)

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.


----------



## kwkarth (Dec 4, 2009)

RobEU said:


> 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.


You must have something other than a "Streetlight" in mind. Are we working with a language barrier here?


----------



## Gunner12 (Dec 4, 2009)

A chunk of Al 15x7.5x2.5cm is around 760 grams. If it's a finned heatsink, kinda like a CPU one, then it can be even lighter and the large surface area will help transmit the heat to the air. Or it can be larger at the same weight and be able to cool the LEDs better.

The SST-90 is available in 5700k, but anywhere close to that could be cool tinted. If 5700k is fine though, then 3 SST-90s at around 4 amps each could work. But for the price, a few other LEDs could also be an option. This thread (white LED testing) could be helpful. Check the last few pages for more recent high power LED testing.


----------



## IMSabbel (Dec 4, 2009)

bshanahan14rulz said:


> 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.



No, the reason their numbers are so low in z-direction is the fact that graphite has a very good heat conductivity inside its graphene layers, but no good coupling between the layers.

This _can_ make sense in application terms as a replacement for heatpipes if you have really constrained space situations, for example if you have a chip sandwitched between two pcbs and want to extract the heat out of the gap to the side where the real heatsink is, while not heating up the other side unneededly. 

But for anything LED this is totally pointless.


----------



## RobEU (Dec 4, 2009)

IMSabbel said:


> But for anything LED this is totally pointless.



:twothumbs End of story, thanks.

Could you please comment these two if I would benefit using any of them:
http://www.bergquistcompany.com/thermal_substrates/LEDs/hpl.html
http://www.stablcor.com


----------



## RobEU (Dec 4, 2009)

Gunner12 said:


> 3 SST-90s at around 4 amps each could work.



Thanks. Looks like I just need to cut one piece and weight it. Doesnt sound so heavy from your numbers. Leds are most efficient when driver at low current. So far I have read that 350mA is most efficient :thinking:


----------



## RobEU (Dec 4, 2009)

kwkarth said:


> You must have something other than a "Streetlight" in mind. Are we working with a language barrier here?



I mean this kind of outdoor street light for such an application:




​ 
I do understand english well(can read, write as well, even sing), but some specific technical terms I dont know. Also my lack of electronics experience is making this hard for me. But I am so desparate to learn. One day I will start manufacturing led lights, trust me


----------



## space (Dec 4, 2009)

Going for a PCB with 100x better heattransfer that what is normaly used, will not gain you anything. The clue is getting good heattransfer from the heatsink to ambient (the air). This is where you can improove efficiency. If efficiency is really vital, then running many LED's at lower currents is the only way. 

space


----------



## RobEU (Dec 4, 2009)

space said:


> Going for a PCB with 100x better heattransfer that what is normaly used, will not gain you anything. The clue is getting good heat transfer from the heatsink to ambient (the air). This is where you can improove efficiency.



Oh, why did you tell me that just now? I have spent nearly a week on this, but you just crushed all that in a minute  Wasted so much time. Then only two choices - aluminium or copper. Copper is heavy un much more expensive, so that leaves just aluminium. But I did read that there are few types of them, some being much better than others. Depending on chemical content I think. Have to contact SAPA group then, they seem to be pro`s in this field.


----------



## space (Dec 4, 2009)

RobEU said:


> Oh, why did you tell me that just now? I have spent nearly a week on this, but you just crushed all that in a minute  Wasted so much time. Then only two choices - aluminium or copper. Copper is heavy un much more expensive, so that leaves just aluminium. But I did read that there are few types of them, some being much better than others. Depending on chemical content I think. Have to contact SAPA group then, they seem to be pro`s in this field.



Sorry about that. Not my intention to kill your enthusiasm. Spending time on learning up on new exiting stuff, even if it doesn't end up as "use full", is what I do must of my spare time, and I love it.

It is very easy and often occurring when starting exploring new fields, to get sidetracked by going into small (but in it self important) details, and loosing sight of the bigger picture. Especially so when one get exited. Getting to see the bigger picture is usually quite difficult (read time consuming). More than 99,99...% of the time, ideas that come to mind, have been thought of, developed and improved upon many times by others. And often shared on our fantastic Internet. Spending time to find this info is often the fastest route (but may not the most exiting). That being said I believe that thinking up, to one self, new ideas, can be just as or even more rewarding that reading what other people has though of. 

Good luck with your project!


space


----------



## Illum (Dec 4, 2009)

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.



is, we call that pcb, and it is an exceptionally good material to inhibit thermal dissipation


----------



## znomit (Dec 4, 2009)

I agree this is a solution for a problem that doesn't exist. 
For streetlights you want very long lifetime so you will drive at lower currents where heat isn't such an issue. Space is likely not an issue either given that 15 XPGs at 500mA will meet you lumen goals, any money spent on fancy PCBs would be better directed to a larger lighthead and more LEDs. 

Personally I would like to see motion/rain detectors built in too. 

Your biggest issue will be choosing LEDs that will still be in production in ten years when you need to swap out the light head. But by then you would have sold you company $$$ and be living on a moderately sized private island somewhere nice.


----------



## Gunner12 (Dec 4, 2009)

Sorry, could have saved you some time if I knew you were trying to get the best way to get heat from the LED to heatsink.


----------



## saabluster (Dec 5, 2009)

space said:


> Going for a PCB with 100x better heattransfer that what is normaly used, will not gain you anything. The clue is getting good heattransfer from the heatsink to ambient (the air). This is where you can improove efficiency.
> space


You've got things backwards. It gets more and more important to have high performance materials the closer to the LED die you get.


----------



## RobEU (Dec 5, 2009)

kwkarth said:


> 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.



That contact point is LED junction. But isnt it a main target, to remove heat from LED junction? Is this case this 2D sounds right.


----------



## RobEU (Dec 5, 2009)

space said:


> Going for a PCB with 100x better heattransfer that what is normaly used, will not gain you anything.



Why then LED light manufacturers dont use FR4 PCB boards but lets say at least MCPCB? It means that these claims and pics from this company are false?
http://www.bergquistcompany.com/thermal_substrates/LEDs/temp-effect.html


----------



## space (Dec 5, 2009)

saabluster said:


> You've got things backwards. It gets more and more important to have high performance materials the closer to the LED die you get.



I very aware of this, but close to the LED die here, for me actually means LED die to substrate/solder point which is set with the design of the LED, which we can't do anything about. 
Thermal resistance is stated as "as low as 9C/W" for XP-e.
What is the thermal resistance for a "normal" MCPCB? Maybe 1C/W?
And the thermal resistance of the heat sink? 0,5-100C/W? Decided by the heat sink.
(Have skipped the thermal resistance from substrate/solder point to MCPCB and MCPCB to heatsink.)

So removing the thermal resistance from the MCPCB all together (when using a heat sink with no thermal resistance), one can theoretically only improve things ~10% at the max. (given a normal MCPCB with a 1C/W figure)

Choice of heat sink has the possibility of influencing the total thermal resistance a lot more.


space


----------



## space (Dec 5, 2009)

RobEU said:


> Why then LED light manufacturers dont use FR4 PCB boards but lets say at least MCPCB? It means that these claims and pics from this company are false?
> http://www.bergquistcompany.com/thermal_substrates/LEDs/temp-effect.html



When I say "...normally used..." I already mean MCPCB, or FR4 with a lot of small vias as suggested with the Rebel.

space


----------



## saabluster (Dec 5, 2009)

space said:


> I very aware of this, but close to the LED die here, for me actually means LED die to substrate/solder point which is set with the design of the LED, which we can't do anything about.
> Thermal resistance is stated as "as low as 9C/W" for XP-e.
> What is the thermal resistance for a "normal" MCPCB? Maybe 1C/W?
> And the thermal resistance of the heat sink? 0,5-100C/W? Decided by the heat sink.
> ...


I'm sorry but you are wrong. I have made prototype heatsinks out of plastic that are small but can shed the full heat load of the LED in the DEFT without raising the die temps over spec. In case you don't know I run those LEDs way over spec as far as current is concerned. Just about everyone here would say it could not be done but I have the results sitting in front of me. I don't work in a world of theory. I test.


----------



## space (Dec 6, 2009)

saabluster said:


> I'm sorry but you are wrong. I have made prototype heatsinks out of plastic that are small but can shed the full heat load of the LED in the DEFT without raising the die temps over spec. In case you don't know I run those LEDs way over spec as far as current is concerned. Just about everyone here would say it could not be done but I have the results sitting in front of me. I don't work in a world of theory. I test.



I'm quite aware of your work from reading your most often very interesting posts on this forum. As you are running your LED way over spec, the higher energy density of course benefits a lot more from a highly effective heat spreader (you are using solid copper ones right?). But for the application described as the target for the starter of this thread, I believe it will make a lot less impact.

When theory and practice don't cohere, it is often due to lack of understanding of the theory, and/or to much simplification of the theory. Energy/heat flow and there by temperatures is not the easiest to predict, and empiric testing will often be faster and/or at least a lot more correct in finding the end result than simulation in many situations. At least when one don't work with this every day.


space


----------



## RobEU (Dec 7, 2009)

Got some additional info on this graphite PCB:



​


----------

