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Old 11-13-2010, 04:13 AM #1
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Default Will this have sufficient heatsinking?

Hi, I was wondering if this "S" design would heatsink a driver enough.
I thought since there is a lot of surface contact between the copper and host it would be ok, but then i thought maybe not because it is just a thin sheet of copper and i always see builds with big heavy heatsinks.





And this next one is easier to do but i dont know how it will be since there is a lot of thermal compound needed to fill in the gap. ( this stuff http://www.canadacomputers.com/produ...item_id=021295 if it matters)



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Old 11-13-2010, 08:22 AM #2
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Default Re: Will this have sufficient heatsinking?

In a word, no. It will be better than having just air around your diode, but will not function as a good heatsink.

Let's put things into perspective. Solder (lead/tin) has conductivity of around 40W/mK, brass around 109W/mK, and pure aluminum has around 257W/mK. More expensive materials like copper, diamond, silver, etc. will have even better conductivities (350+). The best thermal compounds such as Arctic Silver have thermal conductivity ratings of about 8-9W/(mK). Why? Because despite having silver in it, thermal compounds are only effective for transferring heat in extremely thin layers (< 0.025mm). In those extremely thin layers the conductivity goes up to about 350W/mK because the silver particles are directly between the heatsink and its heat source. Thus the thermal compound is only useful for filling in the gaps between the heatsink and your heat source. It's there to fill in for the air gaps that may be present between the two surfaces which would be far worse than having thermal grease. Even if you could just pour Arctic Silver into a mold as your heatsink, look at the price: 12 grams for $17 on the site you've linked. You'd need many tubes just to fill in the space in your host, and for that price you might as well buy a custom heatsink instead.

Speaking of filling gaps, your layers of copper sheets will have air gaps between them, which will prevent good transfer of heat between the diode and the outside. You will want a solid mass of metal around your diode (a heatsink) as a way of quickly moving that heat away from the source where it can be dissipated at the surface of the heatsink (the fins). Less mass will mean the heat must be quickly dissipated away at the surface or it stays trapped in the device.

I would just buy a pre-made heatsink for your laser and save yourself the hassle and cost.

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Old 11-13-2010, 09:51 AM #3
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Default Re: Will this have sufficient heatsinking?

There are specially designed "fillers" for transfer heat, but i doubt they can be found in "hobbyst size" ..... they are used industrially ..... as example, this company produce them, they call it "gap filler" ..... they have also a "sample request" page, but i don't know if they sell to privates .....
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Old 11-13-2010, 01:06 PM #4
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Default Re: Will this have sufficient heatsinking?

Quote:
Originally Posted by Bionic-Badger View Post
In a word, no. It will be better than having just air around your diode, but will not function as a good heatsink.

Let's put things into perspective. Solder (lead/tin) has conductivity of around 40W/mK, brass around 109W/mK, and pure aluminum has around 257W/mK. More expensive materials like copper, diamond, silver, etc. will have even better conductivities (350+). The best thermal compounds such as Arctic Silver have thermal conductivity ratings of about 8-9W/(mK). Why? Because despite having silver in it, thermal compounds are only effective for transferring heat in extremely thin layers (< 0.025mm). In those extremely thin layers the conductivity goes up to about 350W/mK because the silver particles are directly between the heatsink and its heat source. Thus the thermal compound is only useful for filling in the gaps between the heatsink and your heat source. It's there to fill in for the air gaps that may be present between the two surfaces which would be far worse than having thermal grease. Even if you could just pour Arctic Silver into a mold as your heatsink, look at the price: 12 grams for $17 on the site you've linked. You'd need many tubes just to fill in the space in your host, and for that price you might as well buy a custom heatsink instead.

Speaking of filling gaps, your layers of copper sheets will have air gaps between them, which will prevent good transfer of heat between the diode and the outside. You will want a solid mass of metal around your diode (a heatsink) as a way of quickly moving that heat away from the source where it can be dissipated at the surface of the heatsink (the fins). Less mass will mean the heat must be quickly dissipated away at the surface or it stays trapped in the device.

I would just buy a pre-made heatsink for your laser and save yourself the hassle and cost.
OK. so the 2nd picture definitely wont work. But how about the first one? In that first one i wouldn't be using the compound as a filler, i would just be using a thin layer (how its actually meant to be used) to stick the copper to the host, that way the host would be the heatsink. I just thought it didnt matter how thick the copper was since it isnt going to be acting as my heatsink it is just going to be used to transfer the heat TO the heatsink (the host)
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Old 11-13-2010, 02:18 PM #5
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Default Re: Will this have sufficient heatsinking?

just a doubt ..... why you don't just take a rod of copper or aluminium, same diameter of the inside of the host, and cut it for the long, obtaining 2 semicilinders ? (like the green part in your second draw) ..... this may be the better solution for all the possibilities ..... mechanically resistant, heath conductive and efficent ..... then use the thermal compound for glue it on the host and for glue the driver on it, and you're ok .....

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Will this have sufficient heatsinking?-halfrodheatsink.jpg  
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Old 11-13-2010, 04:27 PM #6
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Default Re: Will this have sufficient heatsinking?

The thickness of the sheet definitely matters. Even over the short distance to the host, a thin sheet of copper will be a large thermal resistance to overcome.

If you have sheet material thats a milimeter or so thick, it would work fine as long as it has good contact on the edges. You could get a piece of copper pipe that is the interior dimension of the host, and then cut it along its length (using a dremel or something). Now you can bend part of it flat, such that you have a good contact surface to the host, and a fairly tick piece of sheet to mount the driver on.
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Old 11-13-2010, 11:24 PM #7
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Default Re: Will this have sufficient heatsinking?

Quote:
Originally Posted by HIMNL9 View Post
There are specially designed "fillers" for transfer heat, but i doubt they can be found in "hobbyst size" ..... they are used industrially ..... as example, this company produce them, they call it "gap filler" ..... they have also a "sample request" page, but i don't know if they sell to privates .....
Those have the same or worse performance than the Arctic Silver. The gap filler only has conductance on the order of 3-4W/mK, whereas the pads are 8-9W/mK. That's fine for attaching your mosfets to a heatsink, but is not going to be sufficient for a laser.

Quote:
Originally Posted by weidmark View Post
OK. so the 2nd picture definitely wont work. But how about the first one? In that first one i wouldn't be using the compound as a filler, i would just be using a thin layer (how its actually meant to be used) to stick the copper to the host, that way the host would be the heatsink. I just thought it didnt matter how thick the copper was since it isnt going to be acting as my heatsink it is just going to be used to transfer the heat TO the heatsink (the host)
The host will only act as your heatsink if you can transfer the heat to it efficiently. Thin copper will not do the job very well.

Look at the effective thermal conductance of the medium surrounding your device. A thin strip of copper is only a small fraction of the volume that around the device that can transfer heat out. Therefore, most of the medium around your device for transferring heat is air which is a terrible conductor.

You want to have as much conductor around your device so that heat is rapidly moved away where it can be dealt with in a more effective manner (the outside of your heatsink). A thin strip will not do the job. You'd do better to bond and mount your device to a series of copper pennies rather than deal with thin layers of copper foil. At least they're solid and somewhat thick.
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