What does a coldplate do?

[Ruahrc]

I'm kinda lost- from what I take, a coldplate is simply a piece of metal (usually copper?) that you stick between your heat producer (peltier, cpu, video card) and your cooling unit (HSF, Water Block).

What I can't figure out is what it actually does. I mean I can kind of see putting a copper coldplate on an Al cooler unit to improve heat removal from the cpu/whatever, but in doing so you add a layer of "contact" which you have to use paste to complete- thus you possibly decrease the thermal connection creating worse results.

Am I missing something? Please explain the use of a coldplate and tell me if I needed to have one (WC system, no peltier or anything like that)

Thanks

Ruahrc

[krusty the klown]

Cold plates are primarily used in peltier systems.

They are ideally silver, several mm (3-5) thick and have the same surface area as the peltier. They sit between the CPU and the cold side of the peltier.

The reason for using one is to do with the construction of a peltier and the thermal properties of the ceramic-type material that the peltier is made of.

Peltiers are an array of individual elements. Most modern CPUs are of the flip-chip variety with tiny exposed cores. If you applied a peltier to, say a flip-chip P3, the only elements that are cooling the CPU are those directly above the CPU core. Those elements outside this area are simply cooling air, as the ceramic cannot efficiently transfer the heat of the CPU to these outside elements.

By placing a thick plate of conductive metal between the CPU and the peltier, all the individual elements in the peltier are now thermally coupled to the CPU.

Imagine this - I have a 70Watt peltier and I'm trying to cool a 40W CPU. Should be fine?? Well, if I do not have a cold plate, then...

Peltier = 4cm*4cm = 16 cm^2

Cooling capacity = 70W => 4.3W/cm^2

Approx. area of CPU core = 1cm^2.

Heat output = 40W/cm^2 => one dead CPU http://www.sysopt.com/forum/frown.gif

If the surface area of the object you're trying to cool is the same as that of the peltier, then there's nothing to be gained by using a cold plate. Similarly, if I was using a 16cm^2 water block to cool the hot side of my 16cm^2 peltier, then there's nothing to be gained by using a 'hot plate'.

Water blocks are made of metal anyway, so if you're just using the water system to cool the CPU & there's no peltier involved, then there's little (if anything) to be gained by using a cold plate.

Probably the best thing to do, if you're looking to improve cooling performance, is to lap your water block, if you haven't already done so.

Hope this helps http://www.sysopt.com/forum/smile.gif

[Ruahrc]

Krusty- thanks for clearing that up. Makes a lot of sense now. My waterblock is lapped and polished- looks like a dirty mirror on the back.

By the way this is my "official" post #501, apparently replying to yourself right away doesn't count.
http://www.sysopt.com/forum/Forum17/HTML/003859.html

Ruahrc

[krusty the klown]

Nah, posts in community don't add to your post counts http://www.sysopt.com/forum/smile.gif

Glad to help http://www.sysopt.com/forum/smile.gif http://www.sysopt.com/forum/smile.gif