General Copper Mod Question

I have removed the thermal pad from my GPU and would like to carry out a copper mod to reduce my temperatures. The GPU die measures 9mm X 9mm and the copper heat sink pad measures 15mm X 15mm. I have checked the thickness required as 0.9mm. My question is do I order a shim slightly larger than the GPU die say 10mm X 10mm or slightly smaller that the copper heat sink pad say 14mm X 14mm. Has anyone carried out any tests to establish which is better/more efficient for heat transfer/cooling. Could someone advise as I have my laptop in bits and would like to order the correct size shim asap. A further observation is that there are some surface mounted components around the perimeter of the GPU die, I am assuming that they are lower than the face of the die, would there be a risk of shorting these components if a lager shim is advised?

 

The shim should not interface with any other surface except the GPU Chip and the thermal assembly that said if possible make it as large as possible so more heat can be absorbed.

 

Thanks for the super quick reply. Looks like the prefered choice is 14mm X 14mm then.

 

Metal doesn't really absorb heat... physically speaking that's ehm - nonsense.

However the idea that a larger area is beneficial to heat (or to be specific energy) transfer is correct.

By the way - there are "liquid metal pads" that you can use for CPUs, that should work with a GPU too.

Also - you'd need optimum contact if you have a solid plate - no air bubbles - that's why thermal pastes are used so often.

 

Thanks for the feedback, i was hoping it would attract more response/comments. Still looks like the larger shim will be best then. Basicaly I want to get it right first time, I dont want to be having to take the laptop apart again. I would like to keep on topic (meaning the size of the shim) but for the record I shall be using ICD7 paste.

 

Well, if you also use thermal paste then you should have a "large contact area" - i.e. no potential gaps or air traps - which is good

Good luck!

 

Increase mass = increase heat capacity

 

heat capacity has nothing to do with thermal conductivity.

 

True - but overall heat capacity alone doesn't affect heat transfer.

If you wanted heat capacity - there are many materials with a higher heat capacity - or rather energy capacity than metals - and copper is pretty low too.

 

Thanks for the comments but I think you are missing the point, possibly me not explaining correctly. Basically I have a choice of ordering a small surface area shim 10mm X 10mm (approx 3/8ths square) or a larger surface area shim 14mm X 14mm (approx 9/16ths square). The surface area of the GPU die (the heat generating bit) is only 9mm X 9mm (approx 5/16ths square) The gap between the GPU and the surface of the heat sink is approx 0.9 mm (originaly filled by a thermal pad, yuk!) so is it best to fill this gap with the smaller surface area shim or is there any real advantage in using a larger surface area shim bearing in mind that the larger area shim will only be in contact with the small surface area of the GPU die. Hope that makes sense.

 

Large area would be better for passing off heat to the heatsink - that's why fans have those "thin plates" for the cooling system.

 

No you need something with high conductivity to transfer energy to the fan a metal with high heat capacity is a bonus.

 

It only helps when the heat sink is not copper. So the copper sheet can help heat spread on transverse direction. But large sheet shouldn't hurt either.

 

Not so,
the area of the copper shim should be the same size as the die. Simply measure the dimensions of the die which comes into contact with the heatsink. You want to stay to those dimensions. If you go larger, yes you have more mass, but it does not equal faster thermal conduction. A smaller shim, one the size of the die results in maximum cooling efficiency. You are right in that more surface area = better cooling, as in more surface area for air to come in contact with, but that is irrelevant when talking about the interface between the processor and the heatsink

Detlev, metal does retain heat. If your statement were true, an automobile engine would not be hot just after it were shut off.

K-TRON

 

Thanks guys for all the interesting feedback.
I think I will go with K-TRON’s logic and order a shim the same size as the GPU die. Also, as an added bonus, I would not have to worry about the possibility of a larger shim touching the surface mounted components around the perimeter of the GPU die.
Thanks again.

 

Why not just use thermal paste..?

 

He said that the gap is 0.9mm thick
Look at that on a ruler, and you will see that thermal paste simply will not do.
Thermal paste is about 0.05mm thick. It cannot be the sole medium when replacing thermal pads.

K-TRON