I have removed the thermal pad from my laptop 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. Basicaly I have a choice of ordering a small surface area shim 10mm X 10mm or a larger surface area shim 14mm X 14mm. As mentioned above the surface area of the GPU die (the heat generating bit) is only 9mm X 9mm. The gap between the GPU and the surface of the heat sink is approx 0.9 mm (originally 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. Has anyone carried out any tests to establish which size 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 but would there be a risk of short circuiting these components if a lager shim is advised?
Technically, using the larger area shim would allow you to transfer more heat, but I don't think the change will be significant. You need to be careful not to short out any components (as you said) so it's a judgment call on your part.
Be advised in addition to the shim, you will need to install some thermal paste on both sides of the shim, so that you get maximum heat transfer from the GPU to the plate and again from the plate to the heatsink.