Thermal paste or Liquid Metal for my gpu?

Excuse my non native Eng, but what does TIM mean :-)

If i get it right, you don't agree on using LMetal, but u are ok for using 5mm Thermal Pads, did i understand correctly?

@genik - Sorry, I should have been clearer,

TIM = Thermal Interface Material

Liquid Metal is a different kind of paste, it is not intended to gap a space. Pastes are intended to be squeezed between the given chip and the heatsink, it basically fills the micro voids of both surfaces so more heat can be transferred across when the two surfaces are pressed touching each other.

Pad’s are a filler to again transfer the heat but as the surfaces are not directly touching need to fill a void. They tend not to be as effective as a paste or even some TIM sheets which are very thin. So far pastes are the better for touching surfaces.

Pad’s are tricky! As over time they shrink a bit (hence why you need a slightly larger piece to cover the chip).

Even with the best of setups of transferring the heat between the chips to the heat sink, the dumping of heat is the bigger issue! The fan’s speed to transfer the heat into the air stream and how clean the fan blades and the heat transfer fins are become the gating factor.

Think it this way you have a stream of water filling a small tank at some point the tank becomes full and unlike our example here there is no place to spill the heat over the tanks wall, so the current heat prevents new heat to enter into the heat sink. So getting back into our model this tank needs a hole in it for the water to spill out of the size of the whole then sets the limit of the tank before it over flows. Which once again can’t happen in a heat sink setup. So we either need to enlarge the hole or forcefully drain the water (heat here) we can’t alter the heat sink, but we can force more heat out.

@danj so to cut things short... plz correct me if im wrong... your suggestion is, neither to use LMetal nor Thermal pads. Just use a good Thermal Paste in both GPU chip and Ram chips?

@genik - No on Liquid Metal as the iMac logic board running horizontal will allow it to drip.

The CPU and GPU chips (the big boys) use a good thermal paste.

The GPU board also holds VRAM chips that are near the GPU chip. These are at a different elevation from the GPU chip as such standard thermal pastes won’t work! You need a gapping paste or what I think is the better is a physical thermal pad. You need to cut the pad material up so each VRAM chip has its own and you want the pad to be a bit larger than the chip.

“Pads are used for manufacturing expedience.“ Not always, Pads are often used when the profile of the chips are at different heights to the heatsink.

The heat dissipation between the devices also needs to be considered. This gets into the natural flows of heat and just like water we take the least obstructed pathway. Here the hotter GPU chip could dump to much heat quickly into the VRAM chips before the heatsink had enough time to shed the heat buildup off the primary heatsink block

By there nature pads are less efficient that paste as the thickness of the material gets in the way of good transference of the heat. Whereas paste when properly applied fills in the pores of the two surfaces and mostly squished out leaving a few microns of thickness and as the material is also highly effective in heat transfer it’s the ideal material.

It all comes down to using the correct material!