Question 1

Does it make a difference whether you apply this to the CPU or to the contact surface of the heatsink?

Accepted Answer

Short answer: No, apply it to whichever surface is smaller, and only as much as is necessary to cover the entire smaller surface (usually the heat spreader on the CPU die)

Longer:  
Text is horrible for communications, and I'm terrible at conveying tone over text, so don't read this in a negative voice, but rather as a friendly teacher voice. Trust me, It will sound so much different in your head!

Thermal grease really isn't complicated. The problem its solving is one of flatness. Despite your finger/fingernail not being able to detect surface roughness and deviations, they are there. You can buy a chemical dye that will scratch off, apply it to both sides, rub them together, and most of the dye will be left on there! Getting the two surfaces flat enough to have no air gap is quite costly.(form, lap, anneal, lap)  Instead, we just fill the gap with a liquid, albeit a very high viscosity one (grease), one that is very thermally conductive, and one that is as non-electrically conductive as possible. That's really all there is to it in a nutshell. This stuff is more costly because it is better in all those categories :)

So since the grease has no idea which side its applied to and its going to take up the space no matter what, the only concern is over application. Applying it to the smaller face helps prevent that. The other thing you have to do to prevent it is just not put too much on there (youtube can help there). Lastly, if despite your best efforts, there is still too much on there, just wipe it away! I have personally accidentally left it on there with no issue for a few years, so the stuff isn't that dangerous. Despite my accidental experiment, its best to not leave excess sitting around as it will attract and grab dust and moisture from the air. This may possibly turn the stuff conductive, acidic, caustic, and/or corrosive in some way. (eventually causing failure). Just wipe away the excess and you'll be fine

That should more than answer your question! :)

Question 2

What material is this made out of?

Accepted Answer

DONNO but according to MaximumPC & their test's this is the best on the MKT. I have been using it for 3 years or longer and the only other thing I would use would be the IC Diamond.

Question 3

Is it RoHS compatible?

Accepted Answer

Yes, it is listed on the Tuniq website as being RoHS compliant, as is the TX-2 and -3

Brand	Tuniq
Model	TX-4

Volume / Net Weight	3.0g
Thermal Conductivity	6.53 W/mK
Long Term Operating Temperature	-45 to 160 C
Specifications	Appearance: Grey Viscosity: 66,200 CP Thermal conductivity: 6.53 W/mK Operating temperature: -45°C ~ 160°C Volume: 1ml

Tuniq TX-4 Extreme Performance and Exceptional Reliability Thermal Compound

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Item#: N82E16835154012