Thermal Interface Material (TIM) application guide
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Thermal Paste Application

There is a very good article over at http://benchmarkreviews.com. To summarize, here's the main points:

  • CPU Cooling products which operate below the ambient room temperature (some Peltier and Thermo-electric coolers for example) should not use silicon-based materials because condensation may occur and accelerate compound separation.
  • All "white" style TIM's exhibit compound breakdown over time due to their thin viscosity and ceramic base (usually beryllium oxide, aluminium nitride and oxide, zinc oxide, and silicon dioxide).  These interface materials should not be used from older "stale" stock without first mixing the material very well.
  • Thicker carbon and metal-based TIM's may benefit from several thermal cycles to establish a "cure" period which allows expanding and contracting surfaces to smooth out any inconsistencies and further level the material.
  • Under perfect conditions the contact surfaces between the processor and cooler would be perfectly flat and not contain any microscopic pits, which would allow direct contact without the need for Thermal Interface Material.  But since we don't have perfectly flat surfaces, Thermal Material must fill the tiny imperfections.
  • The greater the contact pressure between elements, the better the contact conductance which will allow the thermal transfer of heat energy to occur.
  • Generally speaking, you do not want an excessive amount of pressure onto the processor as damage may result.
  • ...science teaches us that a smooth flat mating surface is the most ideal for CPU coolers.
  • It is critically important to remove the presence of air from between the surfaces, and that using only enough Thermal Interface Material to fill-in the rough surface pits is going to provide the best results.  In a perfect environment, your processor would mate together with the cooler and compress metal on metal with no thermal paste at all; but we don't live in perfect world and current manufacturing technology cannot provide for this ideal environment.
  • Silver is the best heat conductor on the periodic table of elements. Copper is #2, Gold is #3, Aluminum #4, Iron is #25. Copper is also 1.7 times more conductive than Aluminum.
  • OCZ Freeze is slightly better than Arctic Silver 5 as a thermal paste.
  • Keep in mind that thermal paste is only meant to fill the gaps, not coat the surface; perfectly flat metal on metal with no material in-between is your ultimate goal.
  • ...a single round drop of thermal paste roughly half the size of a BB is more than sufficient to cover the entire mating surface of a stock Intel-included cooler.
  • 2 parallel lines of TIM running perpendicular to the grains on the surface(s) spaced apart at 1/3 processor width is ideal for square heatsinks.