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Applying a thermal interface material between the processor core and the heatsink surface will optimize heat transfer, even with a perfectly flat cooler that has undergone the lapping process. Most coolers included with preconfigured OEM systems feature a rubbery synthetic thermal pad in between the heatsink and the processor. Several aftermarket retail coolers also use this thermal pad because it is less expensive than the better solutions.
Thermal paste is preferable to a thermal pad. Remove any existing heatsink pad before you apply the paste. Removal of the rubbery substance should be attempted with a plastic scraper only. The edge of an old plastic credit card usually does the trick, as the card offers a good combination of flexibility and rigidity. Harder scraping implements, such as a razor blade, might scratch the heatsink's base contact surface, no matter how careful you are. Alcohol will remove any remaining deposits.
Thermal paste is the preferred thermal interface material because this thin liquidlike substance works well to fill small voids between the processor and heatsink surfaces. Silicon-based and zinc-oxide-based pastes are the most commonly available materials, offering good heat transfer at low cost. Silver-bearing pastes, such as Arctic Silver™ (http://www.arcticsilver.com), are rapidly emerging as the best choice for overclocking because they are efficient for the widest range of processors.
Good-quality silver paste can offer thermal conductivity upwards of 9 watts per meter Kelvin, compared to 0.7 watts per meter Kelvin for traditional pastes. Silver has two negative properties. It can become electrically conductive under extreme pressure, such as that between the processor and heatsink. While this is not normally a concern, you must take great care when applying the paste. Silver-based pastes also cost two or three times as much as standard thermal paste products. Considering that only a small amount of paste is needed for each cooler installation, the cost factor is not a serious barrier.
Application of the thermal paste is a relatively straightforward process, assuming you observe a few simple guidelines:
The paste should be applied to the processor core, not the heatsink's base, in a fresh installation.
Apply only enough paste to barely obscure the color of the processor core. A thick layer of paste acts as a thermal insulator instead of a thermal capacitor. The paste should be spread as evenly as possible to ensure proper surface contact.
Use an edge of plastic or other synthetic material to apply the paste; oils found in human skin can break down or disrupt the polymers in thermal paste.
These instructions can be disregarded if the heatsink comes with the paste already applied.
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