Step 3: Now spread this over the core using your finger with a plastic glove on or any appropriate device to avoid having oils from your finger contaminate the thermal compound giving you less transfer of heat. You will want a very thin layer because you will also be applying thermal compound to the base of the heatsink.
Using a good heatsink is vital in keeping your CPU as cold as possible with air cooling ( duh! ). It is always wise to lap your core and your heatsink base to get the best contact but with your heatsink. If you plan on overclocking you should take lapping into consideration.
Step 4: Just like the CPU, you will want to clean the base of the heatsink with rubbing alcohol. Remember to use a lint free cloth (old t-shirt) so you don't get lint on it.
Step 5: You now will apply a fair amount of thermal compound and rub it over the base with your finger. It is hard to see the artic silver in the next picture because it is silver, and the heatsink is silver (in color)...!!
Step 6: After you have a fair amount on there you will want to scrape off the excess ( most of it ) with a razor blade. This is very important. Thermal compound is used to fill in the gaps left on the base of the heatsink and on the core of the processor done by machining. This garranttees a smooth contact area.
As you can see there is very little left on the heatsink, as it should be.
Heres a picture of just how much thermal compound came off with the razor (most of it!)