3.4 Preparing the Motherboard for Installation
3.4.5 Installing the heat sink and fan
Most microprocessors will produce a lot of heat, which if not efficiently dissipated can cause the system to operate intermittently or fail completely. One way to dissipate heat from processors is to use the heat sink and cooling fan. Proper installation is crucial to this unit performing its role effectively. Although the heat sink can be mounted before installing the processor chip on the motherboard, there is a risk of causing damage to the pins on the chip. Only on Pentium II processors is the fan attached before the CPU installation.

The following step-by-step applies to socket 7 and other socket type processors:

Step 1 If the CPU fan did not come with the heat sink already attached to it (in most cases, it will be attached), use the screws that came with the fan to attach it to the heat sink. 
Step 2 Apply the heat sink compound to the surface of the chip. Some setups use heat sink compound or thermal grease. Apply a thin layer, just enough to cover the surface of the chip. In practice, the heat sink compound in some of the setups where clips are used to hold the heat sink down may be skipped, but bear in mind that using the compound is still a good idea. The heat sink compound or thermal grease improves contact between the CPU surface and the heat sink, thereby permitting better heat dissipation. 
Step 3 Now attach the heat sink. Proceed with care at this point. Place the heat sink squarely on top of the processor, and press it down gently. Most of the newer heat sinks actually use a set of clips on each side to hold them down. A little force may have to be used to bend the clip in place. In fact, if the orientation is not right, the clips will be quite challenging to bend down into the right position. Sometimes it takes a few trials to get the right orientation (this is especially true for the new AMD socket A). In other cases, the heat sink simply wraps around the processor with the heat sink compound being the only real attachment. 
Step 4 At this point, double-check to make sure the heat sink maintains a good contact with the processor chip surface. Usually when the heat sink is inserted backwards, the chip surface and heat sink become staggered. If this happens, remove the heat sink, turn it around, and try to reattach it. 
Step 5 Some heat sink compound or thermal grease may have oozed out the sides of the contact surfaces when the heat sink was pressed down. Wipe up the excess compound. 
Step 6 Plug the power cord from the fan to the fan power pins provided on the motherboard. Make sure to observe the proper orientation.

Processors that come with the fan and heat sink already attached to them are more convenient. These are called boxed processors. Boxed processors cost a bit more but are safer to install since it lessens the chance of breaking the pins. The above steps can then be skipped. They also have better warranty coverage than those without the fan and heat sink attached.