Today’s processors are running quite hot. Advancements are being made to make them run cooler at higher speeds, but the importance of a high quality heat sink and fan cannot be overstated. PCs that are not properly cooled can be quite unstable, or at its worse, it may not even boot properly.

It used to be that you could attach a heat sink and fan to your processor directly and not worry about it. Today, though, processors run too hot to do this and expect a reliable PC. One must use heat sink compound to seal the gap between the heat sink and the top of the processor.

Some heat sinks have a rubber heat pad on the bottom of them. In these cases, you don’t really need to use heat sink compound because the rubber pad will create the seal. It should be kept in mind, though, that if you are using a heat sink which has been used before and had a heat pad, that heat pad is now likely melted in the spot where the previous processor contacted it. In these cases, you cannot use the heat pad again as it will be ineffective. Instead, you need to clean the old rubber pad off of the heat sink using a non-abrasive cleaning compound. Many people use isopropyl alcohol and a broken old credit card to scrape the rubber off without damaging the heat sink. When the pad is removed, you can use the heat sink again using heat sink compound.

1. Attach the fan to the heat sink. This step is almost always already done for you, but if not, you must do it yourself. This is done using the four screws that came with the CPU fan.
2. Clean the top of the processor. Using a lint-free cloth and isopropyl alcohol (or some other non-abrasive cleaning solution), ensure that the surface of the processor is clean and free of dust and finger oil. Do the same to the bottom of the heat sink. Pay attention to the note above on heat pads if your heat sink had or has a rubber heat pad.
3. If you are using a cooling shim, place it onto the top of the processor now. Not all processors require shims. In fact, no processors require shims; they are completely optional. But, some people like to use them because they help to increase the surface area of the top of the ship and spread the weight around evenly. See, some processors (such as the Athlon XP) actually have the core sticking up slightly from the rest of the processor. So, when the heat sink is placed on top, all of its weight comes down on the core. If the fan is a real tight fit for the motherboard, it could really create a weight load on the processor core, and some people have actually crushed their CPU core by accident. A shim is simply a thin piece of metal, especially designed for a particular processor, which fits over the processor and evens out the height and helps to alleviate the crushed core problem. When installing a shim, be extra sure you are aligning it correctly. They often have holes in them exactly placed so that the cache bridges on top of the processor can poke through. If the shim is not properly aligned, you could short out these bridges and actually burn out your processor if you run your PC that way. Additionally, a mis-aligned shim could cause the heat sink to not actually have full content with the CPU core, leading to overheating.
4. Apply the Heat Sink Compound. Assuming you are not using a heat pad on your heat sink, apply a very thin layer of heat sink compound to the top of the processor core. If, as is the case with Pentium IV processors, the top of the processor is totally flat, then apply the compound to the entire top surface of the processor. Many heat sinks come with heat sink compound in a small little package, usually just enough for a one-time install. You can pick up better quality compound online. Arctic Silver is a very popular choice. Be careful not to get compound on any motherboard electronics. Apply only a very small portion to the processor. Only a very thin layer is required. The compound must be spread out evenly across the top of the chip, forming that very thin layer. When spreading the heat sink compound, do not use your finger. Use the edge of a credit card, or you can use a rubber glove or even just a plastic bag over your hand. Do not apply any heat sink compound if you plan to use a heat pad.
5. Attach The Heat Sink. Place the heat sink/fan combo squarely on top of the processor, pressing down lightly. Do not do any twisting as you install the heat sink. Press down firmly, but straight down so as to preserve the heat sink compound layer you just applied.
6. Secure the heat sink. Most newer heat sinks use a set of clips on each side to fasten itself down. These clips attach to a pair of tabs on each side of the socket. It will probably take a little bit of force to bend the clip down over the tab. Other heat sinks wrap around the processor, then just sit on top, the compound being the only real attachment. Pentium IV motherboards have a heat sink retention bracket around the processor socket. When you install the P4 heat sink, you will fasten each of the four retention clips into the retention bracket and then close the clip levers on top of the heat sink to fasten the heat sink down onto the Pentium IV processor.
7. Double-Check. No compound should have oozed out from the sides. If it did then you applied too much and need to remove the HSF, clean both the heatsink and CPU and start over.
8. Attach fan to power source. Unless your CPU fan is powered via a standard power supply plug, it is probably powered by a wire attached to a 3-pin power lead on the motherboard itself. You can attach this now. The CPU_FAN power lead is located near the CPU interface somewhere. The lead will have two small pins on each side, and these pins surround the power plug and the pins are inserted into the holes in the plug. It should be pretty easy and obvious.