Whether you’re building a new machine from scratch or upgrading an existing system, installing the CPU can be a tricky task. It’s like a simple, but delicate, bit of computer brain surgery. In this article, I’ll step through the process of CPU installation on a modern ATX motherboard. I’ll be using an AMD Athlon processor and Shuttle Socket A motherboard in my example, but the general process can be followed for other socket-based chips and motherboards.

Laying the patient out
If you are building a custom machine, preparing for the installation of your CPU should be fairly simple. Essentially, you’ll work on the motherboard before you place it into the case.

If you are upgrading a computer, you’ll need to remove the motherboard from the case, which involves unplugging all power and data cables and removing any PCI, ISA, and graphic cards where applicable. It may look like the CPU is easily accessible while the board is still in the case, but as you go through the installation process, having the motherboard out of the case proves well worth the effort.

You should first be aware of the potential for an electrostatic discharge (ESD), which would make the whole process of installing the CPU a moot point. Part of your preparations should include ESD prevention through a wrist strap, workbench antistatic pad, or both.

Place the motherboard on the workbench so it’s both secure and firmly backed. The work surface shouldn’t be hard or metallic. If your case allows for the motherboard backing plate to be removed, do so, because it makes a perfect base for operating on the motherboard.

Before starting the actual installation, consider the type of thermal paste/grease you will use. Thermal pastes are compounds that are placed between the CPU’s core and the heat sink, increasing the thermal conductivity between the two devices, thus giving you a cooler processor. New heat sinks usually come with either a preapplied, wax-embedded thermal paste or a small tube of ordinary thermal paste. Although these factory pastes are adequate, I recommend spending a few bucks on a premium thermal paste. I purchased a tube of Arctic Silver II thermal compound for $7.00, which provides enough to use on nearly 30 processors.

If your heat sink came with a preapplied, wax-embedded thermal paste and you’ll be using this, you can skip to the next section. If not, or if the heat sink removed from the old CPU had thermal grease on it, you will need to remove all remnants of the previously used grease from the heat sink’s bottom (see Figure A).

Figure A
Even after the grease is removed from a new heat sink, you can see remnants on the surface.

This will require more than simply wiping off the heat sink’s surface with a clean rag. The worst conductor of heat is air, so to get a good thermal seal between your heat sink’s surface and the CPU die, both surfaces must be clean and free of debris. You can assume the die on your new chip is clean since it hasn’t been out of its packaging.

What’s a die?

The CPU die is the small raised square on top of the CPU. Some Intel processors will have a heat-spreader over the die.

Artic Silver recommends that the heat sink surface be cleaned with “a xylene-based cleaner (it’s in Goof Off and some carburetor cleaners), acetone, MEK, mineral spirits, or 99 percent pure isopropyl alcohol.”

Cleaners that may leave a residue, such as heat-based products, citrus-based products, and some degreasers, should be avoided.

Once the heat sink is clean, you can proceed with the installation.

Tab A into slot A
Modern, slot-based ATX motherboards include what is called a zero insertion force (ZIF) socket. These CPU interfaces are designed so the processor can only be installed one way (see Figure B.)

Figure B
The empty ZIF socket has a release arm on one side.

The ZIF socket also has a locking lever that must be raised prior to inserting the processor that releases the socket’s pin holders. Once the arm is raised, no force should be required for the CPU to slip into the socket. If the processor doesn’t fall effortlessly into place, something is wrong. Check the processor’s alignment with the socket, and make sure the locking lever is fully raised.

With the AMD Athlon I used in this article, the top of the processor should be oriented so the corner of the processor with its point missing will line up with the base of the open locking lever on the ZIF socket. This places the corners of the chip with missing pins in the right position over the socket (see Figure C).

Figure C
With the CPU in place in the slot, it is easy to see the chip orientation to the top of the socket.

Once the chip is seated in the socket, lower the locking lever to clamp the prossesor’s pins in the socket.

Preparing the heat sink
With the CPU safely locked into its socket, it’s time to prepare the heat sink. Heat sinks are typically a block of aluminum or copper into which an array of fins has been cut. Heat is transferred from the CPU, through the metal block, and into the air through the fins.

Heat sinks are heavy for their size and can crush the CPU die if not handled correctly. Larger heat sinks often have a groove cut into one edge that aligns over the top of the ZIF socket.

Even though both the CPU die and the heat sink surface appear flat and smooth, this is not the case. The die might not be perfectly flat, and even if it were, the surface of the heat sink might not match it perfectly.

As I mentioned, thermal grease is used to match the two surfaces so air doesn’t get in between and hamper the transfer of heat from the CPU die to the heat sink.

If you are using the thermal compound that came on the bottom of your new heat sink, you can skip to the next section. Just remember to remove the paper covering the thermal compound before installing the heat sink. Otherwise, you should apply your thermal grease to the CPU die.

First, place a dab of the thermal grease on the heat sink surface and, using a razor or other straight-edged instrument, scrape some of the grease from the heat sink. Deposit it on the surface of the CPU die.

Because the machined tolerances between the two surfaces will be close, only a thin layer about the thickness of a sheet of paper needs to be applied as smoothly as possible to the CPU die surface (see Figure D).

Figure D
Apply a thin layer of thermal grease to the top of the CPU die.

Then, return to the heat sink surface and use a lint-free towel or a clean plastic bag over your finger to smear the thermal grease over the surface of the heat sink. Vigorously rub the grease into the surface in an erratic and circular motion to fill in all the pores and imperfections in the heat sink’s surface. Then, wipe off the surface to remove the excess grease.

Installing the heat sink
At this point, it is important to remember how fragile the CPU and its die are. The AMD Athlon I installed for this article came with four rubber pads on top of the chip to prevent inadvertent crushing of the CPU die. Many AMD and Intel CPUs have these pads. Whether your processor has these pads or not, special care must be taken not to damage the CPU during heat sink installation. Just remember not to push on it too hard.

This is where having the motherboard out of the box is a great benefit. Out of the box, you can properly position the heat sink above the CPU, while also ensuring that you lower it into place as level as possible.

The grove along the top edge of the heat sink should align with the top of the ZIF socket, and the heat sink attachment clips should align with the tabs on the ZIF socket.

When installing my heat sink, I sat the heat sink on the CPU so that it rested on the chip’s rubber pads and was aligned with the socket.

Next, place one hand on the heat sink to prevent it from moving, but don’t press on it with much force. Then, use a screwdriver or your finger to press on one of the attachment clips before doing the same with the clip on the other side of the heat sink. Remember to put the downward force on the clips, not on the heat sink and CPU die. If your heat sink only has a single socket attachment clip on one side and slots on the other, slide the slots over the socket first and then attach the clip using the directions detailed above.

Your heat sink is now installed (see Figure E).

Figure E
Finally, the CPU is installed and the heat sink and fan rest upon it.

The only thing left to do is connect the heat sink’s fan to your motherboard’s fan connection (if applicable) or, after the motherboard is placed in the case, to the wiring harness of the power supply. Sometimes, the heat sink manufacturer will recommend that the fan be plugged into both the motherboard and the wiring harness. When you start the computer for the first time after installing a new CPU, watch to make sure the heat sink’s fan is running. If it is, you can sit back and enjoy your new creation. If it’s not, check your cable connections and make sure the power supply is functioning correctly. If neither of these seems to be the problem, check your documentation to ensure the fan is correctly connected to the motherboard.

Have you created a monster?

Times have changed since the days you had to set voltage jumpers for CPU sockets on motherboards. The process of installing a CPU is much simpler now. Did we leave out a step or two here? Tell us what you would do differently in the discussion below.