The underside of the northbridge heat sink must also be cleaned. Use a sharp knife to scrape away the old plastic transfer tape.
Carefully smear a very small amount of thermal transfer compound (available from Electrolube, address at end of instructions). It is vital that you use the very minimum of compound. Place the heat sink back on the chip, slightly off centre and apply pressure at the same time as twisting the heat sink into position. This thins the compound even further, so that the compound does exactly what it should do, i.e. transfers heat from the chip to the heat sink If there is too much compound it tends to prevent efficient transfer. The heat sink can then be clipped back in place.

The main processor chip is held in place with a zero insertion force (ZIF) socket. Lift the arm at the side of the socket and look carefully at the pattern of holes on the socket. You will see that one corner of the socket has a pin missing. The Processor chip must be dropped into the socket, and obviously has to be orientated the correct way so that the missing pin aligns with the missing hole!
The lever on the ZIF socket can now be closed.
Surrounding the processor is a large plastic bracket that is used to hold the processor fan. Follow the instructions that come with your fan, making sure that you apply thermal transfer compound to the processor chip in a similar way to the northbridge chip. The processor chip has a larger surface area than the northbridge chip and it is harder to ensure a good fit. Take your time - this is vital.

It is good practice to use efficient cooling, and the above sequence of pictures show how a Zelman cooler can be installed. As this is not essential, I have included the instructions on how to install this cooler on a separate page, click on any of the above images to view this page.