Bolt the northbridge heatsink into place. Do not tighten until the springs are fully compressed, but make sure that the heatsink is held firmly in place. Pressure on the two sides of the heatsink should be the same.

Here you can see the clean surface of the CPU ready for pasting. The paste should be laid down in an horizontal line as viewed in this photograph, covering two-thirds of the distance from side to side of the CPU lid.