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 side should be the same.
The oblique view shows how close the bold heads come to the heatsink. However, the bolt heads and steel washers do not make contact with the heatsink. It is important to permit the springs to exert the contact force. Tightening to bolts too far will crush the northbridge and may destroy your PCB.
Don't forget to reconnect the temperature sensor wire.