How do I mount heat sync with thermal compound?

Working on iBooks G4 I always used the same pads when they were not damaged. Never had heat issue with the units I repaired. If Apple used thermal pads, there must be a good reason. In fact I never seen a ibook with thermal paste, always thermal pads. Maybe it's because of a bigger gap between the processor top and the heatsink ??? If you decide to use the thermal paste put it a good amount to be sure the gap will be filled. Also, a good advice is: do not put too much pressure on the two heatsink nuts (with springs) when installing the heatsink to the board. The screws are fixed in solder pads under the logic board and it easy to desolder them if you torque them too much. You then have to solder them back to the board.