The finger is usually pointed at the CPU (Cell) and GPU (RSX) as far as YLoDs go but the handful of PS3s I've repaired had overheating issues due to only the RSX. Problems with any number of parts can cause a YLoD but it seems 9/10 it's the RSX. The cooling for it is simply inadequate for it to last years... the 90nm ones at least.
If you simply toss your PS3's motherboard into an oven or fix it directly with a heatgun it's going to most likely go YLoD on you again. Use rosin flux on the parts before heating up the mobo. Look up anything you don't know or understand, there are thorough guides out there.
Overall you don't need much:
- Tools to take apart the PS3
- Cleaning agent (plain isopropyl alcohol will work but Arctic's cleaning compound works 10x better)
- Thermal compound (AS5 can be found at any computer shop)
- Rosin flux
- An oven or heat gun
- Common sense