PS3 Yellow light of death, Do I need a heat gun?

@imlance you should use a heatgun. A hairdryer does not provide enough heat for any solder to liquify (but sometimes it helps to close the gap between the solder bumps and the die. Read more in the latter part of this answer). You can check for a comparison between the two Hair dryer for logic board reflow? First you do need to remember that this will only work if your YLOD is caused by solder fractures and if they are not to extreme. Reflowing any board with a heatgun is not an exact science and as such does have a certain amount of failure. The proper fix for this would most likely be a professional reball with a new IC (unlikely you can find one. Anyhow, the biggest reason for failure to reflow is not enough consistent heat. There is a fine line between reflowing and absolutely melting the solder, so one needs to be aggressive without going over board. If nothing else, get a couple of temperature probes and see what heat you generate. You also need to make sure that you apply the thermal paste properly etc. Follow the guide from here and keep on trying.

Second remember that there can be multiple causes for the YLOD:

Dead/Disconnected BluRay Drive

Cold-Joint between the CPU/RSX/EE(If your console has one)

Failing Power Supply

Overheating

Corrupted NAND Flash, and multiple others. the use of this may work for a short time but the real reason for this is the design of the IC. It is a flip Chip design which has shown multiple failures for the PS3 as well as Xbox360 which uses the same design for their IC. Here is a very "quick and dirty" explanation of what causes most of the RROD. It is not always a failure of the solder balls which connect the Flip Chip BGA package to the motherboard. It does happen and you can see why [ http://www.bunniestudios.com/blog/?p=223|on here] More commonly however is that the failure is due to the chip design itself.

As you can see the "bumps" are what actually connects the die to the substrate to make the chip complete. If these bumps fail, the die does no longer make contact with the substrate and thus no contact with the circuit board. The chip has failed.

So what happens is that the chip heats up (due to poor design of the ventilation and heatsinks of the console. Does not matter if it is a PS3, a XBox or some of the Mac laptop's) and the bumps that connect the chip to the substrate lose contact and your chip (in this case processsor) fails. The heating of the chip for the reflow actually reshapes (most of the time) the bumps to the point of making contact again. That is the reason why some reflows just do not work. The connection between the IC and the substrate has absolutely failed. In those cases you will need a new processor. Not the most scientific explanation but I hope it makes sense to you.