This is copied from a post I made on Playstation Communities forum:
I've been fixing PS3s and 360s for my friends whenever they get a YLOD or 3 Red rings etc.
Now for some PS3s they don't die after a few months and keep running, some will work only for a month or so and YLOD again.
Whenever a PS3 YLOD again, I redo the heat gun fix and sure enough they will come back. I've done a lot of research and I can definately see that I am not the only person having this issue with YLOD PS3s.
Now heres my procedure on how I fix:
Take the PS3 apart (can find guides on this online, do NOT do this if your PS3 is under warranty it will be voided)
Clean the GPU and CPU chips on the motherboard w/ 99.9 Alcohol (Can be found at most electronics stores)
Set the motherboard of the PS3 flat on top of a griddle board (I use a George Foreman and also a clamp to keep the board just above the griddle)
Apply no clean flux to the side of the both chips before heating
Pre heat the board from the bottom to 120 C
Slowly heat the top of the board (while being heated to the bottom) using the Heat gun (do this for 5 min)
Using a cooking thermometer (The infrared ones are ******* in my opinion have tried 2 different companies. Both times the PS3 outright fried because of inaccurate temparuture readings) set the needle on top of the first chip to be heated.
Slowly Heat up the chip using the heatgun to bring the temparature up to 220 C - 227 C and keep in that range for about 45 seconds
Do the same to the other chip
Let the board cool for about 25 min (I've read people cooling for 10 min I just do 25 min as a precaution until chips cool off to room temperature)
Apply Arctic Silver 5 PROPERLY to both chips and resassemble and test for 45 min (Run fifa cpu vs cpu etc over and over)
Although summarized, that is the exact procedure I've used to fix maybe 25 to 30 consoles. Out of those about ten will keep coming back.
The last thing to try is a method called RE-BALL (a kit needs to be purchased for this)
You can use this guide to get a more exact reflow than just "point your heatgun at your chips for 3 minutes in circular motion etc" BUT for those of you that have tried similiar methods:
What temperature ranges do you follow and for how long ?
Why use no-clean flux ? (from what I understand it helps the reflow process)
I have a few PS3s to experiment with to see if I can completely perfect this method as it can be used for more than just consoles (laptops, any pcd board depending on the material used to construct, consoles, phones, harddrive boards etc)
The method I've chose is based to mimic this machine for as cheap as possible:
I hope this helps those with failing reflow issues (i.e. ps3 doesnt work at all after reflow)
but if you have any input to make this method robust/better it would be highly appreciated.