If everything goes well, I'll document the delidding here. I just need to test the CPUs first. Any advice would be great!
I've recently delidded a bunch of CPUs for me and my friend, and it's in fact not that scary or difficult. But it takes some practice.
1. We've bought 2x X5675 and 2x X5680 for our Mac Pros, but those were hard to chase on eBay for good prices, so I've also purchased about 5 different CPUs for testing about $5 each. For example, X5550 is compatible with 4,1 tray and can be tested all the way.
2. Before delidding I've tested every CPU to make sure they are actually ok. For this you need to do the following: On a two-CPU tray remove CPU B cooler and CPU itself. Install lidded CPU into slot A. Then carefully pull fan connector from the assembly, place it over, and after that you can carefully place the cooler over the lidded CPU, connect the fan, make a few light turns for every screw and then try to boot.
You can boot to OSX to check the CPU and then shut down. Fans will kick in full speed without CPU B, but that's ok. If it doesn't boot, CPU might be bad, or most probably you need one or two additional turns on cooler screws.
Testing took a lot of time of careful connectiion and disconnection of the cooler. If you do not rush, it will be ok. Fan connector is tricky to keep in place, once it's disconnected from the assembly, but it allows to install lidded CPU without cutting the wire, and then you can install the connector back the way it was.
3. After testing we started delidding. Actually, turns out the most problematic part of the process is not heating the CPU (more on that later), but careful cutting of the resin around the lid. It super tight, razor must be very thin, and you need to be careful not to cut any resistors, which are very close to the resin. If you don't cut all of it, heating will not separate the lid from the CPU, you will think you need to more heat and you might overheat it. Cheap test CPUs were very helpful to get the hang of it.
4. After you cut the resin, you need to heat the CPU enough to desolder the lid. The very first try was with the lighter-torch. I've placed the CPU over the cup, holding with some razors stuck between the lid and the CPU. The problem was that after it got delidded, everything feel into the cup, and the lid quckly stuck back to the CPU. I've then had to reheat again, and the CPU was dead (tested).
5. After that I've tried using hot iron method, and it worked magically. Spread some cooling paste over the lid, turn the hot iron on. Once it's hot enough, press into the CPU, it will glue to it because of the paste. Then hold over a cup or glass. As solder melts enough, it will pop, CPU will fall into the cup, and the lid will remain glued to the hot iron.
You can see this method here:
Seriously, this is the easiest way, I've delidded 7 CPUs one by one using it, all survived.
6. After CPU is cool enough, take the razor and remove solder from the die. Don't worry, you can damage the die with the razor, only solder will be removed. Just be careful not to cut any resistors.
7. After that I've also used some very fine sandpaper (3000, 5000 and then 7000 grit), but that's optional.
All CPUs are now functioning perfectly, even though I've accidentally cut half on resistors on one of them.