For data recovery I need to desolder a BGA 153 eMMC chip from a dead phone. I'd like to maximize my chances of NOT destroying the eMMC chip in the process (the other remains of the phone do not matter since these are dead already). I've already watched various instruction videos and I'd say I have an idea of the general process.
I do have a cheap Chinese hot air station where the temperature can be set between 100-500 degrees Celsius (but I don't know how accurately that actually works) and where air speed can also be selected.
For target practice I just unsoldered some DDR3 chips from some old PC's memory PCB (these chips where not glued on - it was just the solder that held them in place). I used a nozzle about the same size as the chip and put flux all around the chip before heating. I always used a low air speed (2 on a scale to 8). I progressively increased temperature and each time heated for 2 minutes to test at which minimum temperature the chip would come loose. For the DDR3 chip it actually took me 385 degrees celsius (but maybe the displayed temperature is just wrong)!
With regards to the eMMC chip I had so far found information that 240 degrees should be sufficent to unsolder it (supposedly its solder melts at 225 degrees).
Is it to be expected that an eMMC chip would come off at a so much lower (240 instead of 385) temperature than a DDR3 chip? Or is this just an indication that the temperature reading on my hot air station is way off?
Should I rather be using some higher air speed for this kind of job?
Would it make sense put some thermal isolation on the backside of the phone's PCB to reduce heat emission?
What type of low melting point solder should I use if I wanted to directly solder some wires to the eMMC chip? Or what would be the right type for reballing (leaded, lead-free, etc) if I was so put it onto some kind of breakout board?