This is the method used by professionals to reflow BGA chips. It's the only way to ensure that you get the chip to the proper temperature to liquefy the solder without also damaging nearby components.
Here's the disassembly video I referenced: [ Ссылка ]
And the following is a summary of the steps I took:
1) Disassemble the phone as shown in the above video, and also take off the heat shields from the motherboard
2) Apply flux under the main BGA chip
3) Put the motherboard on an underheater, such as a griddle, and use standoffs to keep the board about 1 inch above the underheater surface
4) Apply Kapton tape all around the BGA chip to prevent excessive heating of nearby components
5) Place thermocouples around the chip, wedging them in where the chip meets the board. Hold them in place with Kapton tape
6) Turn on the underheater and slowly increase its temperature to 200 degrees Celsius. Go up 50 degrees at a time and wait 10 minutes in-between each temperature increase.
7) Position the reflow machine nozzle about 3/4 of a centimeter above the chip
8) Turn on the reflow station. Set it to 25% airflow and 100 degrees Celsius.
9) Increase the reflow station temperature by 4 degrees Celsius every second, until the thermometer attached to the thermocouple measures 230 degrees Celsius. Once it reaches 230, hold it there for 10 seconds.
10) Decrease the temperature by 4 degrees every second until the reflow station is back to 100 degrees and then turn it off.
11) Slowly decrease the underheater temperature in 50-degree increments until it's off.
12) Reassemble and enjoy.
