I show the process for a CPU swap in this video. This procedure is usually only necessary for cases of extreme physical damage like when the iPhone is run over by a car and your motherboard has snapped. However, it is also sometimes necessary when a technician that has little experience attempts to do work that he is not ready for.
In this case, the last shop had managed to get the phone to boot but they pulled apart the layers of the motherboard with no clue as to how to get them back together. In the process of attempting, they severely overheated the motherboard. I found shorts on the main power rail, a NAND power rail, and an EEPROM power rail. There were also surely others that went undiscovered as I found it futile to keep attempting to diagnose the dead board. There were bumped and missing components and the board was drowned in flux. There was also tons of loose solder balls from overheating.
It was clear this was the last tech's first attempt at this type of procedure. The customer had told the tech how important data was but he should have had greater suspicions when the tech told him he needed to order tools to complete the job. This job still ended up being recoverable, but CPU swaps cost the customer more and would have been completely unnecessary had it come to me first.
This video only briefly touches on the damage and is mostly a demonstration of how to address this type of damage; that being a CPU, NAND, and EEPROM transplant.
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