How to Fix iPhone 7 Plus Boot into Recovery Mode
We have received an iPhone 7 Plus motherboard from our customer, when boot it up, the iPhone enters recovery mode automatically, once restore the system, the iTunes reports error code. In this article, we will reveal how to Troubleshoot iPhone 7 Plus boot into recovery mode and fix it with NAND replacement. Hope you enjoy our sharing.
Step 1 Function Test
Assemble the motherboard, connect to the DC Power Supply and boot up the iPhone, the iPhone 7 Plus screen stuck in recovery mode with plug to iTunes icon.

Step 2 Diagnosis
Connect the iPhone 7 Plus to PC and restore the system, an unknown error 9 is discovered (iPhone error 9 is mostly caused by failed NAND), next we will troubleshoot the NAND.

Step 3 Troubleshoot and Repair
Unbuckle the screen assembly and take off the motherboard, then heat up the motherboard with the hot air gun and use the glue-removal knife to clean off the sticker around the NAND. Keep on heating the NAND evenly, until it can be separated from the motherboard with a scrape knife.

Desolder the solder pads with soldering iron, solder flux and solder wick, then scrape off the rest sticker and clean with PCB cleaner.

Solder the new NAND with the hot air gun (pre write the old NAND data in the new NAND).

Step 4 Reassemble & Test
Reassemble the motherboard after cooling down, then connect to the PC to restore the system. Boot up the iPhone again after system restoration, the iPhone enters activation interface normally, repair completed.

Please refer to below detailed video:
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Tools and Materials Used in This Video:
Solder flux
Hot air gun
Microscope
Tweezers
Soft brush
PCB cleaner
Cleanroom wipes
Desoldering braid/solder wick
Rework station
Glue-removal knife
Scrape knife
Spudger
New NAND
Thanks for sharing. Actually, apart from the fact that a hardware failure with the iPhone can cause this problem, in most cases, it is the iPhone software issue that leads to the situation. Under such circumstances, using a technical repair tool like Joyoshare UltFix is the best solution. Generally, such a tool will not cause any data loss in the process. Of course, if it is the hardware issue that results in this trouble, go to the Apple store to repair it. It is not suggested that you repair yourself if you are not a technician.
https://www.joyoshare.com/ultfix-for-win/