MacBook SSD Repair

==Disclaimer==
This article is purely speculative, based on various facts and ideas gathered online and from random discussions in chat rooms. There might be, and obviously are, many elements I have partially or completely misunderstood. I use "most likely" in its literal sense, indicating that 30-50% of the points made here could be inaccurate. I would genuinely appreciate if someone corrects me, explaining how these processes truly work. This article is intended for repair technicians. SSD repair/replacement is not something that can be accomplished after a few hours of watching repair videos online. It requires advanced soldering equipment and the expertise of a professional repair technician.
==Little Theory==
Since 2016, the 4TBT model from Apple has been using embedded SSD drives soldered on the motherboard. The first generation of such SSD drives allowed for Lifeboat access to extract data from a broken logic board if you had the rather unique "Apple Customer Data Migration Tool (CDM) Apple P/N 076-00236", which is essentially a fancy PCI-E to USB adapter. The Lifeboat connector is essentially a plug that disconnects internal power supplies and PCI-E differential pairs, allowing the external interface to read the drive itself. There is a possibility (not yet proven) of hard-wiring a standard M.2 SSD drive connector to the Lifeboat plug. If you install an M.2 2240 SSD Drive into the chassis, you can expand to 2 TB of space or whatever capacity you find on the market.
Modern SSD drives consist of three components (excluding the power supply): the Controller, RAM, and NAND memory chips arranged in some sort of RAID array for performance and wear distribution. Internal firmware is stored in a service area on one of the NANDs and is somewhat similar to HDD firmware. It includes a bad block list, LBA Translator, self-monitoring logs, and so forth.
To replace such a drive, you need a full set of SSD Chips as well as a controller, so you can only source it from a working donor. I've heard a few stories of people being able to use the Gumstick5 (2TBT 2016-2017 model) drive as a source, but I can't confirm this.
Later in their development, Apple "removed" the Lifeboat feature by introducing the Intel-T2 hybrid architecture. This is not entirely true because they simply moved it to another place, which I will describe later.
There is no longer an embedded SSD drive, but rather a monolithic SIP NAND drive which integrates the controller, DDR cache, and NAND into a single package. It operates through the same PCI-E interface and essentially stems from the iPhone/iPad architecture. In fact, these are basically the same chips; you could even use a MacBook as a donor for an iPad or iPhone.
Apple uses different brands, including Toshiba and Sandisk, on different boards, but the principle remains the same. Each NAND functions as a separate device on the T2 BridgeOS level, and it is, indeed, mounted into a hardware RAID0-like volume, seen as a single internal drive to the end user.
It's most likely that the T2 OS (BridgeOS) itself is stored on the volume level, just in a hidden area, which makes it impossible to restore the T2 partition if you swap NAND positions or replace them, thus disrupting the RAID array. Most likely, NANDs are preprogrammed using a pogo-pin connector after board assembly. Each board has a set of pins, allowing direct, low-level access to each NAND.
==Tools==
Replacing the T2 MacBook NAND is similar to the process for the iPhone or iPad. You'll need the standard tools for underfilled chips, a stencil, and quality soldering equipment.
The most crucial tool is the JC P13 NAND configuration tool, which is currently the only one available(P11 can be used if you have dumps + probably any other P13 clone could do same job if you have dumps, however it is not really clear). This tool is used to configure the NAND before soldering them onto the board. It can also serve as a reference for purchasing replacement chips (to prepare the NAND, you'll need to specify which IC and device you have). Use MacBook NAND List as a reference. 
More info here: https://www.youtube.com/watch?v=yR7m4aUxHcM
To figure proper NAND set refer to the MacBook NAND List page. Do not forget to check your T2 memory size. 
==More Theory and Practice==
As mentioned earlier, the T2 acts as a RAID controller, which expects to see a configured set of SSDs in the correct order. This is precisely why you need the JC P13. It writes a sysconfig block (on iPhones/iPads, this is used to configure WIFI, SN, etc.) to the raw drive using a repository of original configuration images. You must select the number of chips, their vendor and capacity, as well as the target device, to ensure everything works as it should. After you've prepared the NANDs, you need to solder them onto the board in the correct order and perform a full DFU restore (since there will be no BridgeOS on the NAND yet, it's similar to the process you'd follow for an iPhone after a NAND upgrade).
After this, you should have a functional Mac once again.
Unconfirmed Possibilities:
*Partial NAND Replacement: If you had a highly shorted 2.5v rail, there's a good chance that only one NAND was damaged. You might be able to read its config block using the JC P13 and a freezer (the freezer provides higher current, and it's been confirmed to be useful in iPhone repairs to recover the original MAC/SN/WLAN config) and prepare just one NAND, meaning you won't have to remove them all.
*Whole RAW NAND Backup: Currently, devices like the Magico and JC P13 only work with small sysconfig blocks. However, it's clear that technically RAW NAND access should and could be free to use. This could potentially allow for data transfer from a faulty, shorted NAND to a good one (if it permits itself to be read under a freezer/being reset every few seconds, etc.).
MacBook M1 and Beyond:
Here's some good news. You might have figured out that T2 SSD repair/upgrade is in fact easier and more convenient than doing so on T1 MacBooks. And the process is even simpler on the M1, since M1 DFU does not require you to prepare the NANDs. You just solder them onto the board like any other chip and it works. No BridgeOS means no NAND preparation. Again use MacBook NAND List as a reference(M1 models compatible IC IDs added recently). 
UPDATE: It is not clear since which AC2 update this happened but for now DFU Restore only works only if you solder unprogrammed clean / unused NANDS. 
Yay! 
==Data Recovery Possibilities==
As previously mentioned, the Pre-T2 Lifeboat connector provides a direct interface to the SSD drive, similar to a normal M.2 NVME drive. The T2 can grant access to the internal volume using a tool called the "data transfer utility," which is only accessible to AASP providers. To run the app, you need approval and a ticket in the AASP system. It operates through a USB 2.0 interface, so the transfer rate is... well, it doesn't really matter because it can read an SSD with a dead Intel CPU/PCH part.