IS the Daughter board optional to retain touch ID?

"Hi Viet, I have been waiting to answer this question because I wanted to see if anyone with lot’s of experience on these devices would answer. I have not opened up one of these bad boys yet but IMHO, the daughter board is not involved in the Touch ID functions at all. All Apple devices have the “uniqueness” of the TouchID embedded into the actual Home Button/Flex, not any daughter boards or even the main logic board.

Additionally, several suppliers sell the replacement screen with and without a daughter board which means they can be interchanged. They do require some soldering so you’ll need to decide if you want to transfer the original or buy a screen with one already installed."

Hi I had actually emailed ifixit in order to find out if the 399 cost more because the daughter board was already soldered. But the response I got was I’m not sure if it soldered. My guess is that when looking at he description of lcd and digitizer it mentions that you would have to micro solder. But once you get to the more expensive one there’s nothing about micro-soldering

"That little daughterboard I'm guessing it's for the smart cover sensor? That one is needed so that the iPad doesn't auto-lock itself if you wrap fold the smart cover to the back of the iPad.

It’s like what the iPad Air 1, 2, 4,5 and 6 use."

I have replaced the screen multiple times on the iPad Pro 12.9 2nd Gen with a daughter board pre-installed and can confirm Touch ID is not affected. If you do have issues with Touch ID after the replacement, that part quality may not be 100%.