Continue swinging open the back panel until you can rest it on the left edge the phone, being careful not to put any stress on the attached ribbon cable.
During reassembly, this is a good point to power on your phone and test all functions before sealing it up. Be sure to power your phone back down completely before you continue working.
Whenever you use the spudger near the battery, be very careful not to puncture the battery.
Using the pointed end of a spudger, pry the battery connector straight up from the motherboard to disconnect the battery.
To re-attach press connectors like this one, carefully align and press down on one side until it clicks into place, then repeat on the other side. Do not press down on the middle. If the connector is misaligned, the pins can bend, causing permanent damage.
Slowly lift out the motherboard, being careful not to snag any ribbon cable connectors.
The rear-facing camera module connectors loop around the motherboard, and the camera module is not secured to the phone, so it may lift out with the motherboard during this step.
Completely remove the motherboard.
When reinstalling the motherboard, check that no ribbon cable connectors are caught underneath.
This guide doesnt mention thatthe front camera and sensor array is married to the motherboard and replacing one without the other will cause face unlock to not function. This situation throws a "Certificate Expired" error and neither factory reset nor reflashing/sideloading firmware corrects this. Google support says repair or replace is the only remedy. I'm currently trying to prove that assertion wrong.
Hey J L, Did you ever manage to find a solution for the certificate expired issue? I recently replaced my front camera and sensor assembly hoping to fix broken face unlock sensor. Encountering the same certificate expired issue after replacement