TouchID not working after touch IC repair

When doing a Touch IC repair, it can happen that too much heat is applied and that causes components on the opposite side of the board, in this case the screen assembly connectors. Surrounding the screen connectors are rows of passive components, capacitors, resistors, filters etc. and they are encased in an epoxy to protect them. When they overheat, the solder melts and the epoxy actually pulls them up off the board. This can cause all kinds of issues and the problem is that you can’t see that this happened.

Normally, when doing a repair such as this, the tech should test all of the phones functions (cameras, sensors, etc.) before giving the phone back to the customer. This way, he would have noticed the issues and could have resolved them beforehand. The tech will have to check all the functions, diagnose those that aren’t working and check all o f the related passive components near the connectors to see which ones are causing the issue.