One of the FBI’s Major Claims in the iPhone Case Is Fraudulent 10 years ago
This. The chip needs to be desoldered, cleaned (remove a layer of epoxy resin) and then finally reballed (secure a 0.3mm ball of solder on each of the > 64 connectors) just to get the on the chip reader.
Once you've done that you need to reverse the process.
I've done a few of these and they still scare me. Its not a trivial process.