I have assembled an iPhone 6 and it seems that everything goes fine except the NFC. The phone does not respond to the POS when using Apple Pay. I think there should be some poor connection between the logic board and NFC antenna. If so, which screws should I scrutinise to fix this problem? Thank you.

I have assembled an iPhone 6 and it seems that everything goes fine except the NFC. The phone does not respond to the POS when using Apple Pay. I think there should be some poor connection between the logic board and NFC antenna. If so, which screws should I scrutinise to fix this problem? Thank you.