Bootloop After SIM Repair iPhone 7

Hi dear community,

i have a Problem with an ipHone 7 here. The iphone 7 didn't recognized the SIM, so I reballed LBPA_RF and wanted to test, if iPhone recognises the SIM again. The Apple Logo appeared, and then it shuts down and want to reboot again. No matter if charging cable is plugged in or not. The same is when I unplug the battery and connect only the Charger in. So I thought there is something faulty with the U2 IC or the Gas Gauge aka Tigris Charger. I reflowed them two but nothing happened and now the Display is flickering. Do you have any Ideas? i have a dozen of iphone 7 here which have the same Bootloop problems. Any help would be appreciated. Thanks a lot :)