Backlight Flickers after iPhone Screen Replacement
I have come across this problem several times and I have found the reason why. It usually happens when you disconnect the screen or the battery without shutting the phone down properly.
Once the screen flickers, just turn the brightness down until the flickering stops. After some time passes, slowly increase brightness so that the flickering is not noticeable, after some time you can increase the brightness to full and the screen will be fine.
I tested this out on several screens and it does occur when disconnecting the lcd or battery while powered on.