Hello, sorry for my poor english, but i will try to explain how i fix this problem in a IPHONE 5S. The problem in my phone start wen it fall to the ground, then the touch screen start to go crazy. I try a lot of things to solve this problem because it was imposible to use the phone. First i change the battery, the problem still remain, then i replace the screen, but the problem still there. So i realise that the problem was in the board.
The board have some metalic contacts to make discharge or something like that from static or whatever, when you put a screen those contacts must touch the metalic back of the screen, if those contacts are not touching the metal or are dirty this make the touch go crazy, so i clean those contacts and separated enough to make sure ther will be a good contact then, voila!!!! The screen was perfect again.