Vibration doesn't work when the phone is completely assembled.

Hi everybody. I recently changed the LCD screen of my iPhone 5s (third party, works perfectly). When I reassembled the phone, I realized that the vibration was not working. I opened the device again, and realized that the vibration works perfectly as long as the LCD is not completely inserted. As soon as I press the LCD to make it fit into the back case, the vibration stops working. I think it is some kind of contact's fault. Any suggestions? Thanks in advance.