One of the most complex repairs on an iPhone is a screen replacement repair, before you attempt this repair be sure to have sufficient time to complete the task, and have a clear working space for your iPhone and the replacement screen to sit in while working on them.
For a replacement screen repair it is necessary to completely disassemble the iPhone, therefore I would suggest that prior to commencing the repair get a few small pieces of paper in order to label your parts, and I particular the origin of the screws. Label them as follows; Metal Back Screws, aluminum back case, and motherboard lay them out on the workspace in this order with a small space between them for the other iPhone components and replacement screen to lie in.
The tools and equipment required for this repair are; a case opener, a small Phillips screwdriver, a paperclip to eject the SIM tray and the iPhone replacement screen, once you have these to hand and the paper labels lined up. Be sure to have clean hands before starting the repair.
Firstly remove the SIM tray do this by inserting the paper clip in the hole on the topside of the iPhone next to the power button, when the clip is inserted, the SIM tray should eject. Next, use the case opener to remove the plastic back of the iPhone. Lay these two components next to the paper labels, after you have fitted the replacement screen into your iPhone you will need to reverse the order of these instructions to reassemble the iPhone. For this reason, I would suggest placing them furthest from you next to the aluminum paper label.
The next step is to remove the two small screws on either side of the back securing the metal casing, and another screw located top, middle of where you removed the plastic back placing these on the paper label. Once you have completed this, take the case opener again and carefully run it along both sides of the iPhone to loosen the back away from the frame you will notice the metal back is secured by a wire ribbon, carefully detach this from the main section of the Iphone, not the metal back end.
The next step in the screen replacement repair needs caution it is required to remove the iPhone antenna cable, secured by glue in three positions, carefully pry it loose of the glue spots. After this, you will need to remove 10 screws from around the sides of the iPhone, and place them on the paper label Outside Case after this remove the 3 screws securing the motherboard. You need to remove the motherboard at the same time as the battery as they are soldered together, once you have done this you can carefully detach the remaining iPhone frame.
The next step is to remove the LCD screen in order to fit the replacement screen this is possibly the most difficult part of the repair and needs to be done with extreme caution. Loosen the 3 clips on the sides of the screen and slowly begin removing the LCD, you will see some wires are intertwined into the Iphone carefully guide them through the frame and, they will slide right through.
Once you have completed this, take the iPhone screen replacement and insert it into the phone, carefully trace your steps to ensure that no errors are made when assembling the iPhone back to its original state.