Push a plastic opening tool (or, if you don't have one, use your fingernail) into the small opening on the left side of the back camera (near the power button) to pry open the back cover.
Take the corner of the back case closest to the small opening between your fingers and separate the back case from the phone.
Press the microSD card (if you have one) deeper into its slot with the flat end of a spudger (or your fingernail) until you hear a click.
After the click, remove the spudger to release the card. The card will pop out of its slot and you will be able to extract it.
For reassembly, you'll need to press the card back into its slot until you hear a click.
Use a plastic opening tool to lift the battery from the case. You need to insert the tool into the indentation above the battery compartment to do this.
There are eleven Phillips screws (4.0 mm) securing the midframe to the display assembly. Remove them.
Wedge in the plastic opening tool between the midframe and the front panel assembly (the side of the phone).
Move the opening tool down the line.
In order to separate the corner of the midframe from the display assembly, push the plastic opening tool down.
Continue sliding the plastic opening tool until you've freed the last of the clips on the power button side of the phone.
Disconnect the vibrator/power button assembly cable connector with a spudger.
You need to disconnect the antenna and display cable connector as well.
Disconnect the front-facing camera connector.
Disconnect the headphone jack cable connector.
Disconnect the digitizer cable connector.
Disconnect the antenna cable connector from the motherboard with a spudger.
Disconnect the soft button and the USB board cable connector as well.
Remove the motherboard.
In order to prevent ESD damage you need to hold the motherboard by its edges. Make sure that it doesn't touch any cables while you're separating it from the display assembly.