iFixit

Rear of motherboard showing some signs of corrosion to battery contacts.

Depending on the nature of the liquid damage, removing this shield may not be necessary, and doing so risks damaging the small components mounted on the logic board. If you decide to remove the shield, proceed cautiously and use a plastic tool such as a spudger, or a plastic opening tool to lever off the shield.

Look for the dimpled tabs on the shield that reach down over the tabs attached to the mother board.

Using your plastic tool, catch the edge of a dimpled tab near a corner of the shield, and pry it up away from the logic board.

Being careful of all the tiny surface mounted components, work your way around the available edges until the shield comes free.

Submerge the logic board in isopropyl alcohol, and allow it to soak long enough to loosen hardened residue, and to displace any remaining water or other liquid. Use a soft brush to remove visible corrosion and residue.

Residue from motherboard left in isopropyl alcohol container.

Clean all flex ends, battery contacts, connectors, chips, and fuses on motherboard with a soft brush.

Repeat cleaning if necessary, or if traces of residue are still visible.

Allow the logic board or other parts to dry completely before reassembly.

Wipe LCD with cloth moistened with isopropyl alcohol. Immersion isn't advised, as liquid may leave a mark behind the LCD.

This is the screen after cleaning. Water mark is no longer visible.