The motherboard is held tightly to the black plastic midframe by plastic clips, and rumble motor wires are soldered to the motherboard on both sides.

The blue circle is the plastic midframe piece holding the motherboard in place.

The yellow piece is a routing clip for the rumble motor wires.

The motors need to be moved to cleanly access the back of the motherboard, either by desoldering the motor wires, or softening the adhesive on the motors with isoprophyl alcohol.

Once the motor wires are removed, pry back the plastic pieces of the midframe on each end of the controller and pull up on the motherboard to remove it.