The buttons and contacts are adhered to a thin rigid greenish fiberglass backing. Slice between this and the aluminum housing.

It is very difficult to remove the button flex cable without damage. If you need the cable intact consider adding heat with the iOpener to help soften the adhesive further. Be patient and keep applying adhesive remover every minute or so for several minutes before attempting to remove the cable.

Use spudger or blade to slice behind the button board.

There is solid aluminium directly under the buttons. Slicing straight down should not damage any other components.