Tiny buttons with bad contact

The number buttons on my calculator watch Casio CA-53W were getting unreliable (many presses to get it to acknowledge), so I took it apart.

I’m unfamiliar with the how the buttons work (make contact) and how the button pad connects to the circuit board. I tried cleaning the contacts (lightly sanding with 400grit) but seamed to make it worse. The key pad just presses against a little strip the is stuck to the circuit board.

Dose anyone know what type of contact is going on here so I can attempt to fix it. I don’t even know what its called or how it works.