Structures for membrane switch we usually adopt:

Structure for non tactile membrane switch

No tactile feeling when pressing.
More than 5 million times’ actuation life.
Can be embedded LEDs, inserted EL or EMI/ESD/RFI Shielding layer.

Structure for metal dome membrane switch

Metal Dome in switch
Offer good click feeling when pressing
More than 1 million actuation

Structure for poly dome membrane switch

Poly dome in switch.
Has similar click feeling and longer actuation life comparing metal dome.
Cost effective competing metal dome.

There are other options for membrane switch, such as embedded LED, inserted EL back light layer, inserted ESD or EMI/RFI shielding layer and sealed structure (water proof function）:

Embedded LED

Gluing single or bi-color LEDs on silver circuitry.

LEDs come in a variety of colors such red, yellow, green.

The LED window area is generally clear or semi-transparent.

The LED window is usually embossed to hold the LED inside.

Inserted Electroluminescent (EL) layer

Inserted between the graphic overlay and circuitry layer,

Can light when it is powered at dark night, so we can press the keys easily.

Can be powered by EL driver supplied by us.

Inserted shielding layer

Can be made of printed silver net or foil, carbonate net or aluminum foil.

Can avoid damage from ESD or EMI/RFI.

Has to be connected to the ground.

For membrane switch with Shielding layer, all silver lines on the circuitry layer have to be more than 3 mm away from the edge of the membrane switch, which is another measure to avoid ESD damage.

Sealed structure with water proof function

Applied in outdoor use or moist condition

an extra waterproof gasket can be placed around the circuit layer.

Width for the gasket should be more than 5 mm.

Water proof can reach IP 67.

If tail is toward membrane’s center and within membrane frame, no extra gasket is requested.