One attribute of membrane switches that stands above the rest is the ability to operate in wet environments. The membrane switch front face or overlay is one unbroken sheet of water resistant plastic and provides an effect barrier against liquid ingress. The Achilles heel for membrane switch sealing is generally the connector ribbon cable area. The ribbon typically comes out the back of the switch and because the ribbon is made of the same material as the circuit, a filler piece replaces the ribbon cable shape in the materials of the membrane switch. The gaps on either side of this ribbon cable filler is where liquid can enter the switch.
Typical membrane switch design
A gasket design can solve this problem. A gasket design membrane switch does not have a tail filler therefore there is no direct pathway for liquid ingress.
The gasket layer is usually the same thickness as all the circuit materials combined. The cost of a gasket design can be higher because of the extra materials required to make the gasket. A gasket design works well when you have enough room but be careful if the area around the keys and tail exit is minimal. The surface the gasket switch is applied to is also critical to the success of the design. The surface must be smooth and free of contaminates and oils. The gasket adhesive must also be compatible with the mounting surface materials.
Another option for sealing is an RTV design. This is preferred over the gasket design in many situations because it does not require the gasket, however, the cost is a little more than a standard switch. In this design the RTV is inserted into the gaps surrounding the tail filler. The RTV sealing process is preferred when the area around the keys and tail exit is minimal.
Do you have application that comes into contact with water? How do you deal with that? Does it work?