Polydome Silver Flex Membrane Switches: What are They, What do They do?

A Definition of Polydome SilveAr Flex Membrane Switches
A polyester dome silver flex membrane switch is a tactile membrane switch that features a polyester overlay and silver conductive ink. Membrane switches are momentary switching devices in which at least one contact is on, or made of, a flexible substrate. The switch is tactile because it snaps or clicks when the user presses it, thanks to the dome that lies underneath the switch. The tactile response lets users know that the button has been pressed properly. Various dome shapes and sizes are available, and the different sizes result in different actuation forces for user feedback.

Polyester Dome Facts  
Polyester is an overlay of choice because it is more durable than switches with overlays made from other types of materials, such as polycarbonate. Polyester especially is a good choice if your application has more than 50,000 actuations; in fact, life cycle tests show that polyester may be actuated more than 1,000,000 times in a tactile switch without showing signs of wear. If you are looking for appropriate levels of tactile feedback in your membrane switch, make sure your overlay thickness is between .006 and .010.
In the case of polyester dome (also known as “polydomes”) silver flex membrane switches, the tactile response is achieved through the use of polyester domes that are formed either in the circuit or in the graphic overlay layers. Changing the diameter and height of the polydome when constructing the polyester dome silver flex membrane switch will affect the dome’s actuation forces. It’s important to note that polyester dome membrane switches are much quieter than their metal dome counterparts, so they are often used in sensitive environments including hospitals and recording studios.
Polydomes often are formed into the top circuit of membrane switches. As polydomes require expensive machined tools that typically are built specifically for each design, they become more cost effective as volumes increase because they do not require individual assembly. Generally, polyester domes are an economical choice if the order exceeds 1500 domes.
Information About Silver Conductive Inks
The “silver flex” in the polyester dome silver flex membrane switch comes from screen printed conductive silver ink circuits. Silver inks are specially prepared suspensions of finely milled silver particles in a variety of resin systems that are widely used to produce conductive patterns on flexible substrates in the construction of membrane switches. The circuit closes when the user presses the switch because of the conductive silver ink that is used in creating the circuit.
Benefits of Polyester Dome Silver Membrane Switches
Polyester dome silver flex membrane switches are a popular choice because they deliver high-density membrane keypads at a lower cost than traditional metal dome membrane switches. Polyester dome membrane switches also are 3D tactile buttons that are formed during a single stage thermal cycle.That’s why polyester dome silver membrane switches are used in several applications: information-dense input/output devices, noise-sensitive environments, tightly-controlled actuation experiences, industrial, and consumer electronics.
There are several benefits associated with using polyester dome silver membrane switches, including:

• Tightly specified actuation forces due to highly accurate tooling
• Softer actuations that are extremely quiet
• Higher keypad densities are possible than with metal dome membrane switches
• A lower cost method for producing high-density input/output devices

Lighted Polydome Silver Flex Membrane Switches 
Polyester dome silver flex membrane switches may incorporate lighting or backlighting in their design. It is fairly common to find embedded light emitting diodes (LEDs) or fiber optic backlighting or electroluminescent (EL) backlighting in polyester dome silver membrane switches.

• Embedded LEDs – Small, surface-mounted LEDs are often included in membrane switches. Often, silver conductive epoxies are used to mount the LEDs to the circuit.
• Fiber Optic Backlighting – One advantage of fiber optic backlighting is that it offers uniform light over a large area. This backlighting is low in power consumption and sometimes requires only one LED.
• Electroluminescent Backlighting – While EL backlighting also provides uniform light over a large area, it does not have the lifespan of LEDs.