A membrane switch is an interface between user and machine, enabling an operator to communicate with equipment, instrumentation, or machinery. A membrane switch is a printed electronic circuit that uses pressure to open and close a circuit. The membrane switch circuitry is most often screen printed using conductive inks which are typically made of silver or carbon. Membrane switches are part of a range of devices considered to be user interfaces or human machine interfaces (HMIs) along with touch screens and mechanical switches.
A typical membrane switch assembly typically consists of six to seven main layers:
Silicone Elastomeric Rubber Keypads
Silicone rubber keypads use compression-molded silicone rubber with conductive carbon pills or with non-conductive rubber actuators. They have exceptional resistance to extreme temperatures and aging, making them an ideal choice if reliability is a prominent concern due to likely environmental influences.
A rubber membrane switch uses compression-molded silicone rubber with conductive carbon pills or with non-conductive rubber actuators. Rubber keypads are relatively inexpensive on a per-piece basis, but require fairly expensive tooling, usually making them a design choice for higher-volume projects.
Silicone rubber keypad switches have numerous features that set this type apart from other traditional membrane switch designs. Some of the main differentiating features of this type make the silicone rubber keypad switch an ideal choice for applications requiring more durability or better resistance to exposure to moisture, chemicals, or other compounds.
Some of the primary distinctive features of silicone rubber keypad switches include:
Silver Flexible Membrane Switches
Silver Flex membrane switch panels utilize screen-printed silver and carbon conductive inks printed on flexible polyester layers separated by an adhesive spacer. This is the most common design used in flexible, custom membrane keypads, offering a slim, space-saving design.
Silver Flexible circuity is also more cost-effective when compared to electromechanical switch assemblies and the process of screen-printing conductive silver inks onto a flexible, film substrate poses less potential threat to the environment compared to chemically etched copper.
Silver Flex membrane switches offer you a variety of design options:
Additionally, a Silver Flex membrane switch uses a graphic overlay, which also has a number of design options:
The Copper Flex Membrane Switch constructions are ideal for smaller designs, where space is at a premium, or where dense circuit patterns or trace routing limitations exist. Copper Flex membrane keypads utilize silver or copper layers which are laminated to a dielectric layer and etched away.
This switching technology combines the ability to accommodate the complex circuit patterns of a FR4 rigid printed circuit board with the flexibility of a membrane switch. Copper Flex keypads also have the advantage of being able to “hard” solder both active and passive components into the assembly, making it a good choice in high-vibration environments.
Copper Flex membrane switch panels can be produced using polyester or polyimide (Kapton) as the base material depending on your interface requirements. A very thin sheet of copper is laminated to the flexible film substrate then chemically etched away, leaving copper traces.
Copper Flex membrane switches offer you a variety of design options:
PCB Based Membrane Switches
The PCB Membrane Switch construction utilizes a printed circuit board (PCB) which can serve a dual purpose in your membrane switch design. PCB Switches are typically more costly than Silver Flex membrane keypads, but can accommodate dense circuit patterns and more complex circuit patterns compared to Silver Flex membrane keypads.
A PCB membrane switch also allows the electronic components to be “hard-soldered” into the PCB, whereas membrane switch components are placed using a polymer thick film conductive paste. With a PCB membrane switch, the PCB can serve as a rigid backer, and is also a very durable and reliable method to incorporate LED’s, resistors, LCD’s and other components.
PCB membrane keyboards offer you a variety of design options:
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