What is a Membrane Switch?
A membrane switch is a type of control panel printed on a thin piece of polyester or polycarbonate. The switch uses metallic or electrically conductive ink. These switches are used for home appliances and manufacturing or construction industry products. They are simply a way of creating a user interface with an electronic device, like a touch screen or computer keyboard. They are used in designs that have size constraints, such as television remote controls. They are also used in devices that must be easily cleaned, such as portable, folding computer keyboards.
Devices that Use Membrane Switches
The control panel of a microwave oven is a membrane switch. It typically has a tactile feedback printed on the graphical interface. Many other home appliances, including ovens, washers and dryers, or even security systems use these interfaces. In these examples, the membrane switches are simply an alternative to a conventional number pad or keyboard. Even so, they can have any type of electronic circuit printed on them and any type of graphical design. The technology is simply a means of interacting with an electronic device. It can be used to control any device that runs on electricity.
For example, it can be used as the interface for a musical instrument, such as a synthesizer, for a light switch or for an electric blanket. There are simple switches that control a single function, such as the power switch of a lamp. There are also more complex designs such as a computer keyboard. They may have a rubber keypad on the top layer, like on a remote control. They also may have a flat and smooth or tactile design, like on a microwave.
Tactile switches require greater force for actuation and therefore must be made from thicker material. These switches have small domes embedded over each button on the keyboard to raise it up slightly so that users can feel the key layout. Non-tactile switches are completely flat. Because they require very little actuation force, they can be made from material as thin as 0.02 inches. Examples of non-tactile switches include dimmer switches for overhead lights, or tracking pads on laptop computers. They respond to a very slight actuation force and typically hold up for one million one million or more actuations, depending on the construction material.
Material Quality Affects the Number of Actuations
It is not only the type of material, but also the material quality, which affects the number of possible actuations over the lifetime of a membrane switch. Industrial uses can require a more than 50,000 actuations. In such an industry, replacement costs are a factor. Polyester switches can lower costs for such industrial use by providing well over one million one million actuations. Typically, polyester shows no signs of wear at this point, although because it is a more durable material than polycarbonate, it requires extensive hydroforming, retooling and reblading when die-cutting the pieces. Therefore, it may be more cost-effective to use aluminum or polycarbonate if fewer than one million actuations are needed.
The substrate is not a limiting factor in the lifetime of the switch. The other materials typically wear out before the circuit-printed layer does. The LED backlights and LCD panels will most likely need to be replaced before the polycarbonate substrate wears out. Using low-quality parts increases the number of repairs needed and the interruptions to the production schedule. They also result in customer returns, warranty repairs and lost revenue.
LED backlighting is not always ideal because it produces uneven illumination across a large area. To light up a keypad with an appealing and evenly distributed glow, fiber optic fabric or electroluminescent (EL) material works best. EL lamps are less expensive than fiber optics. They offer a wide variety of colors, although the quality of the phosphor used in the lamp greatly affects the lifetime of the backlight. Additionally, EL lighting becomes dim when it reaches its half-life. Thus it is a bad choice in applications that require consistent illumination. It can be used to light a keypad for use in the dark; However, if the keypad is always in a dark location, fiber optic backlighting is appropriate.
Industries that Use Membrane Switches
Every industry in the economy uses this technology in virtually every application. It can be used as an interface in any low-voltage electronic device. Such devices include embedded computers, machinery controls, vehicle user interfaces, security systems and wearable electronics. Consumer goods contain a wide variety of examples of membrane switches. Any company that relies on microprocessor-based devices or electronic machines to manufacture products or deliver services probably has dozens or hundreds of these flexible electronic circuit boards in use throughout the production floor.
Construction businesses use membrane switches to control the embedded computers in heavy machinery. Laboratories use them to control the temperature in refrigerators and incubators, Banks use them to control the electronic locks on safes. Employers in all industries use them on employee time card machines. In the area of consumer goods, they are used as telephone number pads, keyless entry devices and circuit boards on electronic toys.
Depending on the application, they can be used with four to nine layers and be made from a variety of materials. The layers contain the graphical user interface, the circuit board itself, the backlight, the buttons as well as the material on which these layers are mounted. For flexible keyboards and number pads, such as folding computer keyboards, polycarbonate material is combined with soft rubber. Keyboards typically have tactile interfaces. for those that do not, they can simply use buttons printed on the graphical interface. The circuit board and interface are cut using a computer-controlled die cutter, and the interface can be designed with any graphical layout.
Putting It All Together
Designing an effective membrane switch takes experience and planning. When a large number of switches are required, such as in the manufacturing process, the number of actuations must be taken into account. Usually, consumer devices do not require one million or more actuations, and polyester substrate is expensive to produce. The other materials included in the switch, such as the backlight and LCD panel, should match the quality of the user interface and printed substrate.