View A Video on Membrane Switches - A Quick Introduction
Membrane switches can be thought of as one category of interface utilities alongside touch screens, plastic keyboards, toggle switches and many other kinds of control systems. Interface utilities can be as simple as tactile switches for controlling lighting, and they can be as complicated as membrane keyboards, keyboard switches and membrane switch panels for use with computers. Custom keypad and custom membrane switch manufacturers abound; the market for membrane keypads with specialized graphic overlays is very large. Membrane switches are valued because of their low cost and versatility; they can be designed with inexpensive circuitry as well as advanced flexible circuitry for use in products that involve moving parts or that are subject to impact or vibration. Membrane switches are prized over other interface utility varieties because of their layered design. Their plastic and rubber keypads are less susceptible to accidental spills or dirt accumulation, as there are no spaces between buttons through which contaminants can pass. Some membrane keypads can even be combined with plastic and metal domes to produce a tactilely-enhanced keystroke experience.
There are three main elements to a membrane switch: the printed film electrical circuit board, the electrically insulating spacer and the top button layer, which usually features a graphic overlay. The circuit board is a thin polymer film on which a circuit pattern is printed with an electrically conductive silver-based ink. An adhesive spacer sheet is bonded to the circuit board and patterned with cutouts where electronic switches go. Tactile switches incorporate small metal domes made from nickel-plated stainless steel or other metals that are placed between the layers; when depressed sufficiently, the domes give way, which produces a sensation that confirms registry of the keystroke. A common deficiency of membrane switches is the difficulty of confirming keystrokes consistently. Tactile switches give users a confirmation of registry through the feeling of a dome being depressed, through an auditory signal or through a combination of the two. A polyester adhesive film secures these domes in place. Non-tactile switches make electrical connection through silver-based conductive ink printed on the back of the graphic overlay.
The graphic overlay, which is the visible surface of the membrane switch, can be made in many different ways. The graphic overlay is usually printed or embossed. It can involve acetate film patterned with buttons through photochemical processing, and it can be screen printed with appropriate colors and text. Depending on the device's intended application, the overlay surface can be designed to varying specifications of corrosion and abrasion resistance, heat resistance and impact resistance. Different applications call for different qualities, and because there are so many different kinds of contexts in which membrane keypads and switches are applied, there are many configurations to choose from. Once an overlay choice is made, it is layered over the circuitry and insulating layers and either attached with fasteners or with adhesives. Membrane keypads perform very important tasks. In industrial contexts, membrane keypad performance can mean the difference between properly functioning equipment and malfunctioning or even dangerous equipment. In commercial contexts, particularly in the case of building security, membrane keypad combination locks can be the last line of defense for sensitive information or areas. For these reasons, each step of the membrane keypad manufacturing process must be performed in a low-contaminant environment to ensure peak performance for as long as possible. Clean rooms are often employed for the fabrication of complex membrane keypads.
Membrane switches are a fairly new technology. They have gained so much prominence so quickly because they are easier to fabricate and require fewer materials than mechanically operated keyboards and other kinds of more complicated and resource-intensive interface equipment. Because membrane switch manufacturing requires far fewer materials than push-button keyboards and keypads, it is a highly cost-effective process. Membrane switches are also more versatile than mechanical interface utilities, and if properly constructed and maintained, they can resist contamination by moisture and particulates. This increases the length and quality of their operating lifespans, reducing maintenance costs and the cost of continuing interface utilities investments. There are some ways in which membrane switches do not measure up to the performance of other interface utilities. Personal computing, for example, requires a utility that can register keystrokes without requiring too much of an exertion from their users. Membrane keypads and keyboards often fail to register light button depressions. Tactile switches compensate for this deficiency to some extent, but not to the extent that would make them practical as permanent personal computing keyboards. That said, membrane switches can be used in far more applications than can mechanical switches and at a much lower cost.
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Membrane Switch Types
- Custom keypads and custom membrane switches are user-equipment interface utilities that are designed for use with specialized electronic devices.
- Flexible circuits are electrical signal-bearing utilities that connect control systems with processing systems; they are characterized by their flexible construction as opposed to the rigid, often brittle construction of other circuitry varieties.
- are covers that are placed over control panels to indicate the location and function of buttons.
- Keyboard switches are user-equipment interfaces that allow for the communication of commands between a user and an electronic device.
- are flat surfaces with printed symbols and outlines rather than traditional moving keys.
- are flat surfaces, rather than moving keys, that are activated with the press of a finger.
- Membrane switch panels are user-equipment interfaces that feature several control switches for the communication of commands from a user to an electronic device.
- supply the snap and complete the electrical circuit. The domes are from
pressed stainless steel or aluminum and come in various shapes, sizes
and thicknesses.
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are membrane switches made without a snap action.
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are produced by embossing domes into one of the polyester layers in
the construction, which results in a very durable tactile element with
a little more movement than metal domes. This diminishes the quantity
of layers in the assembly.
- Rubber keypads are user-equipment interface utilities that allow for the communication of commands between a user and an electronic device; they are characterized by their rubber keys as opposed to the plastic keys of other keypad varieties.
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are assembled to supply a positive snap-action reaction to pressure.
They can be attained through polyester domes made in either the graphic
or circuit overlay layer or stainless steel domes embedded in the membrane
switch.
- Touch Screens are pressure-sensitive computer display screens that act as input devices.
Membrane Switch Terms
- The degree to which a
membrane switch is able to withstand surface wear.
- This is the action of working a switch apparatus.
- The pressure necessary for collapsing the walls
of the dome on a polyester, rubber or metal keypad.
- The molecular attraction of one material to another.
The strength of the bond is determined by the surface energy in each
material.
- An adhesive applied to the back of a membrane
switch for mounting purposes.
- The minimum voltage at which the insulation
between two conductors is destroyed.
- The type of ink that consists of prepared
suspensions of carbon black and is frequently printed over silver circuitry
to diminish the potential of migration of silver. These are used for
lessening costs when the conductivity of a metal base system is not necessary.
- A material's ability to allow electrons to
flow.
- A conductor intersection insulated by dielectric material.
- A cosmetic feature of a graphic overlay in which a
button is only visible when backlit.
- An insulating or non-conducting medium.
- Used for printing
protective patterns on conductive printing to isolate selected regions
from electrical contact with other conductors. This is used for cross-overs
and tail insulation on membrane switches.
- An adhesive
layer made to hold metal domes in the keyswitch.
- A slender device that
illuminates large areas, typically used in LCD membrane switch backlighting
and control panels.
- Procedure of integrating a surface mount LED into
a membrane switch assembly.
- A way to supply a raised characteristic to accentuate
key surfaces through mechanical and thermoforming of graphical features.
This also permits an embedding of a surface mount of an LED inside the
switch.
- The extent of shininess of a substrate, commonly
identified in percentages.
- Control keypads
that use graphics for button functions for navigation on machines or process
operations. Typical graphics include arrows or symbols indicative of a
machine process or operation.
- Switch openings connected to one another to
seal the switch from moisture and other contaminants.
- A measure of the distance from the highest point of
a key to the base of the keypad.
- Embedded in membrane switch layers
to illuminate the button.
- A material's ability to resist the
absorption of water from the air or during complete submersion.
- The front layer of a membrane switch or control
panel.
- The travel that is done by the rubber keyboard or
metal dome after making contact with the circuit.
- Creating a raised surface in the graphic overlay
over the membrane keypad area of membrane switches.
- The schematic that describes the circuit output requirements
for membrane switches.
- Adhesive materials that bond after pressure
without needing heat or solvents.
- Produces a raised ridge circling the key area.
- Printing procedure that uses a stretch of mesh
over a frame, permitting the use of a stencil to discriminately allow
ink through. This is typically used for creating graphic overlays and
membrane circuits.
- Finely-milled particles of silver suspended in various
resin systems that produce conductive patterns on rigid and flexible
substrates. This is a typical conductor material for membrane switches.
- A membrane switch adhesive layer that separates circuit
layers to supply keyswitch openings, permitting the contact of conductors
when depressed.
