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Silicone rubber keypads (also known as elastomeric keypads) are used extensively in both consumer and industrial electronic products as a low cost and reliable switching solution. [1]
The technology uses the compression molding properties of silicone rubber to create angled webbing around a switch center. On depression of the switch, the webbing uniformly deforms to produce a tactile response. When pressure is removed from the switch, the webbing returns to its neutral position with positive feedback.
To make an electronic switch, a carbon or gold pill is placed on the base of the switch center which contacts onto a printed circuit board when the web has been deformed. [2] Alternately, instead of using a conductive pill, the switch itself can be made of a conductive elastomer such as rubber with a mixture of carbon.
It is possible to vary the tactile response and travel of a key by changing the webbing design and/or the shore hardness of the silicone base material. Unusual key shapes can easily be accommodated as can key travel up to three millimeters. Tactile forces can be as high as 500 g depending on key size and shape.
The snap ratio of a keypad determines the tactile feel experienced by the user. The recommended snap ratio for designers to maintain is 40%-60%; if dropped below 40% the keys will lose tactile feel but have an increased life. Loss of tactile feel means the user will not receive a ‘click’ feedback during actuation.
Snap ratio is calculated as the difference between the actuation force and the contact force of a switch divided by the actuation force. The actuation force is the force required to collapse the membrane of a rubber switch, and the contact force is the force required to maintain rubber-switch contact closure with a printed circuit board.
Mathematically, this can be represented by:
Snap ratio = (F1 - F2) / F1
where F1 is the actuation force, and F2 is the contact force.
By adding pigments to the natural silicone rubber, it is possible to create keys in various colors which can be molded together (Flowing colors) during the compression process to form a multi key keypad. Individual legends can be printed on to a key allowing full customization of the keypad for its application. Techniques have also been developed to allow for keypads to be spray painted and legends then laser etched through the paint coating. This allows individual key to be illuminated using SMT LEDs placed on the printed circuit board. Also several coating materials such as Sealplast coating can be done to ensure a smooth surface where the printed legend last longer with good feeling of touch.
Laser etching is the laser controlled process of removing the top coat layer of a painted keypad (usually black in color) to reveal lighter colored layer below (usually white). The effect is to produce an enhanced backlight effect by only lighting the legends on a keypad. By combining laser etching with either electroluminescence (EL) or LED backlighting in a range of color options it is possible to produce an interesting range of effects.
Also the contact resistance can be customized based on electronics need where contact pills can be of different resistance. A general carbon pill can be of around 20 to 100 ohms, a low resistance contact pill can be up to 10 ohms. Gold or Supra-Conductive pills can be used to obtain a resistivity as low as 1 ohm.
Because silicone is an insulator, silicone rubber keypads are naturally shock resistant. Silicone rubber keypads are also naturally vibration resistant, and they can be customized to be water and dust resistant as well. For this reason, rubber keypads are often suitable for rugged applications. Rubber keypads can also be easily backlit, as silicone rubber acts as an efficient light diffusion medium. [3]
Common applications of silicone rubber keypads include remote controls for TV, video and HIFI units, electronic toys and games, and industrial control equipment.
Industrial silicone rubber keypads such as ones produced by CTI Electronics Corporation are used in the medical, marine, or, military are typically sealed comply to specific industry standards such as NEMA or IP66 for protection against elements such as liquids or dust.
Prior to eliminating keypads in favor of touchscreens, mobile phone handset manufacturers were the main consumer of rubber keypads worldwide.[ citation needed ] Their involvement has led to advances in technology including the use of hard plastic key tops bonded to a rubber keypad and also the use of embossed Mylar layer to produce an enhanced tactile response.
With the increased use of low-current switching in automobiles, silicone-rubber keypads are being used extensively as switch mechanisms for various buttons such as window lifts and steering wheel mounted controls. Low-resistance pills such as SC pills and gold pills, along with short-stroke metal-dome contacts, are widely used in these settings.
The technology of computer keyboards includes many elements. Among the more important of these is the switch technology that they use. Computer alphanumeric keyboards typically have 80 to 110 durable switches, generally one for each key. The choice of switch technology affects key response and pre-travel. Virtual keyboards on touch screens have no physical switches and provide audio and haptic feedback instead. Some newer keyboard models use hybrids of various technologies to achieve greater cost savings or better ergonomics.
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of switch is an electromechanical device consisting of one or more sets of movable electrical contacts connected to external circuits. When a pair of contacts is touching current can pass between them, while when the contacts are separated no current can flow.
A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking utensils, thermal insulation, and electrical insulation. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, and silicone caulk.
A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound, light and heat.
A miniature snap-action switch, also trademarked and frequently known as a micro switch or microswitch, is an electric switch that is actuated by very little physical force, through the use of a tipping-point mechanism, sometimes called an "over-center" mechanism.
A chiclet keyboard or island-style keyboard is a computer keyboard with keys that form an array of small, flat rectangular or lozenge-shaped rubber or plastic keys that look like erasers or "Chiclets", a brand of chewing gum manufactured in the shape of small squares with rounded corners. It is an evolution of the membrane keyboard, using the same principle of a single rubber sheet with individual electrical switches underneath each key, but with the addition of an additional upper layer which provides superior tactile feedback through a buckling mechanism.
A membrane keyboard is a computer keyboard whose "keys" are not separate, moving parts, as with the majority of other keyboards, but rather are pressure pads that have only outlines and symbols printed on a flat, flexible surface. Very little, if any, tactile feedback is felt when using such a keyboard.
An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, forming a seal at the interface.
A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independent of the direction of current.
Sheet resistance, is a measure of resistance of thin films that are uniform in thickness. It is commonly used to characterize materials made by semiconductor doping, metal deposition, resistive paste printing, and glass coating. Examples of these processes are: doped semiconductor regions, and the resistors that are screen printed onto the substrates of thick-film hybrid microcircuits.
A membrane switch is a custom switch assembly that can open or close the conducting path in an electrical circuit and requires at least one contact made of or attached to a flexible substrate. Its assembly differs from traditional mechanical switches: a membrane switch's construction consists of various thin layers sandwiched together using pressure-sensitive adhesives. Each layer in a membrane switch assembly serves a different purpose, and custom features require the addition of specialty layers. Typical implementations arrange multiple membrane switches across its layered structure to form a keypad interface that allows human interaction to control electronic systems.
Metal rubber is a broad, informal name for several conductive plastic polymers with metal ions produced by NanoSonic Inc. in cooperation with Virginia Tech. This self-assembling nanocomposite is flexible and durable to high and low pressures, temperatures, tensions, and most chemical reactions, and retains all of its physical and chemical properties upon being returned to a ground state. NanoSonic’s Metal rubber™ is an electrically conductive and flexible elastomer. It can be mechanically strained to greater than 1000% of its original dimensions while remaining electrically conductive. As Metal rubber can carry data and electrical power and is environmentally rugged, it can be used as a flexible and stretchable electrical conductor in the aerospace/defense, electronics, and bioengineering markets.
Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations. Silicone rubbers are often one- or two-part polymers, and may contain fillers to improve properties or reduce cost.
Conformal coating is a protective coating of thin polymeric film applied to printed circuit boards (PCB). The coating is named conformal since it conforms to the contours of the PCB. Conformal coatings are typically applied at 25-250 μm to the electronic circuitry and provides protection against moisture, dust, chemicals and temperature extremities.
Converting companies are companies that specialize in modifying or combining raw materials such as polyesters, adhesives, silicone, adhesive tapes, foams, plastics, felts, rubbers, liners and metals, as well as other materials, to create new products.
Dielectric elastomers (DEs) are smart material systems that produce large strains. They belong to the group of electroactive polymers (EAP). DE actuators (DEA) transform electric energy into mechanical work. They are lightweight and have a high elastic energy density. They have been investigated since the late 1990s. Many prototype applications exist. Every year, conferences are held in the US and Europe.
A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Replacing early punched cards and paper tape technology, interaction via teleprinter-style keyboards have been the main input method for computers since the 1970s, supplemented by the computer mouse since the 1980s.
Elastomeric connectors, also known by the registered trademark ZEBRA connectors, consist of alternating conductive and insulating regions in a rubber or elastomer matrix to produce overall anisotropic conductive properties. The original version consisted of alternating conductive and insulating layers of silicone rubber, cut crosswise to expose the thin layers. They provide high-density redundant electrical paths for high reliability connections. One of the first applications was connecting thin and fragile glass liquid crystal displays (LCDs) to circuit boards in electronic devices, as little current was required.
Quantum tunnelling composites (QTCs) are composite materials of metals and non-conducting elastomeric binder, used as pressure sensors. They use quantum tunnelling: without pressure, the conductive elements are too far apart to conduct electricity; when pressure is applied, they move closer and electrons can tunnel through the insulator. The effect is far more pronounced than would be expected from classical (non-quantum) effects alone, as classical electrical resistance is linear (proportional to distance), while quantum tunnelling is exponential with decreasing distance, allowing the resistance to change by a factor of up to 1012 between pressured and unpressured states.
