Membrane switches

A total of 15,000—17,000 t of resin is used aimuaHy. Polycarbonate also has many technical uses in instmment panels and devices, especiaHy for membrane switches and insulators. Optical quaHty polycarbonate is the only suitable material for the compact disk market. Since their introduction in 1983, compact disks have shown explosive growth in the consumption of polycarbonate, with utiHty for audio, video, and computer appHcations. Consumption of optical quaHty resin more than doubled between 1988 and 1992, and as of 1995 accounted for about 20,000 t of annual production. 

Polymer thick films also perform conductor, resistor, and dielectric functions, but here the polymeric resias remain an iategral part after cuting. Owiag to the relatively low (120—165°C) processiag temperatures, both plastic and ceramic substrates can be used, lea ding to overall low costs ia materials and fabrication. A common conductive composition for flexible membrane switches ia touch keyboards uses fine silver particles ia a thermoplastic or thermoset polymeric biader. 

Membrane Switch Assembly Laminating Adhesive Films... 

Fig. 18. Transfer tape use in membrane switch assembly. (On right liner is removed, leaving die cut PSA ready for placement of laminate on the left.)...

Common applications for transfer tapes include the assembly of membrane switches used in the electronic industry, the attachment of face plates to appliances and other equipment, the assembly of automotive displays in the in.strument cluster, and the assembly of displays, such as touch screens for computers and teller machines. Fig. 18 pictures the use of a transfer tape adhesive in the assembly of a membrane switch. 

Screen 10K-100K 25 50-100 Membrane switch, label printing... 

Electrical measurements with purified, reconstituted Na+ channels have demonstrated that an individual channel can exist in either conductive or nonconductive states. As shown in figure SI.4, the fraction of time that a channel spends in the conductive state depends strongly on Ai//, increasing abruptly as A iff is made less negative. These results agree well with the notion that a local depolarization of the plasma membrane switches the nearby Na+ channels to their conductive states and thus launches an action potential that propagates down the cell. 

Standard Test Method for Silver Migration for Membrane Switch Circuitry, ASTM F1996-01, Am Soc. Testing and Materials. 2003. 

Step 3 When the hydrogel membrane becomes sufficiently charged, the membrane switches back to its swollen, high permeability state. The system is now poised at Step 1, and the cycle repeats. 

For many applications, especially in the automotive industry, precision parts can only be mass-produced competitively and cost-effectively by using liquid silicone rubber. Successful applications include seals, 0-rings, membranes including central locking membranes, switch... 

Electronic tapes Membrane switches Ceramic binders Conformal coating... 

Electrical, electronic, and technical applications use polycarbonates for a variety of purposes. The worldwide market is about 160,000 t annually. Because of excellent electrical properties (dielectric strength, volume resistivity) and resistance to heat and humidity, polycarbonate is used for electrical connectors, telephone network devices, outlet boxes, etc. Polycarbonate had been popular for use in computer and business machine housings, but the use of neat resin was largely supplanted by blends of polycarbonate with ABS. However, new, highly colored and special effect resins (translucents, flip-flop colors, speckles, etc) have recaptured a significant portion of that market. A total of 25,000-30,0001 of resin is used annually. Polycarbonate also has many technical uses in instrument panels and devices, especially for membrane switches and insulators. Optical quality polycarbonate is the only suitable material for the compact disc market. Since their introduction in 1983, compact discs have shown explosive growth in the consumption of polycarbonate, with utility for audio, video, and computer applications, reaching about 25,0001 of annual production. 

The hard-coat layer is scratch and chemical resistant though it can easily be embossed to produce tactile membrane switch domes. These can be selectively varnished to produce windows or specific graphical effects. The film itself has a total luminous transmission of 92% plus an excellent flex modulus and, according to the manufacturers, it has a typical tactile membrane switch dome life in excess of five million cycles. 

Extreme operating conditions call for heavy duty materials, a case in point being the membrane switch material required for the ocean going yacht made by Tiara for which Autotype s Autotex XE (Extreme Environment) hard coated polyester film was used. Unlike traditional substrate materials Autotex XE can withstand high light levels, 85 °C operating temperatures and humidity levels of 85% relative humidity. Conventional films might delaminate, become brittle or flake under extreme conditions. Autotex XE film is polyester-based with specially constructed hardcoat and primer layers. 

Electroluminescent displays are made in Wales by Pelikon at its Cardiff plant where the company specialise in control panel displays. These thin plastic electroluminescent displays comprise a series of segments, each of which is a hidden membrane switch which is identified by an icon above the area of contact. Multi-function touch regions can be incorporated as well a capacitive touch on/off facility. Target markets include the white goods domestic appliance sector. 

PEEK film finds uses as a substrate for flexible printed circuit boards. Mitsubishi has developed a blend of PEEK and polyetherimide (PEI) in which the slow crystallisation characteristics can be utilised to fuse layers of circuit without the need for adhesives. This is a potentially low-cost route to multilayer circuits [14]. Film can also provide a useful moisture barrier in applications such as membrane switches. There are also a number of niche applications such as environmentally resistant RFID tags. 

Membrane switch - film Golden Valley Products Moisture barrier, chemical and temperature resistance... 

There are several different constrnctions for keypads on flexible circuits. Thick-film circuits on polyester film called membrane switch could be a low-cost solution with many millions of reliable contacts. The basic mechanism of the switching is illustrated in Fig. 64.25. Generally, the membrane switches are connected through FFC connectors to the main circuit board. Polyimide-based circuits are necessary with soldering of components. 

The membrane switches built on polyester film are widely used as the standard keyboard circuits of personal computers. They are also used as the switching components of touch panel boards for home appliances such as microwave ovens and office machines such as copy machines. They are also used with the touch screens of display devices. 

The largest apphcation of thick-film-based flexible circuits is in membrane switches, which need large circuit spaces but do not carry large currents. The majority of membrane switches are covered by silver paste thick-fihn flexible circuits. Major switching circuits of keyboard switches are also covered by the same constructions. Most of the key board circuits are covered by the silver paste base membrane switches. Most of the touch panel switches designed for micro waves, office appliances and medical equipment also use PET based membrane switches. Several examples are shown in Fig. 66.13. 

FIGURE 66.13 Membrane switch made by thick film process. 

Fig. 3.12. Microcomputer keypad made from a single moulding of a liquid silicone rubber, with its underlying membrane switching circuit. (Sinclair Research, Haffenden and NFI Electronics.)...

Leaders in the design and manufacture of metal-dome switch contacts and complementary equipment for membrane switches and related mechanical-switch industries are seeing higher demand. This, in turn, is increasing the need for fully automated high-speed production methods. 

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