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What is a membrane keypad

Membrane keypad is name membrane switch, it's a custom switch that design with many keys. Many people like to call this as the membrane keypad.

The membrane keypad is a kind of switch which is very popular in the world in recent years. It consists of graphic overlay, upper circuit, isolation layer and lower circuit.


The membrane keypad has the advantages of beautiful appearance, novel appearance, small volume, light weight and strong sealing. With moisture-proof, dust-proof, anti-oil, acid and alkali resistance, seismic and long life-time and so on.

The membrane switch comply with the electromechanical products to the multi-functional, small size, light weight, novel appearance, intensive, intelligent direction of development requirements, Since from the year 1980, the membrane switch has been widely used in Medical instruments, Computer control, Machine control tools, Electronic weighing apparatus, Post, Telecommunications, Copier, Refrigerator, Microwave oven, Fans, Washing machine, Remote control, Electronic game machine and other fields. And, in Intelligent instruments, Electronic weighing apparatus, Office automation, Medical equipment, Household appliances and many other Civil electronic products have been used more often.

By technology points, the membrane switch belongs to the category of screen printing products, but the membrane key is a produce that contain a switch functions, panel decoration, switch connection, circuit tail connect and conventional panel text, graphic symbols as a set. The membrane switch is  from the simply of screen printing products, the membrane switch actually participates in the functional operation of the whole product, and is also the integrate of the electronic product control system.


Product Construction

1. Graphic Overlay

Graphic overlay is build with transparent PET, PC which less than 0.25mm thickness raw material and do the silk printing patterns and text process, Because the graphic overlay is the most important as the identification and keys press, so the selection of materials must have high transparency, high ink adhesion, high elasticity, high flexible and so on.

2. Graphic overlay adhesive

The graphic overlay is used to stick the graphic overlay layer and the circuit layer together, in order to achieve the effect of good sealing and connection, this layer generally requires the thickness of 0.05-0.15mm, with high strength viscosity and anti-aging; During the production,  we need to choose the special professional double-sided adhesive. For some membrane switch request a waterproof and high temperature working,  the graphic overlay adhesive must also be required to use a different properties of materials.

3. Control upper circuit and lower circuit

This layer must build with polyester film (PET) that with good performance as basic, then the printing conductive silver and conductive carbon by a special process. So that it has conductive properties, it's thickness generally within 0.05--0.175mm, the most common is 0.1mm PET.

4. Spacer adhesive

It is between the upper circuit and the lower circuit layer, it can as the sealing and connection between the two layer circuits. It's build with the PET basic and double side adhesive, the thickness of 0.1-0.3mm.  When selecting this layer material, we need to fully considered the overall thickness of the product, insulation, circuit key package handle and sealing.

5. Rear adhesive

The rear adhesive also the double side adhesive, it a kind of material is closely related to the customer terminal enclosure. We are very often used 3M adhesive, Nitto adhesive ad and so on.

The Raw Material

1. Types of Materials

For the membrane switch and the graphic overlay raw material, We not only request of flatness and printing adaptability, but also request to have the characteristics of flexibility and high elasticity.

PVC °C. 175 ~ 0.5 / gloss\ Stable to acids, bases and salts at room temperature. Good abrasion resistance, fire resistance, self-extinguishing, noise dissipation, good electrical insulation. Poor thermal stability. This used more often at low common panels, graphic overlay. But if need a ask a ROHS certification, here

not a suggestion.

Polycarbonate PC\ -60 ~ 120 °C. 175 ~ 1.0\ gloss surface and high transmittance , Low water absorption, good dimensional stability, good bending, good tensile, compressive strength is very superior, good heat resistance, good cold resistance, good electrical insulation and resistance to atmospheric aging. But the material with poor drug resistance, poor fatigue resistance, easy to produce stress cracking, the output interface terminal circuit is mostly with carbon printing, and there is no protective coating, By the air oxidation gradually formed a layer, to the end of the life of the circuit, which is the most vulnerable to failure of the membrane switch, So, choose the PC material mainly determined by the environment, whether used or not, physical damage time is 3-10 years. In general, the PC material application is the most extensive, it can meet the requirements of most membrane switches, also the high light transmittance of glossy PC can catch the requirements which with LCD window.

Polyester (PET)\ -30 ~ 120 °C. 1 ~ 0.2 gloss drug resistance, insoluble in general organic solvents, not alkali resistant. It has excellent mechanical properties, electrical properties, rigidity, hardness and the greatest strength and toughness of thermoplastics, low water absorption, excellent wear resistance, friction resistance, high dimensional stability. The tensile strength was comparable to that of aluminum film and much better than that of PC and PVC. Low cost because the surface is difficult to process into matt type, the textured PET is more expensive but the most substrate to make a good membrane switches. Textured PET also suitable for products with high surface requirements or LCD windows.

2. The thickness of the material

The plastic substrate thickness less than 0.25 mm is called a film, which is mainly used as a graphic overlay of a membrane switch, The printing on the backside with a variety of indicative patterns, text to indicate the corresponding switch key operating area, the thickness option should depend on the enclosure panel and the size of the keys. Choose too thickness material, the touch press feeling increased, and also slow reaction feeling; The material choose is too thin, the touch feeling is poor, the keys rebound also not obvious. Thickness more than 0.25mm called a plate, it's not suitable for three-dimensional key molding, this can be used as a keyless operating area of the indicative plate panel, but also as a film back-plate to improve it's hardness.


Manufacturing process

The mostly membrane switch suggest to build with polycarbonate (PC) film, PVC film, polyester (PET) film. PC film is widely used because of its good mechanical properties, chemical corrosion resistance, temperature resistance. The graphic overlay of the membrane switch use the of screen printing technology,  and printing the text, the symbols, etc on the PC film or the PVC film.

The characters, symbols and transparent windows on the panel have the functions of nominal, decoration and reminding the working status. The production of the screen printing should also take different technological measures.

1. The printing film build of the text

To make the text clear, beautiful, text screen film to have a certain thickness, according to the thickness of the text, the fine text should be slightly choose a thin film, and it can improve the clarity of text; For a thicker text symbols should be slightly thick film, and this can be ensure that the text of the vigorous.

2. Screen printing of transparent windows

The graphic overlay often ask design with a transparent window. From the application point of view, the transparent window should enhance the luminous effect of LED and LCD. The production of its screen film should be used photosensitive glue direct method, the film thickness should be as thin as possible, screen printing should choose monofilament thin screen plate, so that the transparent window of the ink layer thinner and uniform, to ensure the light-emitting element display effect.

Type of switch

The substrate of the circuit should be polyester (polyethylene phthalate) film (PET). It has good insulation and heat resistance, high mechanical strength, transparency and air tightness, especially bending resistance and high elasticity, and is an good material for making the keyboard circuit.

1. Flexible membrane switch

The flexible membrane switch is a typical of membrane switch design. The reason why this kind of membrane keypad is called flexible is that the graphic overlay, the isolation layer and circuit layer of the membrane keyboard are all composed of software films with different properties. The circuit layer of the flexible film keyboard use polyester film (PET), it with good electrical performance as the basic of the switching circuits. Due to the influence of the properties of polyester film, the keyboard has good insulation, heat resistance, bending resistance and high resilience. The graphics of the switch circuit, including the switch's connection and its outlet wire, are printed with low resistance, low temperature curable conductive paint. Therefore, the composition of the entire membrane keyboard has certain flexibility, which is not only suitable for use on a flat enclosure, but also can cooperate with a curved enclosure. The flexible membrane switch circuit tails is integrated with the membrane switch itself. It is collected at a certain place of the film and extended outwards according to the specified position and standard line distance, and connected with the rear circuit of the whole machine as a soft, arbitrarily flexible and sealed circuit tails.

2. Hard film keypad

Hard Film Keypads refer to switches whose graphics and wiring are fabricated on common printed circuit copper clad laminate. The characteristics of rigid membrane switch are easy to obtain material, stable process, low resistance, and can be directly welded on the back of some components of the circuit. In the case of small size, the hard lining layer can be omitted. Rigid film keyboard generally use metal domes as conducting contacts, it has better feel. The disadvantage is that the assembly of the whole machine is not as convenient as the flexible film keyboard, and it is necessary to solder the plug-in and use flat cable wire. The rigid membrane switch have the bounce sounds feedback, LED indication, generally may use the metal feeling.

3. The flat membrane switch

The keys on the membrane switch with different colors, indicate the position, shape and size of the key body. Three-dimensional membrane keyboard: Normally, the keys on a membrane switch only use color to show the position, shape and size of the keys button. In this way, the accuracy of the operation can only be identified by the operator's vision, because there is no appropriate feedback to indicate whether the finger is pressed in the effective range of the switch, which affects the confidence of the whole machine monitoring and the speed of operation. The utility model relates to a membrane switch which makes the key button slightly convex, slightly higher than the panel, and forms a three-dimensional shape, called a three-dimensional key switch. The solid key can not only accurately give the range of the key button, improve the recognition speed, make the operator's tactile more sensitive, but also enhance the appearance of the decorative effect of the product. For the three-dimensional key switch , the height of the three-dimensional convex generally is better not exceed twice the thickness of the substrate. The bulge of the bulged film membrane switch can be varied for the appearance of the beautiful product.


The Advantages of Membrane Switch

1. Beautiful appearance and novel;

2. Small size, thin thickness, light weight, more conducive to high intelligent direction.

3. Moisture-proof, dust-proof, anti-oil and harmful gas, strong sealing, acid and alkali resistance earthquake.

4. Long lifetime, bending resistance.


Application field

1. Industrial field: widely used in intelligent electronic measuring instruments and meters, computer control, digital machine tools, industrial controllers, industrial scales and so on. Industrial control membrane switch.

2. Household appliances: widely used in air conditioning, washing machine, induction cooker, microwave oven, rice cooker, soybean milk machine, etc.

3. Medical equipment field: widely used in fitness equipment, electronic sphygmomanometer, a variety of therapeutic instruments, etc.


The New Technology of Membrane Switch

1. Screen printing for isolation layer

The structure of the membrane switch request that the two circuits must have a layer of isolation layer, which as the separating circuit layer, controlling switch stroke and conducting air flow. The traditional isolation layer adopts insulating film, and at now, most of them use screen printing point rubber particles to replace the isolation layer, that is, between the upper and lower circuits, the screen printing layer has a viscous latex with high tension and high elasticity, so that the upper and lower circuits can be isolated. The process not only produce easier, but also has advantages in transparent circuits.

2. Introduction of flexible circuit board technology

With the application of high performance flexible resistance welding ink, the flexible printed circuit board technology based on polyimide copper foil and polyester copper foil is becoming more and more mature, which makes the performance of membrane switch improved too much. In the traditional membrane switches, the metal material of the thin film circuit is mainly silver ink, and the screen printing technology is used to make it converge on the thin film. The contact resistance of the circuit is large, generally 0.5 mhOM/ square (resistance per unit square). The connection between the tail circuits and the connector is crimped or plugged in. The contact resistance can be too much reduced by combining the thin film with the flexible circuit board, and the circuit with one side and two sides flexible circuit board as the membrane switch can much reduce the contact resistance. The connection of the rear circuit can be riveted, connected and welded, which greatly improves the reliability of the thin film button.

3. Electrostatic shielding technology

The membrane switch have replaced the traditional mechanical keyboard and are widely used in mechanical and electrical instruments and instruments. Because of this, a layer of conductive metal material (usually using the mixture of silver paste and carbon pulp) is printed on the panel of membrane switches, which is connected to the GND. The electrostatic charge on the surface of plastic film can be effectively grounded through the GND to have the electrostatic shielding performance, and can be applied to instruments and instruments in flammable and explosive environment such as coal mine.

4. Multifunctional integration

The traditional switch only used as switch function of on and off, and the function is single. The membrane switch design can refer to the requirements of instruments and instruments, the mounting electronic components (including mount resistance and capacitance elements, inductance elements, light-emitting devices, vocal devices, etc.) have been applied to membrane switches, and a new type of light-saving and fluorescent ink has been applied. So that the film button collection switch, decoration, conventional panel note, luminous display, voice prompt and other functions in one, to achieve some circuit board functions.


Current Situation and Future Development Trend of Membrane Switch  Market

The global membrane switch market reached sales of USD 640 million in 2021 and is expected to reach USD 740 million by 2028 at a compound annual growth rate (CAGR) of 2.1% (2022-2028). At the regional level, the Chinese market has changed rapidly in the past few years. The major global membrane switch manufacturers are Molex, Fujikura and so on, the world's top two membrane keypad manufacturers together occupy more than 15% of the market share.

Asia Pacific is currently the largest membrane switch market in the world with about 55% market share, followed by the US and Europe with a combined share of over 40%.


Major membrane keypad suppliers include:

Molex

Fujikura

Nelson-Miller

Dyna-Graphics Corporation

AMP