What Is A Membrane Switch?
The membrane switch is an operating system that integrates key functions, indicating components, and instrument panels. It consists of four parts: panel, upper circuit, isolation layer, and lower circuit. When the membrane switch is pressed, the contacts of the upper circuit deform downwards and make contact with the plates of the lower circuit. After releasing the finger, the contacts of the upper circuit rebound back, the circuit is disconnected, and the circuit triggers a signal. The membrane switch has a rigorous structure, beautiful appearance, and good sealing performance. It has the characteristics of moisture resistance and long service life. It is widely used in electronic communications, electronic measuring instruments, industrial control, medical equipment, the automobile industry, smart toys, household appliances, and other fields.
A membrane switch, also known as a Tactile Membrane Switch, adopts an overall sealing structure composed of flat multi-layers. It is a kind of optical, mechanical, and electrical integration that seals the key switch, panel, mark, symbol display, and lining together. New electronic components are a fundamental change in the appearance and structure of electronic products. They can replace the buttons of conventional discrete components and perform operating system tasks more reliably.
Membrane switches are waterproof, dustproof, oil-proof, harmful gas corrosion resistant, stable and reliable performance, lightweight, small in size, long life, easy assembly, and assembly, the panel can be washed without the characters being damaged, rich colors, beautiful appearance, etc. advantage. Use membrane switches to make your products more contemporary. The main type of membrane switch is a membrane switch panel, which is made of a rigid or flexible printed circuit board as a base, installed with touch or non-touch buttons, and then covered with plastic (polycarbonate PC, polyester PET) printed with colorful decorative patterns. etc.) is an electronic component composed of a thin film panel that integrates switching functions and decorative functions. It is a new type of human-computer dialogue interface. The connection between the switch circuit and the whole machine can be accomplished by welding or plugging.
Types of Membrane Switches
Membrane switches is a user interface that is often used in various electronic devices and control panels. They are composed of multiple layers of flexible materials, including a top graphic cover layer with printed symbols or labels, a spacer layer, and a bottom membrane layer with conductive traces. When the user presses the button on the graphic overlay, it bends and makes contact with the conductive traces on the bottom membrane, forming a circuit and recording the button press. There are many types of membrane switches, including：
Non-tactile membrane switches
The non-tactile membrane switch does not provide tactile feedback or a physical “click” sound when pressed. They are usually used in applications that require a soft touch.
Tactile membrane switches
The tactile membrane switch is designed to provide feedback to the user when the button is pressed. They usually have a dome or a protrusion on the bottom membrane. When the button is pressed, the dome or protrusion will collapse or make a click, giving the user tactile feedback.
Membrane switch with metal dome
Metal dome membrane switches use one or more small metal domes as tactile elements. When the dome is compressed, it provides unique tactile and sound feedback. These are usually used in applications that require crisp button presses.
(a) Membrane switch type:
It is the most basic and most commonly used structure. The tactile dome acts as both a tactile and a circuit.；
(b) Membrane switches type:
The structure type is complex, and it is used in situations where there are more tactile domes and there are no jumpers. The tactile domes are placed on the upper and lower circuits. The conductive surfaces of the upper and lower circuits are all upward, and the upper circuits need to be punched.When this structure is turned on, the four feet of the dome are not in the same plane as the center point, and there are “two stages”.At the same time, the tactile dome is often in an overly concave state. After a long time, the tactile dome will not rebound. It is not recommended to use it;
(c) Membrane switches type:
The tactile dome is placed on the upper circuit and only plays the role of tactile. The upper circuit conducts electricity and faces down, and the lower circuit conducts electricity and faces up. In the case of “two stages”, it is not recommended to use it.；
(d) Membrane switch type:
The tactile dome is placed on the lower circuit, and there are traces on the upper and lower circuits. The tactile dome not only plays the role of tactile, but also plays the role of connecting the upper and lower circuits; It is used for occasions where there are more shrapnel, denser, and no jumpers are required. (b) The membrane switch type has a simple structure type.When designing, pay attention to the line routing to avoid the four legs of the tactile dome to ensure that there is no short circuit.
Polymer membrane switch
The Polydome membrane switch uses a polymer dome as a tactile element. These domes are made of flexible plastic and provide tactile feedback similar to metal dome switches but at a cheaper price.
LED backlight membrane switch
The LED backlit membrane switch uses LED (light-emitting diode) lighting under the graphic overlay to illuminate the button or label and make it visible in low light conditions. They are usually used for control panels and equipment that require a backlight to improve visibility.
(a) The LED line is on the same layer as the lower line:
The structure is simple, but if the selected LED light is of a higher height, the LED light will lift the panel. At this time, the LED window on the panel should be convex, or the thickness of the adhesive layer should be thickened to make its thickness greater than the thickness of the LED light.；
(b) The LED line has different layers from the lower line:
The structure is complex, but the LED window does not have to be convex, but the upper area of the LED light must be hollowed out to prevent light from passing through the LED light hole. Note: At this time, when the circuit is offline, avoid the wiring around the LED light hole.
Capacitive membrane switch
Capacitive membrane switches do not have physical moving parts like traditional membrane switches. Instead, they rely on changes in capacitance to detect when the user’s finger approaches or touches the button. They are usually used in applications that require touch-sensitive and stylish design.
Sealed or waterproof membrane switch
Sealed or waterproof membrane switches are designed to withstand moisture, dust, and other environmental factors. They are usually used in outdoor or industrial applications that need to be protected from natural factors.
Custom membrane switch
Custom membrane switches can be custom according to specific design requirements, including the number of buttons, layout, graphic design, and tactile feedback. Shanyo manufacturers can manufacture membrane switches to meet the unique needs of various applications.
Benefits of membrane switch keyboard
Membrane switch keyboard are used in a wide variety of applications, whether domestic, commercial, or industrial. Other types and forms of user interface include touch screens, keypads, switches, and selector knobs. However, membrane switches are preferred due to their compact size, simple construction, high reliability, resistance to harmful elements, and low cost. These advantages are further elaborated below.
Durability
The service life of a membrane switch can generally reach more than one million times. Although the elastic membrane has crept one million times, the extent of the creep is very small, but it is far from reaching the yield limit of the film, so the membrane material can withstand one million times. Above life span without deformation. On the other hand, the contacts of the switch are in vertical contact and wear very little.
Good sealing
Since the Membrane switch keyboard has an overall sealed structure, the contacts of the switch are not corroded by harmful gases, are not easily oxidized, and are waterproof and dustproof, making them more suitable for various harsh environments.
Small size, lightweight, and reliable structure
Membrane switch keyboard are designed to be arranged and combined to form a membrane keyboard and are composed of multiple layers of membranes. The connections and lead-out lines between all switches are completed at one time by screen printing. The total thickness is generally less than 1mm, so it has reduced volume, reduced weight, and improved reliability.
Rich colors and beautiful appearance
Button membrane switch according to the user’s design concept, the color and pattern design reflect individuality, and the decorative effect reflects the comprehensive characteristics of material beauty, decoration beauty, and craftsmanship beauty. The preparation process for graphic overlays is simple. Membrane switch keyboard are composed of multiple layers of thin plastic material, each layer contributing to its overall slim design. These overlays typically include graphic overlays, spacer layers, and printed circuit layers. The graphic overlay is usually made from polyester or polycarbonate, and the spacer layer is usually made from a flexible insulating material such as silicone with minimal thickness. This stylish and low-profile design makes the membrane switch ideal for aesthetics, space efficiency, and durability. applications where safety is critical, such as medical equipment, industrial control panels, and consumer electronics.
Easy to clean and maintain
Membrane switches are typically designed with a flat sealing surface that prevents the ingress of dust, dirt, and liquids, making them highly resistant to environmental hazards. Cleaning membrane switches is a simple process; users simply wipe the surface with a damp cloth or mild cleaning solution without worrying about damaging delicate components. Its durable construction ensures longevity and can withstand frequent cleaning without wear or degradation. This low-maintenance feature makes membrane switches the first choice for industrial applications where cleanliness and reliability are important, such as medical equipment, industrial control panels, and consumer electronics.
Sufficient tactile feedback
Membrane switches are designed to provide users with a unique and reassuring tactile feel when pressed, ensuring they know their input has been registered. This feedback not only increases user confidence in interacting with the device, it also helps prevent accidental key presses. Tactile feedback in membrane switches is typically achieved through the use of domes or other deformable structures within the switch membrane layer. These structures allow users to feel a distinct “click” or resistance when pressing keys, making it easier to type accurately and comfortably on the keyboard or operate various controls.
Excellent electrical conductivity
The circuit of the switch can be printed with carbon paste, silver paste, copper platinum, etc., and the conductive layer can be folded at will; and the resistance can be controlled at any resistance you want, and using unique technology, the membrane switch made can even accept A high-voltage electric shock of hundreds of thousands of volts without damaging its function.
Long service life
Because the materials used in membrane switches have good insulation, heat resistance, bending resistance and high resilience; and the patterns are printed on the reverse side, so that the silk screen pattern will not be damaged; therefore, the membrane switch has a normal service life. It can last more than three years.
Shield electromagnetic interference
Unwanted electromagnetic frequencies and electrostatic discharge are potential threats to electronic equipment. These can cause electronic equipment to malfunction, especially controllers using low-power circuits. A layer of EMF shielding can be added to the membrane switch by printing a grid or mesh with conductive ink. EMF shielding can be made without any discontinuities, which defeats the purpose or reduces the effectiveness of the shielding.
Low cost
Due to their smaller blueprints and easy availability of building materials, membrane switches are more economical than touch screens or mechanical interfaces. This cost-effectiveness results from its simple design and efficient manufacturing process. Unlike traditional mechanical switches that involve complex components, membrane switches are composed of thin layers of flexible materials (including PC or PET) and printed conductive circuits. This simplified structure not only reduces material costs but also minimizes assembly expenses. Additionally, ease of customization and mass production further enhance their economics.
After tearing off the release paper, it can be firmly stuck on the surface of the whole machine. Its lead wire can be inserted into the socket of the rear circuit of the whole machine, and the circuit can be connected instantly. Saving labor and materials reduces the supporting cost of the whole machine.
Membrane switch panel Construction
Membrane switch panel are assembled from multiple components in layers using pressure-sensitive adhesive or heat-sealable film. Its main parts are the overlay that contains the graphic elements; the circuit, including the conductive tracks, metal domes, circuit tails, and terminals; and the spacers that maintain the disconnection between the switch contacts.
Membrane switch panel Overlay
The panel layer of the flexible membrane switch is generally made of colorless transparent sheets less than 0.25MM, such as PET and PC, silk-printed with exquisite patterns and text. Since the main function of the panel layer is to function as a logo and button, the material must be selected. It has the characteristics of high transparency, high ink adhesion, high elasticity, and high toughness. There are two commonly used materials for making covering layers.
Material selection for membrane switches
Panel material
Generally divided into two categories: PC (Polycarbonate) and PET (Polyester).
PC
- There are bright and matte surfaces (fine sand, medium sand, coarse sand)
- Commonly used thicknesses are 0.125, 0.175, 0.25mm
- Special treatment includes HP series (such as HP40, HP60 and HP92S, etc.)
- Advantages of PC material: good ink adhesion.
- Disadvantages of PC material: poor corrosion resistance, difficult to use in outdoor products.
- Generally, those with windows use glossy PC, and those without windows use matte PC. Matte PC is scratch-resistant.
PET
There are bright and matte surfaces:
- Matte: Autotype (thickness 0.15mm and 0.20mm)
Kimoto (thickness 0.125mm and 0.188mm)
- Glossy side: Autotype (thickness 0.18mm and 0.25mm)
Lzaya (thickness 0.125mm and 0.188mm)
The above PET is all processed PET.
- Autotype PET has excellent adhesion to ink. Its material molecular structure has a combination of softness and rigidity, and has good appearance and dimensional stability.
- Advantages of PET materials: good corrosion resistance, resistance to harsh environments, bending resistance, good temperature resistance, and good elasticity.
- Disadvantages of PET materials: Compared with PC materials, the adhesion of ink is slightly worse.
- Matte PET is scratch-resistant.PET material has a tactile embossing feel, while PC material embossing has a relatively poor tactile feel. Under normal circumstances, thin materials are used when the panel is not embossed, thick materials are used when embossing, thin materials are used when upper lines are embossed, and thin materials are used for products with elastic sheets. All of these are for the good feel of the membrane switch.
Membrane Switch Metal Dome
The dome is the component that provides tactile feedback. They can be made of metal or plastic. The size of the membrane switch key determines the size of the dome, which ranges from 0.24 to 0.79 inches (6 to 20 mm). Additionally, the height of the dome is closely related to the size of the dome, which can be 0.010 to 0.057 inches (0.25 to 1.45 mm).
A critical aspect of using a dome is the actuation or triggering force required to depress the dome and actuate the switch, which can range from 1.41 ounces to 80 ounces (40 to 2250 grams). Domes come in many shapes and sizes, including:
- four legs
- triangle
- round
- rectangle
metal dome
Metal domes are made of stainless steel or copper alloy and are held in place by dome retaining layers or spacer layers. In addition to providing tactile feedback, the metal dome also acts as part of an electrical circuit. When pressed, the metal dome shorts the open contact of the switch. Metal domes have a very low profile and are rated to last up to 10 million compressions, making them ideal for many applications.
Surface glue layer
The main function of the surface glue is to closely connect the panel layer and the circuit layer to achieve sealing and connection effects. This layer generally requires a thickness between 0.05mm – 0.15mm, with high viscosity and anti-aging properties; during production, a special membrane switch double-sided tape is used. Some membrane switches require waterproofing and high-temperature resistance, so the surface tape must also use materials of different properties according to needs.
Control circuit upper and lower layers
This layer uses polyester film (PET) with good performance as the carrier of the switch circuit pattern and uses a special process to screen-print conductive silver paste and conductive carbon paste to make it conductive. Its thickness is generally 0.05– Within 0.175MM, the most common one is 0.125MM PET.
Circuit material:
PET has good insulation and heat resistance, high mechanical strength, transparency, especially bending resistance, and high elasticity. Therefore, PET is an ideal material for making membrane switch circuits.
- Generally, untreated PET is used
- Thickness is 0.075, 0.1, 0.125mm.
- It is generally appropriate to choose 0.125mm. If it is too thick, the response will be slow and the switch sensitivity will be poor. If it is too thin, it will have insufficient elasticity and will not be conducive to the plug-in of the lead wire end.
Circuit layer
This layer is where the switch conductive path is applied. Conductive paths can be created by screen printing and photochemical etching.
Screen Printing:
This method uses a template that contains a circuit pattern. Silver conductive ink is submerged onto a template placed above a substrate. The substrate used is usually polyester film. This method is used for thinner and more flexible membrane keyboards.
Screen printing:
Photochemical Etching: In contrast, this method uses a copper laminate substrate that is selectively patterned by photolithography and chemical etching. The result can be a printed circuit board (PCB) or flexible printed circuit (FPC) that is thicker and more durable than a screen-printed membrane keyboard.
Photochemical etching
Depending on the type of membrane switch, the circuit can be designed and constructed in two ways.
Two-layer circuit:
the circuit layer is divided into an upper-layer circuit and a lower-layer circuit. Each circuit layer contains a conductive path that leads to or from the switch. A spacer layer separates the two levels. When the switch is pressed, the upper circuit deflects and contacts the lower circuit, completing the circuit.
Single layer or single sided circuit:
A single-layer switch has only one layer of circuitry. Discontinuities cause circuit interruptions in the conductive paths printed onto the substrate. The circuit is accomplished using a metal dome or conductive ink printed on the back of a plastic dome. When the button is pressed, the dome flattens the circuit layer, creating a single conductive path.
End of circuit
The circuit tail is the part of the circuit that connects the membrane switch to the machine control unit. It is a flat, flexible tape consisting of multiple conductive tracks printed on polyester tape. The circuit tail ends with a standard connector that mates to the control unit’s terminal block. Common connector options are regular connectors, latching connectors, or solder tabs.
Laminated layer
It is between the upper circuit and the lower circuit layer and plays the role of sealing and connection. Generally, PET double-sided tape is used, and its thickness ranges from 0.05 to 0.2MM. When selecting the material for this layer, the overall product should be fully considered. Thickness, insulation, circuit button bag feel, and sealing.
Back adhesive layer
The use of adhesive tape is closely related to what kind of material the membrane switch is attached to. Commonly used ones include ordinary double-sided tape, 3M tape, waterproof tape, etc.
Membrane switch spacer (isolation layer) material:
Generally 0.1, 0.15, 0.20, and 0.25mm thick double-sided tape.
The thickness of the membrane switch spacer on the size and shape of the key, which is directly related to the operating pressure of the membrane switch and the sensitivity and reliability of the switch. Therefore, the size of the keyhole should be consistent with the size of the key pattern. When the size of the keyhole is larger, the thickness of the keysheet will also increase.
Membrane switch keyboard spacer ventilation slot
- For the key sheet, in addition to punching the key sheet hole, it is also necessary to process the air guide groove, that is, the ventilation groove.
The function of the ventilation groove is to conduct the air sealed in the membrane switch. The design of the ventilation slot is not arbitrary. It should be based on the relationship between adjacent key positions and the amount of air absorbed by the keyhole to determine the direction of the shunt. This way, we can better use aerodynamic force to force the relevant key positions to reliably separate.
- The ventilation slot is generally 2mm wide, and there are no less than 3 keyholes connected to the ventilation slots, and 4-6 key connections provide better results. If the number of keys is less than 3, the key ventilation slot must be ventilated to the outside. It is ventilated to the outside and the buttons feel good to the touch.
- The minimum line width is 0.3mm, generally 0.8-1.0mm.
- The line routing should generally be within 2mm of one side of the line shape.
- The circuit shape is generally 0.5mm smaller on one side than the panel shape (easy to assemble).
- The finger area of the lead wire needs to be covered with silver paste with carbon paste.
Carbon paste is a non-metallic conductor paste that does not combine with oxygen in the air and can protect the underlying silver paste from oxidation. Carbon also has high wear resistance, which is convenient for plugging and unplugging leads and connection terminals.
Inks
Divided into conductive ink, insulating ink, matte ink, and color ink.
1. Conductive ink: silver paste, carbon paste, and silver-carbon mixed paste
2. Insulating ink: plays an insulating role and is generally used for jumper insulation and entire surface insulation.
3. Matting ink: window matting, panel matting
4. Color ink: Due to different materials, the inks used are also different. They are divided into inks for PC materials and inks for PET materials.