1. Membrane Switch Definition
As we all know, membrane switch is a kind of human machine interface. It’s an electronic part that integrates functions of switch and decoration. But, it is different from the mechanical switch. In general, the latter is made of copper and plastic parts. While, the membrane switch is a circuit printed on PET or other material. Always, the ink for screen printing is copper, silver or graphite, so it conducts electricity.
This switch is a user interface tool, which connects users’ commands and electronic devices. And we can consider it as a tool like other types of the control system, such as touch screen, plastic keyboard, and toggle switch. The user interface utility can be simple like an on-off tactile switch, or be complex like membrane keyboard and graphic interface used with a computer.
2. Types of membrane switches, pros, and cons
The main eight different types of membrane switches include these as below.
2.1 Metal dome type
It uses metal domes as the conducting medium.
Advantages: Firstly, the keys have good tactile feedback. Also, the strength is uniform, and stroke accuracy is high.Secondly, you can hear a crisp sound during pressing control panel overlays and clearly understand the operation situation. As a result, it avoids repeated operations due to the buffer time of some equipment.Thirdly, its usage temperature can reach -20 ～ 80 ℃.
Disadvantages: When the lining board is uneven or pasted in a large bending arc, it may cause short circuit, malfunction and non-rebound of domes.
Suggestion: Use them on a flat liner that can withstand the strength of the keys. Or directly use a thick PCB (printed circuit boards) as the circuit layer.
2.2 Hot pressing convex type with tactile feedback
Screen print the graphic overlay material and roll up bump to form a rebound force.
Advantage: Firstly, it has high life, which can reach more than 500,000 times. Secondly, it feels good, membrane switch manufacturers can customize the stroke and intensity according to customers’ needs.
Disadvantages: Firstly, the cost of the mold is high, and it is necessary to open the convex mold. Secondly, using in high temperature environment may cause the key force to weaken.
Suggestion: We can open metal mold for the convex graphic overlay to ensure the consistency of the button strength and stroke.
2.3 Flat touch type
A membrane switch manufacturer uses the overlay material to print the electrical conductor in the point of contact. And it does not use the secondary process.
Advantages: Firstly, the key life of switch panels is high and can reach one million times. Secondly, the contact area is large to ensure the conduction rate.
Disadvantages: There is no operation feel, and it’s easy to cause repeated operation or misoperation.
Suggestion: We can enlarge the spacing between keys as much as possible. Otherwise, it will increase the failure rate and reduce the life.
2.4 Capacitive type
Capacitance induction type: The use of a conductive body to induce conduction.
Advantages: Firstly, it can sense action at a certain distance like a capacitive touch screen. Secondly, we HuaiSong Industrial can design the sensing distance according to the customer’s needs.
Disadvantages: Firstly, it is sensitive to ambient electromagnetic interference. And the design requirement is pretty high. Secondly, it needs supports of related electronic components and chip.
2.5 LED light type
Based on the ordinary membrane switch, insert a guide plate allows the product to be used in places with insufficient lighting.
Advantages: Firstly, products have a high-end and atmospheric appearance. And we can customize the transparent parts of control panels. Secondly, it’s easy to operate even in a poorly lit area. Thirdly, membrane switch manufacturer makes custom PMS colors for customers. A wide variety of colors in Pantone can be designed and manufactured.
Disadvantages: Due to the limit of the astigmatism of the light guide plate, this type of membrane switch is thick. In general, their thickness is between 2.5mm and 3.5mm.
2.6 EL cold light type
This type of switch is formed by inserting an EL cold light source in custom membrane switch.
Advantages: Firstly, compared with the LED light guide plate type, the thickness is greatly reduced. And its overall thickness is between 1.5mm and 2mm. Secondly, the cold light source is suitable for the normally open state. There is no need to consider the heating problem. Thirdly, we can customize light display windows and PMS color according to customers’ needs.
Disadvantage: A cold light source needs to be equipped with a drive.
2.7 PCB circuit type
Replace the screen printed membrane circuit layer with printed circuit boards(PCB).
Advantages: Firstly, PCB circuit has high precision. It’s firmer, more reliable and has lower resistance value to weld surface mount LED. Secondly, the thickened PCB circuit layer can be directly used as a lining board.
Disadvantage: PCB is a kind of rigid raw material and cannot be bent.
2.8 FPC circuit type
Using flexible circuits in the switch panels circuit layer.
Advantages: Firstly, like PCB, flex circuits also have high precision. It’s firm and reliable to weld LED, too. Secondly, not like PCB, copper flex circuits can withstand bending. This high quality raw material is ideal since it has two benefits of high precision and flexibility.
Disadvantage: The only disadvantage of FPC is its high cost and more quantity required.
3. Graphic overlay materials
The 4 main materials of graphic overlays include polyvinyl chloride, polythene, polyesters and polycarbonates.
First of all, the usage temperature range of the PC material is extremely large (-135 ～ 135 ℃). When the temperature or humidity changes, its performance does not change much. Thus, it ensures that the switch panel can meet some certain application requirements and even be used in some industrial control equipment which are under harsh environment.
Secondly, the PVC has poor temperature resistance. Especially in high temperature over 59℃, it starts to soften. Also, its elasticity is not as good as that of PC. But, it has a high elongation of 130%. Besides, it’s relatively cheap. Therefore, manufacturer of membrane keypads always use it under general conditions.
Thirdly, the heat stabilized polyester has good elasticity and temperature resistance. And its price is between that of PC and PVC. But the surface of raw material is difficult to be processed into a matte texture, and it’s mostly transparent. At the same time, for most plastic inks, if use them to get polyester printed, it’s hard to get satisfactory affect. In general, graphic overlay manufacturers need to use special and exclusive inks.
Last but not least, PE has good physical properties and chemical properties. It can resist a wide variety of chemicals, such as alcohols, aliphatic hydrocarbons, esters and others. But it’s more expensive.
4. Manufacturing key points
How to product high quality custom membrane switches? Of course, the process should be pretty strict, especially the printing processes.
Raw materials for making membrane keypads can’t be replaced by ordinary membrane panels. It must have high transparency and high smoothness, also the softness is important. Generally, the thickness of custom graphic overlay is within 0.25mm. It must never exceed 0.25mm, otherwise, it won’t be called overlay but sheet. Besides, if the overlay materials are too thick, the contact force will increase, and the reaction will become dull. However, materials also can’t be too thin. It will result in poor hand feeling, no obvious rebound, and reduced life. For overlay printing, it has several processes depending on overlay colors. To make one color in user interfaces, we need to screen print one time.
Also, there is a high demand of conductive silver ink for printed circuits. In a general way, the overlay material is thin and has a high surface smoothness. So the conductive silver ink must has a super high adsorption capacity. If the adsorption is not strong, after a while, the circuit is easy to fall off. Membrane switches are high-precision products and have high requirements for circuits. When printing a circuit, it must not be too wide. We should seal the screen printed circuits to avoid its oxidation.
Membrane switches constructed five layers in order to make them work better. As we all know, the top layer of a membrane switch is graphic overlay. Then, overlay adhesive, upper and lower circuits, adhesive separator and back adhesive. During the membrane switch assembly of layer by layer, we need to pay more attention. There can be no pores between layers. Because if there are pores, the silver paste circuit sandwiched in the middle layer will oxidize.
5. Membrane keypads features
5.1 Long life
The working life of a membrane keypad is tens of times that of an ordinary mechanical switch. Generally speaking, the life of the membrane switch is more than 1 million times. Because this value is enough to match the working life of the other components of the machine. Someone has conducted a simulation test on the life of the membrane keypad under rated conditions. The result is that no premature aging or failure occurred even after 3 million times operation or more. Its life can reach such a long time due to the simple membrane switch structured parts. It does not have matching parts like the mechanical switch, but has a single operation principle. Also, its working stroke is short, only 0.10 ~ 0.4 mm. Besides, the contacts are sealed and less affected by external media.
5.2 Small size and light weight
The membrane switch assembly system generally has a total thickness between 1.0 and 1.5 mm. it is only equivalent to the thickness of an ordinary aluminum panel.
5.3 Good tightness
Membrane switch constructed with five layers is integral sealed. Therefore, it is especially capable of preventing fire, dust, explosion, and harmful gases. We can adopt it to work under extremely harsh environmental conditions. For example, used for control panels of electrostatic copiers, we can prevent short circuit caused by charged toner from entering the switch. Membrane keypads in washing machines can withstand various hazards caused by humidity. Also, someone uses them in mining, textile, and high-density dust occasions. Because it can prevent combustion and explosion caused by sparks generated by switching operations.
5.4 Good decoration
The appearance of membrane keyboard is a matte color tone with a diffuse emission. Usually, the surface is soft and is conducive to the protection of vision. Therefore, it’s good for monitoring the instrument. The overlay printing adopts screen mesh, but not digital printing. You can choose any PMS color of the ink, our engineer will do the color matching. There are rich colors to choose to get the required decorative effect. So it can get a harmonious cooperation with the machine modeling and using environment.
Designers can set the text or graphics of the function mark on the key of a function for membrane switch design. Then, it can improve the recognition accuracy and discrimination speed. All graphics are printed on the reverse side of the overlay. Thus, when viewed from the front, it is evener, more uniform and softer. After screen printing, graphic overlay manufacturers will seal them. Prevent the overlay including texts and graphic marks from external dirt, and keep it clear. The surface of the panel can withstand a variety of solvents and can be washed, so the decoration effect is good.
5.5 Economic benefit
Switch production is made at one time according to the final membrane switch design. The connection of the switch group and the lead-out of the switch circuit have been screen printed at one time by special printing methods. In terms of the cost of switch processing, the cost is lower than that of discrete parts especially for large-scale manufacture. In terms of the overall cost of the user, it also has these economic advantages.
Firstly, there is no need of punching and fixing, which greatly reduces the assembly process. Secondly, the connection of the switch group does not need to be welded one by one. It can not only save time but also avoid the hidden trouble caused by welding quality. Thirdly, there is no need to configure the panel, dig holes and open windows on the display part of machine interfaces. At the same time, due to the innovative structure and strong sense of the times, it can improve the credibility and market competitiveness of products. of course, the added value generated is still obvious.