1. Single membrane switch recognition
It consists of a certain elastic material (PET) and a conductive layer. When we use metal dome membrane. It can provide rigid support for membrane switches. This is a multi-layer planar non-self-locking button switch. It has an elastic insulating film with a conductive pattern (switch contact). Although this is not the same as switching capacitive touch. But, it also has spacer elements that maintain a certain
stroke. The graphic overlay is its most prominent feature. Moreover, the thin film switch can be a combination of one or more tactile switches.
1.1 Outstanding features of single membrane switch
Unlike traditional metal dome switch, It has good waterproof, dustproof, oil proof and anti-harmful gas erosion characteristics. Similarly, stable and reliable performance and high quality are some of the reasons why membrane switches are favored. We can wash the membrane panel, and the characters are not damaged. The richness of color is the reason why the membrane switch manufacturer can quickly promote the membrane switch. At the same time, the membrane switch can switch capacitive touch to the machine interface. This also led to the metal dome switch gradually withdrawing from the stage of history.
1.2 Application of single membrane switch
Membrane switch panels have widely used in intelligent measuring instruments and medical instruments. Even CNC machines and electronic scales can use membrane switches. Undoubtedly, membrane keypads can use in home appliances such as remote controls.
2. Components of a single membrane switch
2.1 Membrane panel
This is a process made of an elastic film. And the general elastic film is divided into PC, PET, HP. The typical membrane panel has a certain functional character index. And it can mark the button position. It is a decorative panel with a transparent display window.
The industrial controllers adjust the parameter values of the machine interface through the control systems. The finished product of the thin film switch has completed. We can make a membrane keyboard with a graphical interface and a touch screen.
2.2 Touch keypad membrane
It is composed of a membrane switch and a membrane panel. The touch keypad membrane includes a metal film, a touch screen, a metal dome, and a graphical interface. So, membrane keyboards are usually straightforward to operate.
2.3 Return line resistance (guide band resistance + contact resistance)
We can turn on the membrane switch contacts. Then, the turned-on contact connects the resistance between the two leads.
2.4 Button force
The operating force applied to the membrane switch when the contacts are turned on.
3. The classification and advantages of membrane switches
According to the difference in structure, combination and process of the membrane switch, and the end product used by different crowd. Generally switches include can divide into the following commonly used types.
3.1 Metal shrapnel type (pot piece)
Using shrapnel as the key contact surface, it has three distinct advantages:
1. The button feels good and the intensity is even.
2. You can hear a crisp sound during operation.
3. It can still be used normally under a high-temperature environment.
However, it also has an obvious drawback. When the lining has a bump or a curved arc that is too large. Even snap action,the shrapnel may be damaged. This can cause a short circuit or no rebound.
3.2 Hot pressing hand type (polyester button)
The button uses the typical membrane material to print the contact surface. This will form a rigid support. And the bump is formed to form a resilience.
Its advantage is that the button life reaches more than one million and feels good. But, its use in high-temperature environments may cause the button to feel to weaken. But it is undoubtedly the most used product in the daily life, as well as the most stock membrane switch.
3.3 Flat touch type (no feel)
The contact surface does not use any secondary process. It can achieve a button life of more than 1 million times. Moreover, its contact area is large and easy to operate. This is a high quality product. However, its shortcomings are also very obvious. Due to the lack of feeling, industrial controllers is easy to cause misuse.
3.4 EL backlight type
The conventional touch keypad membrane can embed an EL backlight. Even in low-light areas can use this membrane switch, regardless of the site environment. regardless of the site environment. But, due to the high cost, and the EL needs to equip with a driver, the power supply 110v. This makes practical applications not much.
3.5 Light guide plate type
The conventional film switch can embed a light guide plate. It can also use a membrane switch in places where there is insufficient light. And make the switch as a whole more enjoyable. And its biggest advantage is that its cost is lower than the EL. But, it has the greatest advantage of the EL backlight type. The biggest drawback of the light guide plate type is its high thickness. This is only suitable for the embedded fixing method. Otherwise, it will affect all viewing of the switch.
3.6 PCB type
The membrane switch panels circuit layer uses a PCB (hard circuit board). It has low on-resistance and high precision circuitry. This should be the ideal one for membrane switches. But, it cannot be bent. As a result, the actual use of the application, the use of the scene is very limited. This makes it impossible to use on a wide range.
3.7 FPC type
That is the membrane switch circuit layer uses FPC (Flexible Circuit Board). Compared with the PCB type, it has the advantages of low resistance and high precision of the circuit. At the same time, due to its flexible nature, it can be bent. This allows for a wide range of screen printing. This makes it better to meet the actual application. However, due to its high energy capability, the technical requirements are high. The cost of the investment is large, resulting in a higher cost.
4. Material for Membrane panel
A single membrane material is suitable for making a panel layer. According to its type, it can be generally divided into three types: PC, PVC, and PET. The sand surface and the smooth surface (transparent film) constitute the surface state.
The comprehensive index of physical and chemical properties of PC materials is better. The inks it adapts to are also more extensive. So, it has become the most common material for membrane switch panel applications. PC materials have the difference between sand and glossy. Because electronic products mostly used the tactile switches. So it chooses the sand surface material. Panels that operate as control systems are not expected to be subject to light interference. The sand-like surface is only reflective and does not produce bright reflections. At the same time, due to the disordered sand-like surface, it has the effect of shielding scratches. In contrast, glossy materials do not have the above characteristics.
As a glossy material, once printed on the back, the color will appear more vivid. In cases where the decorative requirements are strong and do not need to touch, usually, we choose a smooth panel. Or because of the special needs of some display areas such as LCD screens. It is helpful to use a smooth material.
4.1 Material comparison of Touch keypad membrane
The price of PVC film material is relatively low, about one-half of that of PC materials. If you produce popular civilian products. If you choose PVC materials, you can reduce production costs. At the same time, the PVC material has good elongation, and it can use cold pressing to process. Glossy PVC sheets generally have a thickness of more than 0.5 mm. Both sides use PET or glue paper as protect. Make decorative panels can use it. The PVC material of the sand surface is generally less than 0.3 mm thick. It generally supplies the fixed-length sheets without coils.
The surface state of the PET metal dome membrane is divided into a smooth surface and fine sand. It applies to products with high requirements for scratch protection. But the price is higher. PET film has a long life and good corrosion resistance. And its excellent insulation performance. So, the required instrumentation and home panels usually use it.
5. Technical requirements for single membrane switches
5.1 shape
Its graphic overlay, conductive lines, must follow the drawings. Moreover, the insulation treatment and the lining combination must also follow the drawings. Unless a physical sample can provide. In addition, industrial control is important to the shape of the membrane switch. Especially when performing large-scale screen printing, it is mechanized due to snap action. In the event of a mistake, the situation will be very serious. However, with the advent of mechanical pages, the difficulty of industrial control has been reduced. However, artificial industrial control is still very important.
5.2 Draw membrane panel drawings
Silver paste and carbon ink should follow the provisions of the drawings. Adhesives, adhesives, reinforcing plates, and insulation printing should also follow the drawings.
5.3 Appearance of single membrane switch
1. The surface of the metal dome switch must have no residual material or foreign matter. Even stains, bumps, and grease adhering to the surface and inside must not remain. Similarly, the fingerprint on the line, the burr of the shape have to clean.
2. The line must not have any foreign objects attached to it.
3. All lines and joints must not have cut through the table. Slight scratches are also based on the principle that the impedance is not affected. The surface of the carbon ink is easily scratched, and the scratches are not affected by the line conduction.
5.4 Line conductor of single membrane switch
1. The thickness of the conductor is generally controlled within 7-12 mm and should be uniform and smooth.
2. The conductor is not allowed to have any break or short circuit.
3. Carbon ink covering the silver paste line should ensure that the silver paste is completely covered. Its thickness is 8-10 mm, and there must be no obvious silver paste protruding.
5.5 Insulation printing
1. Do not have any insulating ink attached to all membrane switch contacts.
2. The surface of the insulating ink should be flat to avoid any defects, such as bubbles or pinholes.
3. Adhesion strength, after the insulating ink, is dried. The ink faces were placed against each other and then pressed for 24 hours. After that, make sure that the insulation is not sticky. Adhesive with a sub-sensitive tape to remove no air bubbles for 1 minute. Then we have to peel off quickly. At the same time, there is no ink falling off.
4. The line conductor requires all jumper sections. All jumper products are subject to 100% open, short circuit test, and insulation resistance test. Make sure that there are no public, short, and insulation resistances greater than 500 MA.
5.6 Electrical performance
1. In a normal temperature and humidity environment, the insulation resistance of the conductive line is greater than 500 MA. In the high temperature and constant temperature test, the salt spray test should be no less than 20 MA.
2. The return line resistance value is no more than 100 MA. The total length of the return, a line is greater than 150cm and special requirements. The return line resistance has additionally specified in the drawing.
5.7 Environmental testing
The stock membrane switch is subjected to high temperatures of around 55 degrees Celsius. After that, it took 72 hours of high-temperature action. After switch capacitive touch, the quality of the inspection should be under 4.13
