Pvc Cling Film,Cling Film Food,Cling Film Roll,Pvc Food Wrap Film DONGGUAN YEE HUP TRADING CO,.LTD , https://www.yeehupacks.com
As shown in FIG. 1 and FIG. 2, the structure of the membrane switch itself is very simple. It is a composite of the decorative panel, the upper and lower electrode films, and the isolation layer. The switch surface is planar. 
Fig. 1 Schematic diagram of membrane switch package 
Figure 2 Membrane switch structure
Membrane switches have the advantages of overall flatness, thin body shape, low mass, good dust resistance, and excellent water resistance, and are semi-closed structures. In addition, there is a large degree of freedom in the choice of panel design and color. Its scope of application is expanding into desktop computers, copiers, fax machines, toys, square computers, word processors and other fields.
Membrane switch production process is generally:
Electrode plate processing → making silk screen plate → screen printing silver paste → drying → screen printing carbon paste → drying → stamping → screen printing plate → assembly.
The following is a brief introduction of membrane switch materials and screen printing processes.
1. Substrate
There are several types of substrates that are suitable for making membrane switch panels:
(1) Polycarbonate film
Polycarbonate film has a wide range of operating temperatures (-135-135°C). When the temperature or humidity changes, the performance of this material does not change much. This ensures that the panel can withstand all kinds of harsh environments use.
(2) PVC film
Temperature performance is poor, especially in high temperature conditions, the softening temperature of 59 °C, the elasticity is not as good as polycarbonate film. However, it has a high elongation (130%) and because of its low price, it is suitable for use under normal conditions.
(3) polyester film
Both elasticity and temperature resistance are good, and the price is between the polycarbonate film and the polyvinyl chloride film. However, because the surface of the film is difficult to be processed into a matt type texture, it is mostly a transparent sheet, and at the same time, the surface of the polyester film can not obtain a satisfactory printing effect for most plastic inks, and a special special ink is generally used.
(4) Polyethylene film
Polyethylene film has good physical properties and chemical properties, and can resist a variety of chemicals, such as alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, esters, ketones and alcohol ethers. However, the price of polyethylene film is higher.
2. Screen printing process
(1) Production of Screen Printing Plates
1 Screen selection: Printed panels generally use 180-240 mesh screens. When the characters, keyframes, etc. of the printed panel have contour outline requirements, a screen with a slightly higher number of meshes should be selected, but not exceeding 300-500 mesh. As well.
Printed silver paste contacts, generally use 180-240 mesh screen. The conductive silver paste consists of metallic silver particles in a metal silver paste with good electrical conductivity. The size and shape of the metallic silver particles and the metallic silver solid content are not the same. Metal silver particles are the main factors that determine the resistance of the switch circuit. When the conductor circuit is printed, the micro-twist of the conductor silver should be managed to pass through the screen smoothly. Therefore, the mesh number of the selected wire mesh should not be too fine. Although the printed screen is straight and fine, it can be printed with a good-looking circuit pattern, but in the microscopic state, it is only a loose structure. The solid silver content of the metal silver particles is very small, which is due to the silver. Most of the particles failed to pass through the wire mesh. Such a pattern not only has a large resistance, but also affects the electrical conductivity and the service life of the circuit, and it cannot meet practical applications.
2 plate making method. Direct method, indirect method, straight method can be used. Printed panels are mostly made of legal plates; printed contacts and circuits can be indirect 3D photolithography. Exposure during plate making should be sufficient to reduce film loss and improve edge sharpness. The film thickness is thick and the printing ink layer is thick. The thick conductive ink layer is a prerequisite for improving conductivity and reducing resistance.
(2) Printing
1 panel screen printing. The panel screen printing is similar to the general plastic film screen printing, except that it is printed on the back of the panel, ie printed on the non-touch surface of the panel, to ensure that the graphic on the membrane switch panel is permanently clear and free of wear. A wide variety of plastic inks, but with different properties. The ink drying schedule is about 0.5 hours dry, and it takes more than 5 hours to dry. Since the membrane switch panel undergoes multi-color printing, it is necessary to pay attention to the interval time for printing each color ink. To ensure the printability of the ink, the printing process is preferably performed under constant temperature and humidity conditions.
In printing color sequence, the principle of first dark color and light color should be followed. For large-area panel colors or color patches, especially light-colored patches are preferred to be printed twice, so that the ink layer is thickened, the ink is full, and the ink hiding power is improved. But to avoid overlapping colors, shadows appear.
After all the overprinting, it is also necessary to print a back color on the panel except the transparent window hole, which is usually called the bottom layer. The bottom layer has the function of preventing the ink layer from being worn, protecting the picture and text of the panel, and the color, and at the same time, the ink on the back side is also completely cleaned and the hiding power is improved to prevent the circuit on the back of the panel from being exposed. The ink used for sealing the bottom layer is preferably a silver ink. On the one hand, it has the characteristics of strong hiding power. On the other hand, it does not change the hue of the ink, and can set off the front ink more vividly.
Transparent windows on the panel In order to enhance the indication or display effect and mask the outline of the elements behind the transparent window, transparent colors are usually printed. The printed transparent window requires the use of a special transparent ink. The color of the window should be the same as the color of the light emitting element. This can improve the clarity of the light emitting element due to the wavelength matching. Printed transparent windows should use thin screens and thinner plates, and use harder squeegees to make the ink layers thin and even.
In addition, the membrane switch panel must be repeatedly overprinted, and also needs to be assembled with the circuit and the isolation layer as a whole. Therefore, the setting criteria of the panel is particularly important. In the printing of panels should pay full attention to the unification of the overprint reference, and the selection of this reference should pay particular attention to the design of the processing plan with the process reference, measurement datum, assembly register exactly the same, in order to ensure the accuracy of the membrane switch.
2 switch circuit screen printing. Printed switch circuit printed material is the most commonly used silver paste, because it is a viscous paste, it is also known as silver paste. Although it has been a long time to process electronic components by means of screen printing using silver paste, most of them belong to the high-temperature sintering reduction type. The silver paste used in the membrane switch circuit is limited by the temperature resistance of the substrate, and a low-temperature curable silver paste must be used. The silver paste for printing thin film switch circuits is currently of many types, and the performance and quality are also very different. The performance of silver paste should be evaluated from the aspects of resistivity, solid content, particle size of metal particles, bonding strength and curing temperature, and then selected. Since the silver paste is expensive and its quality is related to the conductive properties of the membrane switch, it should be carefully selected.
When scraping, you should follow the principle of returning to scratch. This squeegee method is used because the viscosity of silver paste is thicker than ordinary inks, and it also contains metal solid components. The so-called re-wiping, that is when the ink back to the silver paste has a certain degree of squeeze force, forcing it to fill the ink on the printing plate parts; light scraping is actually the process of cleaning the silver paste on the Internet and cut off the printing material, The fullness of the graphic has been determined by "return", and excessive printing force will deform the graphic.
3. dry
The presence of various solvents and additives in the conductive silver paste has a certain influence on the resistivity. To release them from the conductive circuit, they mainly rely on hot air drying to volatilize them. The drying temperature is generally controlled at 85-90°C, and it is heated for 40 minutes under hot air. It has been proved that dry conductive patterns are often 10 times higher than the dry pattern resistance.
Membrane Switch A switch made of a contact circuit printed on a flexible polycarbonate or polyester film with a conductive paste. It is a type of contact switch.