1. Origin and classification of Membrane Switch
1. Origin:
1) The graphics are made on the film substrate, and the entire component is a Switch function, which is called the film switch, and the English name is Membrane Switches.
2). Several layers of films made of different materials are bonded to form a finished product with a thickness of about 1, 2 ~ 2, 5MM. The appearance is like a plate, and has the dual function of panel and switch, so it is also called panel switch, English name PANEL SWITCHES, or called a thin plate switch.
3) Due to the short travel range of this switch, it is only about 0.25 ~ 0.5MM, and the pressing force of the switch is 0.5 ~ 1N, which is more sensitive. The touch switch completes the function of the switch, so it is also called the touch switch or the touch Keyboard.
2. Classification:
1) According to the circuit substrate, it is divided into flexible board and rigid board
2) According to the shape of the panel, it can be divided into flat or three-dimensional
3). According to the operation experience, it can be divided into non-inductive and inductive
4). Divided into transparent type and finger touch Screen type according to special purpose
5). Divide the panel and discrete parts, keycap and keyboard according to the combination
6) Here we only discuss the use of sheets and printing materials for flexible board membrane switches (R).
2. Membrane switch structure form and currently commonly used R structure
1. Structure: flexible board (R) and rigid board (Y)
1), R structure: the panel layer, isolation layer and circuit layer of the membrane switch are all composed of soft films with different properties such as PET, PC and PVC.
2), Y structure: the pattern and circuit of the switch are made on both sides of the ordinary double-sided printed circuit double-coated copper board, and the two sides of the circuit are communicated through the metallized holes, and the components are welded on the back side, and the metal guide is used as the labyrinth The contacts of the disk and the wipers are wound with flat cable leads.
3. Membrane sheet used in membrane switch
Panel materials: AUTO TEX products co-operated with British and Sanhe International, with different thickness specifications (thickness 0.12 ~ 0.25UM) panel materials.
Sand surface PET: F series (fine sand surface), V series (coarse sand surface). It has a good polar sheet that can be convex and specially chemically treated on both sides. The transparent window liquid can be printed on the sand surface, and the PVC and PC inks can be printed on the glossy surface.
Hard coating chemically treated PET: EBG (glossy) series EBA (matte) series
Hard-coated PC tablets have different specifications: AUTOFLEXPC G (glossy) AUTOFLEXPC A (matte)
Sheets for circuit layer: available: AUTOTEX special PET.
After heat-stabilized, anti-shrinkage treatment and adhesion treatment, the glossy PET sheet has AUTOSTAT CT3, CT4, CT5, CT7, the thickness is 25, 100, 125UM.
The mist-shaped PET sheet after heat stabilization, anti-shrinkage treatment and adhesion treatment is HT5 and the thickness is 125UM.
The opaque white satin-like PET sheet after heat stabilization, anti-shrinkage treatment and adhesion treatment is WT5 and the thickness is 125UM.
Isolation layer usually uses 0.05 ~ 0.2MM thick PET, PVC, its thickness depends on the key position and the size and form of the isolation window. The isolation window is made by stamping.
4. Printing materials and printing
Window fluid: UV curing type. There are WINDOTEX GLOSS (glossy and transparent), WINDOTEX ANTIGIARE (matte) that is matte, FOTOTEX UV MATT (sand). Glossy transparent window liquid and matte window liquid can be mixed to achieve the desired effect. Stir thoroughly before printing, 100T silk screen, 25 # ~ 35 # capillary film to make screen, avoid sunlight printing, the printing sequence is placed in the first or second process of panel printing. The window liquid can restore the window of the matte surface to be transparent and can also make the transparent window an opaque matte surface.
The screen-printing glue can be selected from Sanha International Kamelia brand C / Tacr110. The glue is suitable for -40 ~ 180 ℃. The applicable materials are PET, PC, PS, PP, PMMA, metal and glass.
Panel layer decorative ink
A. The inks for panel use are solvent volatile inks. There are many types of inks in this respect. However, it should be considered from the aspects of ink fineness, pure hue, strong hiding power, and strong bonding with the substrate PET. It is recommended to choose the German Belong TJ series, Japan Seiko GAP series, Lisa GV and other series.
B. Panel printing is printed on the glossy surface of PET with reverse characters and reverse patterns (if PET does not use AUTOTDEX sheet, it should be polarized).
C. Operate according to the requirements of solvent volatile ink (such as the ink must be fully stirred before printing).
D. The color printing should be followed by the dark color before the light color. For the light color block printing, try to print it twice as much as possible to ensure its hiding ability, so that the color saturation of the ink is increased, and double ghosts are avoided when the color is overprinted.
E. Pay attention to prevent the change of the hue of the light-tone ink when printing the light color on the dark background. The light-color ink should be printed in the negative version of the negative as much as possible to reduce the influence of the dark ink on the hue of the light ink. The ink is thicker, but it must be dry to make the ink cover stronger.
F. Pay attention to the requirements of front and back printing, generally printed in white and silver, which is used to prevent the circuit pattern behind the board surface from being exposed, while not changing the hue of the color ink, and can set the ink color printed on the panel to be more vivid. Therefore, the printing ink on the back side needs to be strong in hiding, poorly selected, not enough for one printing, and can be printed twice to achieve the effect.
The function of silk screen back cover on the back of the panel: In order to prevent the abrasion of the ink layer on the panel and protect the color of the graphics.
A. Clean the ink layer on the back of the panel once to improve the covering ability and prevent the circuit behind the panel from being exposed.
B. The back cover ink must be silk-screened on the back of the panel. The back cover ink can use Baolong TJ-944 (white). It is best to use silver ink for silk screen printing.
Decoration of the transparent window part of the panel:
A. Printable Kotu Thai window fluid
B. Special color transparent ink can be printed. The color of the color transparent ink should be consistent with the color and wavelength of the light-emitting element of the light-emitting device to make the emitted light brighter.
C. How to choose and use the three primary colors with good transparency to make the transparent ink show high color transparency in the transparent window part. In practical applications, it is found that the transparency is not very good. Another kind of good transparency and wrinkles on the surface of the ink layer are very convenient for poor transparency. You should re-select fine inks, such as German Baolong, Seiko, and Liseda GV series Skin-like wrinkles should be considered from the pre-press treatment of the ink. Remove slight wrinkles on the ink surface.
The conductive printing material is silk-screened on the conductive layer. Generally, there are many silver inks and carbon inks on the film surface. The conductive inks commonly used on membrane switches are:
1. Silver ink: American Atchison ink is specially used for the conductive silver ED427SS and ED478SS of the membrane switch. Their resistance values are less than 0.1Ω / □ and 0.025Ω / □, respectively. Therefore, ED427SS can be mixed with ED423SS arbitrarily.
2. Carbon ink: ED4233SS and ED725A are used exclusively for membrane switches, and their square resistance values are <50Ω / □ and <0.017Ω / □ Conductive ink characteristics:
3. The requirements for pre- and post-press process operations of screen-printing silver and carbon ink:
A. The silver and carbon inks must be fully stirred before opening the can lid, and should be stirred up and down, otherwise it will appear in the same can of silver ink at different screen-printing stages. The resistance and conductivity of the imprint are different, and sometimes it can also affect Adhesion to the film.
B. After the correct screen-printing operation, the silver carbon ink must be stopped on the film for a while, so that the solvent wets the sheet and then placed in the oven, dried as required to ensure the adhesion to the film.
C. In order to accurately achieve the conductivity of screen-printing silver ink, it is generally dried in three stages after printing, that is, low temperature, medium temperature, specified temperature, and dry. If the resistance value deviates from the requirements, it needs to be dried again until the square resistance value reaches silver. Ink design requirements.
D. The resistance value should be measured according to the square resistance value Ω / □, because the line end resistance value does not take into account the width and thickness of the printed line, so the line resistance is not the standard resistance value of the original silver and carbon ink.
E. The silver ink that has not been printed on the screen this time cannot be returned to the original tank. It should be poured into a clean tank and used next time to ensure the service life of the silver ink in the original tank.
F. Screen printing silver and carbon ink. Due to their characteristics, softer squeegee, thick film layer, thick screen, large openings, and light edges should be selected during screen printing. The printing principle of light scraping ink and heavy reinking is implemented.
4. Selection of insulating ink and main technical indicators: As the insulating ink for the protection of the lead of the membrane switch, the insulating ink matching the conductive ink and the film sheet should be selected first, which is very helpful for their adhesion in membrane switches, Edison's ED-452SS UV photocurable ink is often used. The color is transparent blue or colorless, and its insulation is 2400VAC / MIL. The technical parameters of the insulating ink are:
A. Stir thoroughly before use
B. According to the required insulation performance, choose the mesh of 160-300 mesh,
C. The light curing energy is controlled at 300-600MI / CM2
D. The silk screen ED452SS needs UV curing after 3-5 minutes, which is beneficial to achieve a better-quality effect.
The above is just some explanations on the materials used in the production process of the membrane switch, screen printing technology and other main aspects. In fact, in the production of the membrane switch, for example, the problem of static elimination on the sheet and the color change of decorative ink will also be encountered. As well as the screen-printing site and screen-printing environment, purification problems, etc. will affect the quality of screen printing. Therefore, it is necessary to properly adjust and match the screen parameters in the whole process of screen printing, the selection of ink characteristics, the hardness of the rubber scrape, the control of the scraping angle, and the setting of the scraping speed. The five screen printing variables will definitely produce excellent Membrane switch products.
We are a Membrane Switches manufacturer engaged in Graphic Overlay, Membrane Panels, Soft Circuits, Silicone Rubber Keyboard, LED, LGF Silicone Rubber Keypad. All kinds of customization, welcome to come to consult.
