Silk screen printing process in the manufacturing

In the film switch manufacturing technology, the silk screen printing process

I. The Origin and classification of the film switch:

1, origin:

1). The graphics are made on the film substrate, and the whole component is a switching function, so it is called the film switch, which is called the membrane switch in English

2). The finished product is glued by several layers of films of different materials, with a thickness of about 1, 2~2, 5mm. Its appearance is like a plate, and it has the dual functions of a panel and a switch. Therefore, it is also called a panel switch. Its English name is panel switches, or a sheet switch

3). Because the action stroke of this kind of switch is short, only about 0.25~0.5mm, and the pressing pressure of the switch is 0.5~1n, it is sensitive, and the switching effect can be completed by touching it gently, so it is also called touch switch, or touch the keyboard gently

2. Classification:

1), divided into flexible board and rigid board according to the circuit base material

2), divided into planar or three-dimensional type according to the panel shape

1, the relationship between foaming and bridging 3), divided into non sensory type and sensitive type according to the operation feeling

4), divided into transparent type and finger film screen type according to the special purpose

5), divided into panels and discrete parts and keycaps and keyboards according to the combination mode

6) Here we only discuss the use of sheet and printing material of flexible plate membrane switch (R)

II. Structural form of membrane switch and currently commonly used r structure

1. Structure: flexible board (R) and hard board (y)

1). R structure: the panel layer, isolation layer and circuit layer of membrane switch are all composed of various soft films with different properties, such as pet, PC and PVC

2). Y structure: the graphics and circuits of the switch are made on both sides of the copper clad plate of the ordinary double-sided printed circuit respectively. The circuits on both sides are communicated through the metallized holes, and the components are welded on the back side. The metal guide is used as the contact for conducting the labyrinth contact plate, and the friction part is wound with flat cable leads

3. Thin film sheet used in membrane switch

panel material: Auto tex products cooperated by British cotutay and Sanhe international have different thickness specifications, including (thickness 0.12~0.25um) panel material

sand surface pet includes: F series (fine sand surface), V series (coarse sand surface). It has a good polarity sheet that can be convex, and both sides have been specially chemically treated. The sand surface can be printed with transparent window liquid, and the smooth surface can be printed with PVC and PC inks

hard coated chemically treated PET: EBG (smooth surface) series EBA (fog surface) series

hard coated PC chips have different specifications: autolexpc g (smooth surface) autolexpc a (fog surface)

sheet for circuit layer: there are: special pet for autotex products

glossy pet sheets after heat stabilization, anti shrinkage treatment and adhesion treatment include autostat CT3, cT4, CT5 and CT7, with a thickness of 25100125um respectively

the foggy PET sheet after heat stabilization, anti shrinkage treatment and adhesion treatment is HT5 and the thickness is 125um

the opaque white satin PET sheet after heat stabilization, anti shrinkage treatment and adhesion treatment is WT5, and the thickness is 125um

the isolation layer usually uses pet and PVC with a thickness of 0.05~0.2mm, and its thickness depends on the size and form of the key position and the isolation window hole. The separation window hole is made of stamping

4. Printing material and its printing

window solution: UV curing type. There are windowstex gloss (smooth and transparent), windowstex Angel (fog surface), i.e. matte surface, and fototex UV Matt (sand surface). Smooth transparent window liquid and foggy window liquid can be mixed to achieve the desired effect. Stir thoroughly before printing, make plates with 100t silk, 25 #~35 # capillary film, print away from too much sunlight, and place the printing sequence in the first or second process of surface printing. The window liquid can make the window of the rough surface layout transparent, and can also make the transparent window become an opaque matte surface

printing glue can be selected from Sanhe international kemailai brand c/tacr110. This glue is suitable for -40~180 ℃, and is suitable for pet, PC, PS, PP, PMMA, metal and glass

decorative ink for panel layer

a. the ink for panel is solvent volatile ink. There are many kinds of inks in this regard, but we should consider from the aspects of ink fineness, pure hue, strong hiding power, strong combination with substrate pet, advanced production technology and leading output of a variety of polyurethane raw materials in China. It is recommended to choose German Baolong t-J series, Japanese Seiko gap series, reseda GV series, etc

b. Panel printing is printed on the smooth surface of pet with reverse words and reverse patterns (if pet does not use autotdex sheet, it should be polarized)

c, operate according to the requirements of solvent volatile ink (for example, prepress ink needs to be fully stirred)

d. for chromatic printing, it should follow the principle of dark color first and then light color. For light color block printing, it should be printed twice as much as possible to ensure its concealment, so as to improve the ink saturation and avoid ghosting in color overprint

e. pay attention to prevent the light tone ink hue from changing when overprinting light colors on a dark background. The light color ink should be printed with Yin text blank printing as far as possible to reduce the impact of deep ink on the light ink hue. If the blank printing method cannot be used, the Yang text ink printing should be thicker, but it must be dry enough to enhance the ink cover

f. pay attention to the requirements of the back color of the front and back printing. Generally, white and silver printing are used to prevent the circuit graphics behind the board from being exposed. At the same time, the hue of the color ink is not changed, and the ink color printed first on the panel can be set off more brightly. Therefore, the back printing ink requires strong covering, poor selection, insufficient printing once, and can be printed twice to achieve the effect

the function of the silk screen back cover on the back of the panel: to prevent the wear of the ink layer of the panel and protect the color of pictures and texts

a. clean the ink layer on the back of the panel once to improve the covering ability and prevent the circuit behind the surface plate from being exposed

b. The back cover ink must be silk printed on the back of the panel. The back cover ink can be Baolong t-j-944 (white). It is best to silk print silver ink, which not only covers the ink, but also makes the ink color more bright

decoration of transparent window part of the panel:

a, printable cotutay window liquid

b, printable special color transparent ink, the color of which should be consistent with the color and wavelength of light-emitting elements of light-emitting devices, so as to make the light emitted brighter

c. How to select and use the three primary colors with good transparency to make the transparent ink show high color transparency in the transparent window. In practical application, it is found that the transparency is not very good. Another kind of ink with good transparency and wrinkles on the surface of the ink layer is very convenient for poor transparency, so we should re select excellent inks, such as Germany Baolong, Japan as a new energy-saving, environmental protection, recycling, low-carbon material benseiko, and liseda GV series. For orange peel like wrinkles on the ink surface, we should consider the pre press treatment of the ink. Eliminate slight wrinkles on the ink surface

conductive printing materials are silk printed on the conductive layer. Generally, there are more silver ink and carbon ink on the surface of the film. Conductive inks commonly used on film switches are:

1. Silver ink: American Acheson ink is specially used for conductive silver ed427ss and ed478ss of film switches, and their resistance values are less than 0.1 Ω/□ and 0.025 Ω/□, respectively. In order to prevent silver discoloration and improve the wear resistance of the printing layer, ed427ss can be mixed with ed423ss at will

2. Carbon ink: ed4233ss and ed725a are specially used on the film switch, and their square resistance values are ＜ 50 Ω/□ and ＜ 0.017 Ω/□ respectively. Conductive ink characteristics:

3. Prepress and Postpress process operation requirements of silver and carbon ink for silk screen printing:

a. Silver and carbon ink prepress require full mixing after opening the can cover, and must be stirred up and down, otherwise the same can of silver ink appears in different silk screen printing stages, The resistance and conductivity of the imprint are different, and sometimes the adhesion with the film can also be affected

b. after the correct screen printing operation, the silver carbon ink must stop on the film for a moment, and then put it into the oven after the solvent moistens the sheet, and dry it as required to ensure its adhesion to the film

c. in order to accurately achieve the conductivity of silk screen silver ink, it is generally dried in three levels after printing, namely, low temperature, medium temperature, the specified temperature, and it should be dried thoroughly. If the resistance value deviates from the requirements, it needs to be dried again until the square resistance value meets the silver ink design requirements

d, the resistance value should be checked according to the square resistance value Ω/□ because the line end resistance value does not take into account the width and thickness of the printing line, so the line resistance is not the standard resistance value of this silver and carbon ink

e. the silver ink on the plate that has not been printed this time cannot be returned to the original tank. It should be poured into the clean tank and used first next time to ensure the service life of the silver ink in the original tank

f, silver and carbon ink for silk screen printing. Due to their characteristics, soft rubber scraper, thick film layer, thick wire, large opening and smooth edge should be selected during silk screen printing. Implement the printing principle of light scraping and heavy re inking

4. Selection and main technical indicators of insulating ink: as the insulating ink for lead wire protection of film switch, the insulating ink matching with conductive ink and film sheet should be selected first, which is very helpful for their adhesion. In film switching, Acheson's ed-452ss UV curing ink is often used, with transparent blue or colorless color, and its insulation is 2400vac/mil. The technical parameters of the insulating ink are:

a, fully stir before use

b, select the mesh of wire according to the required insulation performance,

c, control the light curing energy at mi/cm2

d, and UV curing after minutes of screen printing ed452ss, which is conducive to achieving better quality effect

the above is just a description of the materials used in the manufacturing process of the film switch, the silk printing technology and other main aspects. In fact, in the production of the film switch, there will be problems such as the elimination of static electricity on the sheet, the color change of decorative ink, the silk printing place and the silk printing environment, and the purification problems, which will affect the quality of silk printing. Therefore, we must correctly adjust and match the five silk screen variables, such as the selection of plate parameters, the selection of ink characteristics, the hardness of the squeegee, the control of the squeegee angle and the setting of the squeegee speed, which can also reduce the purchase cost by about 40%. Excellent film switching products will be produced