Screen printing method
From Figure 2-1, it can be seen that the screen printing method is only made of black and white films after making black and white films. The circuit to be printed on the screen is made like a mimeograph printed on a wax paper. After the screen plate is made, similarly to the stencil printing method, the copper to be retained on the copper-clad board is printed on the cleaned copper-clad board with a resist-printing material, followed by drying and etching. Here mainly introduces the screen version of the production.
There are many methods for producing silk screens, and self-made photo-resist films can be used, for example, dichromate sensitized adhesives can be made by adding dichromate aqueous solution with rubber, and can also be made into diazo sensitized glue by using aggravated nitrogen powder (100:1). It is also possible to purchase a photosensitive film that has already been prepared, and attach the photosensitive film directly to the screen to make a screen printing plate. The following describes the method of making a screen plate with a photosensitive film.
Screen printing method:
(1) Selection of screens
180-300 mesh nylon mesh (metal wire mesh can also be used). Then, use artificial or mechanical methods to stretch the screen, and use a diluted alkali solution or detergent to remove oil stains on the screen, and finally rinse with water and dry it for use on the photosensitive film.
(2) Prepare Photosensitive Film
According to the size of the black and white film, appropriately squeezing out the desired size of the photosensitive film, and gently wipe off the talcum powder on the photosensitive film with a silk cloth.
(3) Photosensitive film
Mix dichromic acid and water in an aqueous solution of ammonium dichromate in an amount of about 4% by weight, apply a layer of ammonium dichromate solution evenly on the screen, and then apply a screen film on the screen. There will be a polyester film surface attached to the screen), and then once again on the back of the screen brush ammonium dichromate solution, and finally with a hard rubber or plexiglass scraper first scrape the grease film surface to catch the bubble, and then the back of excess Scrape the solution. In this way, the photosensitive film is attached.
(4) Drying
Bake in a drying oven at about 45°C for 10-15 minutes. Peel off the polyester film after drying, and put it back in for 1-2 minutes.
(5) Exposure
The photographic film on the surface of the silk screen film smooth close to place, with 1000W high-pressure mercury lamp, the lamp is about 30cm away from the negative film, irradiation for 3-4 minutes, the UV sensitization. Can also be exposed to strong sunlight.
(6) Development
Place the exposed screen in warm water of about 40°C, and swing it gently for 1-2 minutes. After most of the graphics appear, rinse it with cold water until all the graphics appear.
(7) Dry
After development, place the screen in a well-ventilated place, air dry naturally, or dry at low temperatures.
(8) Trimming the screen plate
Where there is no need for missing prints, repair with a plugging paste. After repairing, seal with a plugging paste.
The above is the entire screen plate production process.
If self-made photosensitive adhesives are used to make screen printing plates, first clean the screen, then pour the prepared photosensitive adhesive on one end of the screen, and then use a Plexiglas scraper or a hard rubber scraper (the edge of the doctor blade must be straight and unnotched) evenly. Scratch the glue on the screen. In order to ensure that the film has a certain thickness, it can be coated on the screen for 3 to 5 times.
By making a good screen, you can make a printed circuit board. The printed material can be mixed with a certain color of lacquer by sifting the talc powder through the wire mesh, and transferred into a suitable concentration of the printing material, and then scraping the circuit onto the clean copper-clad plate with a scraper.
The screen plate is not used or the pattern is damaged. The omentum can be removed and the screen can be recovered for re-plate use.