PCB silk screen printing plate production process can be divided into two aspects
Pull net, net sun;
There are many small operations in these two areas. Let's take a look together.
1. Pull net
Steps to pull the net: Frame cleaning - horizontal inspection - coating the bottom layer - pulling the net - measuring tension - coating adhesive - under the net, edge - storage
Due to repeated use of the frame, there are residual adhesives, net yarns, and other debris around the frame, which must be removed to avoid affecting the adhesion of the mesh to the frame.
Place the frame on the platform (need to be level) to check whether the frame is deformed, and if it is deformed, it needs to be leveled
After cleaning, the undeformed net frame and the mesh yarn will be evenly coated and coated with a layer of Nan Bao Quan Zhi (without hardener) to enhance the adhesion of the mesh yarn to the frame after the net is pulled.
After about 10 minutes of gluing for the first time, place the net frame on the pull net and adjust the relative position and height.
Select the mesh, loosen around the mouthpiece, lay the mesh on the frame, and then evenly insert the mesh into the mouth of the mouthpiece. There should be no wrinkling. Note that there must be more loose mesh yarn in the corners, and the mouthpiece must be locked. Tight, there can be no gap between the clip and the clip (automatic lifting, manual pulling, for example)
Pull the net: the first tension 26, standing for 5 minutes tension is 24; second tension 28, standing for 5 minutes tension 26; third tension 32, standing for 5 minutes tension is 30; fourth correction 5 points Tension 32, sizing tension after standing for 20 minutes 30; 15 minutes under plastic curing under the net tension 28, after standing for 72 hours before the production of screen (a one meter × one meter automatic production line using screen version as an example).
The glue that has been adjusted is evenly brushed on the surface of the mesh frame and mesh yarn with a small brush, and the glue cannot be dropped into the middle portion of the screen plate. After the glue is dried for 8 minutes, the available blade plastic will not be completely stuck on the coating surface. The combined place is pressed tightly and the glue is thoroughly dried after about 10 minutes in the contract (open air blower should be used to strengthen and dry).
Remove excess net yarn around the screen, and indicate the tension on the screen border, date, mesh and under the net (so as to observe tension changes). In order to prevent infiltration of white water, seal with red glue in the inner corner of the frame, and then use The waterproof tape is sealed over the mesh frame and the mesh surface, preventing the infiltration of the liquid medicine.
2. Net sun
Wash the net: grind the net grease to the grease (new net), ghost paste to the graphics (the old net), in addition to the slurry to the net pulp, blue oil, use anti-white water to wash debris, rinse the net with detergent, and finally with high pressure The water gun is rinsed clean and finally cleaned with pure water.
Grilling network - oven set temperature should be less than 48 degrees Celsius.
Adhesive film: Clean the net and then wash it with purified water. According to the engineering film, increase the figure by 20%. Select the water film, use the triangle ruler to press the water film end on the net, then slowly use the triangle ruler to scrape upward, and then use a rubber scraper to gently press and wipe the excess water. Drying
The use of network pulp: drying stencil and then sizing, the use of scraping boxes, loaded net box scraped onto the net, which green oil three times, (about once every 10 minutes or more) bottom oil, surface oil is secondary, blue plastic first On the 50K film, tear off the film, and then on the screen 20 times, scrape three times each time (we have used automatic sizing machine), drying after the sizing is completed.
The selection of mesh yarn is generally line, green oil, base oil, surface oil with 120T, 100T, 110T mesh yarn, carbon oil 51T, blue plastic 24T photosensitive line and heat curing green oil with 77T
Film selection line uses 18K water film (without network pulp due to uneven use of network pulp will produce: dog teeth, fat oil, waves), green oil, base oil, surface oil selection of pulp, carbon oil use 50K water film
With the desired project graphics film attached to the position selected by the screen, placed on the exposure machine for light exposure, the choice of time (3000W spotlight), the line is generally 60-80 seconds, 80-100 seconds of green oil, the bottom character oil 40- 60 seconds, carbon oil, blue glue 350-400 seconds
Pressurized water net, dry.
Seal the outer edge of the graphic film with blue oil (sealing paste) and dry it.
Check, repair the net, write the completion date and each corresponding serial number and record it for archiving and storage.
Of course, this is only a general operation step. The ancients did not believe in books as good as books. If the actual operation is strictly in accordance with this method, it is extremely unwise. We should study and use it in order to make continuous progress and make better products. .
PCB silk screen specification
PCB silk screen printing technology has a lot of norms, not just can be done, these specifications prompted the development of PCB silk screen technology, let's take a look at the following specifications:
All components, mounting holes, positioning holes have corresponding silk screen labels. In order to facilitate the installation of the finished board, all components, mounting holes, positioning holes have a corresponding silk screen number, PCB mounting hole screen printing with H1, H2... ...Hn to identify.
The silkscreen characters follow the principle from left to right and from bottom to top. The silkscreen characters follow the principles from left to right and from bottom to top as much as possible. Electrolytic capacitors, diodes and other polar components are kept in the same direction within each functional unit. .
There is no screen printing on the pad of the device and on tin tracks that require antimony tin. The device position should not be blocked by the device after installation. (Excluding screen printing on higher density PCBs)
In order to ensure the reliability of the device's welding, there is no silk screen on the device pad; in order to ensure the tin channel continuity of tin-silicon, the tin channel of tin-negative tin is required to have no silk screen; in order to facilitate device insertion and maintenance, the device position number should not be After installation, the device is blocked; screen printing can not be pressed on the via hole and the pad, so as to avoid the loss of part of the silk screen when the resistance welding window is opened, which affects the training. Silk screen spacing is greater than 5mil.
The polarity of polar components is clearly shown on the silk screen, and the polar direction marks are easily identifiable.
The number of PCB photo files is correct, each layer should have the correct output, and a full number of layers output.
The device identifier on the PCB must be the same as the one in the BOM list.
Directional connectors indicate their orientation clearly on the screen.
There should be a bar code position mark on the PCB. When the surface space of the PCB board is allowed, a 42*6 bar code silk screen frame should be placed on the PCB. The position of the bar code should be considered for convenient scanning.
PCB board name, date, version number, etc. made of information board silk screen location should be clear. The PCB file should have the board name, date, version number, etc. printed on the board to be silk screened. The location is clear and eye-catching.
There must be complete information about the manufacturer and anti-static labels on the PCB.