PCB Blog - Several steps of PCB board screen printing

1. Description:

1)Due to the repeated use of the PCB board mesh frame, there are residual viscose, mesh, and other debris around the mesh frame, which must be removed to avoid affecting the adhesion between the mesh and the mesh frame.

2)Place the screen frame on the platform (it needs to be level) to check whether the screen frame is deformed. If there is any deformation, it needs to be leveled.

3)After cleaning, the non-deformed mesh frame and the mesh are evenly coated with a layer of glue without hardener in order to enhance the adhesion between the mesh and the mesh frame after drawing the mesh

4)After about 10 minutes of gluing, place the screen frame on the drawing table, and adjust the relative position and height

5)Select the mesh, loosen the clamping nozzles around, spread the mesh on the frame, and then evenly clamp the mesh into the clamp, without wrinkling, pay attention to the loose mesh at the four corners, and the clamping nozzle must be Tighten, and there should be no gap between the clip and the clip (automatic lifting frame, manual pulling net as an example).

6) Stretching the net: the second tension is 26, and the tension is 24 for 5 minutes; the second tension is 28, and the tension is 26 for 5 minutes; the third tension is 32, and the tension is 30 for 5 minutes; the fourth correction is 5 points Tension 32, after standing for 20 minutes, the gluing tension is 30; after 15 minutes of glue curing, the lower mesh tension is 28, and the screen can be made after standing for 72 hours (take the screen plate used in a one-meter × one-meter automatic production line as an example). Synchronously pull apart longitudinally and laterally, and apply glue when pulling to the required tension. The common mesh tension is (100T, 110T, 120T are all 30±2 Newtons) (77T, 51T are all 35±2 Newtons) (24T is 35±2 Newtons) 50±2N)

7)Use a small brush to brush the adjusted glue evenly on the top of the screen frame and the mesh surface. Do not drop the glue into the middle of the screen. After the glue is dry for 8 minutes, you can use scraper glue on the glued surface. The place where it is completely fitted should be pressed for about 10 minutes after the glue is completely dried (the open-air blower should be used to strengthen drying) before the net can be removed.

8)Use a paper cutter to remove the excess mesh around the screen, and indicate on the screen frame, date, mesh, and tension when unloading (in order to observe the change of tension). In order to prevent the infiltration of washing water (anti-white water), The inner corner of the screen frame is sealed with red glue and then sealed with waterproof tape above the joint surface of the screen frame and the mesh to prevent the penetration of the potion.

2. The net

1)Washing the net: remove grease (new net) with grinding net cream, remove graphics with ghost cream (old net), remove net pulp and blue oil with desizing powder, wash sundries with anti-white water, rinse net with detergent, use Rinse with high-pressure water gun and clean with pure water.

2)Drying: -- The oven setting temperature should be less than 48 degrees Celsius.

3)Use the premium film method: wash the net with pure water. Select the water film according to the size of the engineering film patch by about 20%, press one end of the water film with a triangle ruler on the net, then slowly scrape it up with a triangle ruler, and then gently press it with a rubber scraper, and wipe the excess water with a towel. dry.

4)Use photosensitive glue (net pulp): dry the screen plate and then apply photosensitive glue, use a scraper box to scrape the net, in which the screen printing green oil needs to be sized three times, (about every 10 minutes or more) screen printing other anti-corrosion inks Then for the second time, the screen printing peelable glue (blue glue) is first applied with 50 micron water film to tear off the film, and then the mesh pulp is applied twice, scraping three times each time, and drying after the sizing is completed.

5)Selection of mesh yarn The general line includes silk screen printing of character ink, and 120T, 100T, and 110T mesh yarn for anti-corrosion ink (green oil, base oil, top oil), carbon paste (carbon oil) 51T, and screen printing peelable ink (Blue Glue) 24T screen printing photosensitive circuit and 77T for heat curing ink.

6)18K water film is used for the selection line of the film (use photosensitive glue without photosensitive glue to surf the Internet is easy to cause unevenness: such as burrs (dog teeth), etc.), other resist inks (green oil, base oil, top oil) choose photosensitive Glue (net pulp), carbon paste (carbon oil) use 50-micron water film

7)Paste the required engineering graphic film on the selected position of the screen, and place it on the exposure machine for exposure. The time is selected (3000W spotlight), the line is generally 60-80 seconds, the green oil is 80-100 seconds, and the bottom surface is character oil. 40-60 seconds, carbon oil, blue gum 350-400 seconds

8)Rinse the net with pressurized water and dry.

9)After the screen is made, use sealing glue (blue oil) to cover the areas on the screen that are not covered by film or photosensitive glue, scrape the sealing glue with a screen scraper, and dry.

10)Check, repair the net, write the completion date and the corresponding number, and record, archive, and store.

3. Storage

When stored, it is generally stored vertically. The mesh frame can be made or purchased. It needs to be stored in the same environment as the screen printing environment to prevent deformation. At the same time, the tension of the screen needs to be tested before the screen printing, and the graphics can be checked with photographic negatives on the PCB board.