Three Methods and Functions Commonly Used in PCB Plate Processing(2)

How to use the calculation sheet:

① Expose with the pre-estimated exposure time plus double the time, develop in a normal way, select the one with the best effect after developing, that is, one of the clearest image ranges. Then multiply the actual exposure time by the coefficient marked on the selected image, which is the optimal exposure time.

There are 5 coefficients on the calculation film, namely: 1.0, 0.7, 0.5, 0.33, 0.25, and each coefficient corresponds to a target shape and a dot.

②If the coefficient of 1.0 seems to be the best coefficient, then double the exposure time just now and re-make the plate exposure test.

③If the coefficient of 0.25 seems to be the best coefficient, reduce the exposure time by half and re-plate the exposure test.

④If several consecutive coefficients meet the requirement, use the coefficient with a smaller upper limit when drying the dot pattern, that is, the exposure time is shorter, and use a coefficient with a higher lower limit when drying generally thicker lines, that is, the exposure time is longer.

⑤If several consecutive coefficients are satisfied, select the best coefficient according to the type of screen plate to be made by comparing the clarity of the thinnest line or dot of the target.

In addition, the closeness of the film, the glass cleaning of the exposure machine, and the degree of vacuuming all have an important impact on the quality of the printing plate.

Development: Taking advantage of the water-soluble characteristics of photosensitive paste, the unexposed photosensitive paste is washed away with water. The development method has a great influence on the fine screen. Before developing, water must be sprayed to make the photosensitive paste absorb water and swell first, and let it stand for 1to 2 minutes, and then use a high-pressure water gun to develop back and forth in a fan shape until the image is completely clear.

Note: The high-pressure water washing can not be too close to the screen, generally 0.8″1m, otherwise the pressure is too high, the lines are prone to zigzag, and some dots are washed out in severe cases.

Drying: Dry the water on the screen, and the temperature should not be too high, otherwise the screen tension will change, generally 40 to 45 ℃.

Revision and inspection: Repair and inspect pinholes and some NPTH holes.

Final exposure: further improve the adhesion between the photosensitive paste and the mesh, and increase the service life.

Sealing screen: Fill the empty part of the screen with the sealing screen paste to avoid ink leakage during printing.

(2) Photosensitive Film Direct Plate Making Method

Technological process: stretched net – degreasing – moistening – filming – drying – reinforcement – exposure – developing – drying – revision – sealing net

Method:

The photosensitive film, commonly known as water film, is made of a transparent plastic film with a thickness of 0.1mm as the film base, and a layer of photosensitive emulsion with a certain thickness is coated on one side. The film is adsorbed to the screen by capillary action, and after drying, the plastic base is torn off for exposure and development, and finally the desired pattern is obtained.

Wetting: Wetting is used to promote the formation of a uniform water film on the surface of the screen, so that the photosensitive film can be transferred smoothly.

Film: According to the type of screen, paste the photosensitive film on the wet screen scraper surface, and use the scraper to scrape off the excess water after attaching.

Drying: Generally, it should be dried below 40℃. After drying, tear off the plastic base and let it dry for a few more minutes.

Reinforcement: If you need to increase the number of printing plates, you can apply a layer of photosensitive paste on the blade surface after the film is dried, and it needs to be dried after coating.

Other parts of the operation are consistent with the photosensitive pulp plate-making method.

2. Indirect Plate Processing Method

Method:

The method of indirect plate making is to first expose the indirect film, harden it with 1.2% H2O2 and then develop it with warm water. After drying, a strippable graphic negative is made. Squeeze to make the film stick to the wet screen, peel off the film base, and dry it with the wind to make the screen printing screen.

Process Flow:

1. Stretched net – degreasing – drying

2. Indirect film – exposure – hardening – development

1and2 – Fitting – Drying – Revision – Netting

3. Direct Plate Processing Method

Method:

The method of direct plate making is to first place the photosensitive film on the wrist film coated with the photosensitive material on the worktable with the photosensitive material facing up, lay the stretched wrist screen flat on the film base, and then put it in the screen frame. The photosensitive paste is applied by pressure with a soft scraper, and the plastic base is peeled off after being fully dried. The screen can be used for printing with the photosensitive film wrist screen attached. After developing and drying, the screen printing screen is made.

Process flow:

Stretched net – degreasing – drying – stripping film base – exposure – developing – drying – revision – sealing screen