Three kinds of screen printing plate making method comparative analysis

Screen making category

Platemaking methods Materials used Direct platemaking Photosensitive film Photosensitive film Direct and indirect plate method Photosensitive film Indirect plate making method Indirect film

1. Direct plate making method

(1) Photosensitive pulp direct platemaking method: Apply a certain thickness of photosensitive paste (usually a diazonium salt photosensitive paste) on a stretched screen plate, apply it and dry it, and then attach it to a plate making machine with a plate making film. Exposure, developed, rinsed, and dried becomes a screen-printed screen.
Process flow: Photosensitive paste preparation stretched - Degreasing - Drying - Coating - Drying - Exposure - Development - Drying - Revision - Final exposure - Closure

The method and role of the various sections of the degreasing: The use of degreaser to remove the grease on the screen so that the photosensitive paste and the screen are completely glued together is not easy to film.
Drying: Drying moisture, to avoid tension due to the high temperature of the mesh, the temperature should be controlled at 40 ~ 45 °C.
Photosensitive paste preparation: The photosensitizer with pure water and mix well after adding the photosensitive paste, stir, put 8 hours later use.
Coating film: The photosensitive paste is evenly coated on the screen by means of a scraping groove, and is divided into an automatic coating machine coating and a manual coating according to a coating film method, and the coating film number may be determined according to actual conditions.

The first step is to coat the blade surface with the purpose of first filling the gap between the meshes to avoid air bubbles, and then coating the printed surface (the side that is in contact with the PCB). The current automatic coating machine is used for each coating. The film thickness can be increased by about 3 μm at a time. Therefore, most of the screen coating methods for the solder mask are selected as follows: coating on the blade surface twice—drying—printing surface coating three times—drying—printing surface coating three times—drying—printing surface Coating three times - drying coating method is correct:

A. The correct coating The thickness of the blade surface and the printing surface is appropriate and meets the requirements
B. Thin film (printing surface) Disadvantages: poor durability
C. Scrape face film is too thick Disadvantages: Due to the blade surface of the photosensitive paste is too thick, so that uneven photosensitivity, development water rinse, the surface of the rough ink poured into the film, the film off, leading to shortened screen life.
D. Scrape face film is too thin Disadvantages: poor durability

Drying: The photosensitive paste is dried evenly to prevent the photosensitive paste from being wet inside. The high temperature will allow the outer photosensitive paste to dry first and the inside of the paste will not dry. The screen life will be shortened and the temperature should be maintained at 40-45°C. About 10 minutes, adjust the drying time according to the different film thickness.

Exposure: Appropriate exposure allows photopolymerization of the photopolymer to develop a clear image through the master plate.

Factors affecting the quality of the screen :

A. The correct exposure energy
B. Exposure and vacuum
C. Exposure Glass Cleaning

The general exposure energy is adjusted with the exposure time. During the production, the correct exposure time of each type of screen should be determined by using the exposure measurement sheet according to the screen number and film thickness.

Measurement sheet use method:

1Exposure by pre-estimating the exposure time and doubling the time. Develop in the normal way. After development, select the best one, which is one of the sharpest image ranges, multiplied by the actual exposure time. The coefficient on the image is the better exposure time.

There are 5 coefficients on the measurement sheet, namely: 1.0 0.7 0.5 0.33 0.25 Each coefficient corresponds to a circle target pattern and a dot

2 If the coefficient of 1.0 seems to be the best factor, it should be doubled with the exposure time just before, and the plate-making exposure test should be repeated.

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

4 If several consecutive coefficients are satisfied, the lower limit coefficient is used when printing the dot pattern, that is, the exposure time is shorter, and the lower limit factor is higher when the sun is generally thicker, ie the exposure time is longer.

5 If several consecutive coefficients are satisfied, select the best factor for comparing the sharpness of the thinnest line or dot of the circular target according to the type of screen printing.

In addition, the closeness of the film, the glass of the exposure machine, and the degree of vacuum have an important influence on the quality of the printing.

Development: The use of water-soluble characteristics of the photosensitive paste, using water to wash away the unexposed photosensitive paste, the development of the way has a great impact on the fine screen, must be developed before the water to make the photosensitive slurry first soaked up, standing 1 ~ In 2 minutes, it is fanned back and forth with a high pressure water gun until the image is completely clear.

Note: High-pressure water washing can not be too close to the screen, generally 0.8~1m, otherwise the pressure is too high to make the lines easy to generate sawtooth, and some of the dots are washed out in severe cases.

Drying: Dry the moisture on the screen, the temperature can not be too high, otherwise it will produce screen tension changes, generally 40 ~ 45 °C

Revision, inspection: Repair and inspect the pinhole and some NPTH holes.

Final exposure: Further increase the adhesion of the photosensitive paste and mesh yarn and increase the service life.

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

(2) Photosensitive film direct plate making method

Process flow: stretched net --- degreasing --- moist --- film --- drying --- reinforcement ---exposure --- development ----drying --- revision --- closure net

method

The photosensitive film, commonly known as shuifeilin, is a transparent plastic film with a thickness of 0.1mm. It is made by coating a layer of emulsion with a certain thickness on one side. When used, the screen is fully wetted and then the film is applied. The film is adsorbed onto the screen by capillary action. After drying, the plastic film is peeled off for exposure and development. The desired pattern is finally obtained.

Wet: The use of moisture promotes the formation of a uniform water film on the surface of the screen, so that the photosensitive film can be smoothly transferred.
Film: According to the type of screen, the photosensitive film is attached to the surface of the wet screen blade, and then the excess water is scraped off with a scraper.
Drying: Drying is generally performed at a temperature below 40°C. After drying, the plastic substrate is torn off and dried for a few minutes. If it is necessary to increase the number of printing plates, a layer of photosensitive paste may be applied to the surface of the blade after drying. Dry after coating.

Other parts of the operation are consistent with the photolithography process.

2, direct and indirect plate making

method

The method of direct and indirect plate making is to place the photosensitive film coated with a photosensitive material on a worktable surface with the photosensitive film facing upwards first, and lay the flattened wrist frame on the film base and then put it in the frame. The photosensitive pulp is coated with a soft scraper, and after drying, the plastic film base is peeled off, and a photosensitive film wrist net is attached for use in printing. After developing and drying, a screen printing screen is produced.

Process flow:

Extruded - Degreasing - Drying - Peel off film - Exposure - Development - Drying - Repair - Closure

3, indirect plate making

method

The method of indirect plate making is to expose the indirect film firstly, harden it with 1.2% H2O2, develop it with warm water, and dry it to make a peelable graphic negative film. When making the plate, stick the film surface of the graphic negative film to the stretched silk screen. Extrusion to glue film and moist silk screen, peel off the film base, and blow dry to make screen printing screen.

Process flow:

1. Stretched - Degreasing - Drying

2. Indirect Film - Exposure - Hardening - Development

1and2 - Fit - Dry - Repair - Closure

Reprinted from: Chen Yi