Three kinds of screen printing plate making method comparative analysis

Screen Making Classification Plate Making Method Using Materials

Direct plate method Photosensitive film

Indirect plate making method Photosensitive film

Indirect plate making method Indirect film

1. Direct plate making method

(1) Photosensitive paste direct plate making method

Method: A certain thickness of photosensitive paste (usually a diazonium salt photosensitive paste) is coated on a stretched screen plate, dried after coating, and then placed in a printing machine with a plate-making film and exposed, followed by development and rinsing. After drying, it becomes a screen printing screen.

Process flow: Photosensitive paste has been stretched - Degreasing - Drying - Coating - Drying - Exposure - Development - Drying - Revision - Final Exposure - Closure

The method and function of each section

Degreasing: The use of degreasing agent to remove the grease on the screen makes it impossible for the film to be completely glued together with the screen.

Drying: Dry the moisture to prevent the tension of the mesh from changing due to the high temperature. The temperature should be controlled at 40-45°C.

Photosensitive paste preparation: The photosensitizer is mixed with purified water and added to the photo-sensitive paste. Stir it well and let it stand for 8 hours before use.

Coating film: The photosensitive paste is evenly coated on the screen by means of a scraper, and is divided into an automatic coating machine coating and a manual coating according to the coating method, and the number of coating films may be determined according to actual conditions.

When coating the film, the surface of the blade should be coated first. The purpose is to fill up the space between the meshes first to avoid air bubbles, and then the printed surface (the side that comes in contact with the PCB) is coated. The current automatic coating machine is used for each coating. The thickness of the film can be increased by about 3 μm at a time. Therefore, most of the methods for applying the solder mask are the following: coating the surface of the blade twice - drying - coating the surface three times - drying - printing the surface three times - Drying - printing surface coating three times - drying.

The coating method is wrong:

A. The correct coating blade surface and printing surface thickness are suitable and meet the requirements.

B. Thin coating (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, water developed after the development, the surface roughness of the ink poured into the film, the film off, leading to shortened screen life.

D. Too thin coating on the blade surface Disadvantages: poor durability.

Drying: The photosensitive paste is dried evenly to prevent the photosensitive paste from being wet inside. The temperature is too high to allow the external photosensitive paste to dry before the inside is dry, and the screen life is shortened. The temperature should be kept at 40~45°C. About 10 minutes, the drying time is adjusted according to the film thickness.

Exposure: Appropriate exposure allows photopolymerized photopolymerization to develop clear images 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 various types of screens should be determined by using the exposure measurement sheet according to the screen number and the film thickness using the stepwise exposure method.

Measurement sheet use method:

1 Expose the exposure with a pre-estimated exposure time, doubling the time, develop the image in the normal way, and select the one with the best effect, ie, the sharpest image range, multiplied by the actual exposure time. The index coefficient on the image is the better exposure time.

There are five coefficients on the measurement piece, namely: 1.0, 0.7, 0.5, 0.33, and 0.25. Each coefficient corresponds to a circle target figure and a dot.

2 If the coefficient 1.0 seems to be the best factor, it should be doubled with the just-exposure time to re-plate exposure test.

3 If the coefficient of 0.25 seems to be the best factor, then the exposure time should be reduced by half and the plate exposure test should be repeated.

4 If several consecutive coefficients are satisfied, the lower limit coefficient is used when printing the dots on the screen, that is, the exposure time is shorter, and the lower limit factor is higher when the sun is generally thicker, that is, 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 circle target according to the type of the screen to be printed.

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

Development: The use of water-soluble photosensitive paste, the use of water to wash out 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, use the high pressure water gun to fan back and forth 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 large to make the lines easy to produce sawtooth, in some cases, some outlets are washed away.

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 part of the NPTH hole.

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 plugging paste to avoid ink leakage during printing.

(2) Photosensitive film direct plate making method

Process flow: already stretched - degreasing - wet - film - drying - reinforcement - exposure - development - drying - revision - closure network

method

Photosensitive film commonly known as water film, is a transparent plastic film thickness of 0.1mm for the film base, coated with a layer of a certain thickness of emulsion on one side, when used, first fully wet the screen, and then paste the film The film and the film are adsorbed on the wire mesh by capillary action, dried, and the plastic film base is peeled off for exposure and development, finally obtaining the desired pattern.

Wetting: 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 transferred smoothly.

Film: According to the type of screen, the photosensitive film is affixed to the surface of the wet screen blade, and the excess water is scraped off with a squeegee.

Drying: Generally, it should be dried below 40°C. After drying, remove the plastic film base and allow it to 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 to the surface of the blade after the film has dried. Dry it after coating.

The other part of the operation is consistent with the photolithography method.

2, direct and indirect plate making

method

The method of direct and indirect plate making is to first lay the photosensitive film coated with a photosensitive material on the worktable surface face up, and put the frame of the wrist frame flat on the film base, and then put it in the frame. The photosensitive paste is coated with a soft squeegee under pressure, and after being sufficiently dried, the plastic film base is peeled off, and the sensitized film wrist stencil is attached to the stencil, and after the development and drying, a screen printing screen is produced.

Process flow:

Has been stretched - degreasing - drying - peeling film - exposure - development - drying - revision - closure

3, indirect plate making

method

Indirect platemaking method is to indirect film is first exposure, with 1.2% H2O2 hardened with warm water after drying to make a peelable graphic film, plate the film when the film surface with a tight mesh stick tight, through The film was pressed to adhere to the wet screen, the film base was peeled off, and the silk screen plate was made by blow drying.

Process flow:

1. Stretched - Degreasing - Drying

2. Indirect film - exposure - hardening - development

1and2 - Fitting - Blow Drying - Revision - Closure