Film

writer: G May 23, 2019

1. Film rinse.

The film can be rinsed after exposure. Different negatives have different rinsing conditions. Before use, carefully read the instructions for the negative to determine the correct development and fixer formulation. The rinsing process of the film is as follows:

1> Exposure imaging: After the film is exposed, the silver salt is reduced to the center of the silver, but at this time, no pattern is visible on the film, which is called a latent image.

2> Development: The silver salt after the light is reduced to black silver particles.

3> Fixing: The silver salt that has not been reduced to silver on the film is dissolved to prevent the silver salt from affecting the film image after re-exposure.

The fixing time of the manual punching film is doubled after the photosensitive portion is not transparent on the negative film.

The fixing process of the punching machine is also automatically completed by the automatic punching machine. The mixing ratio of the syrup can be slightly thicker than that of the developing syrup, that is, the fixing syrup of the volume of one measuring cup is evenly mixed with the water of about 3 cups of volume.

4>Washing: The film after fixing is adhered with chemicals such as sodium thiosulfate. If it is not rinsed, the film will turn yellow.

Hand-punched tablets are usually rinsed with running water for 15 to 20 minutes.

The washing and drying process of the machine is automatically completed by the automatic punching machine.

5> Air drying: The film after hand-punching should also be stored in a cool dry place and air-dried.

6> In the above process, be careful not to scratch the film, and do not splash chemical and fixing liquids on the human body and clothing.

2. Film test.

Film testing is generally performed by visual inspection.

1. Appearance inspection.

2. Dimensional inspection of details and details.

3. Inspection of optical density.

4. The simple inspection of the film can be carried out by comparing the line of the same PCB design file, the solder mask and the matching of the character film. The degree of coincidence should be basically consistent with the document observation.

3. The preservation of the film.

For a long time, the dimensional stability of film has been a problem that plagues PCB production. Ambient temperature and relative humidity are the two main factors affecting the size change of the film. The change of the film size deviation is mostly determined by the ambient temperature and relative humidity. The deviation of the total deviation from the ambient temperature and relative humidity is proportional to the size of the film. The larger the size, the larger the deviation.

By controlling the ambient temperature and relative humidity, it is possible to control the deformation of the film. The stability of the ambient temperature and relative humidity is guaranteed to a large extent to ensure the stability of the film size. Thick film (0.175mm~0.25mm) is less sensitive to environmental changes than thin film (0.1mm).

In addition, the preservation and transportation of the film has a great influence on the size of the film. Unopened original film negatives should be stored and transported at a relative humidity of 50% and a temperature of 20 degrees Celsius. Before using the film, the closed seal is opened, and the inner layer package is removed to make it contact with the ambient temperature for a period of time. After the film is painted and punched, it should be wrapped in special film paper as soon as possible and stored and transported in a dry special-sized plastic bag. It is absolutely forbidden to place the film directly in a hot and humid environment, and it is not allowed to perform destructive operations such as bending, folding and stretching of the film.

With the increasing accuracy of printed boards and the increasing density, the film of the film is slightly deformed, which may lead to misalignment and gaps in production. Therefore, it should be ensured that the film has a good environment in transportation, production, storage and use, reducing the temperature and humidity changes, and ensuring the stability of the film size. Otherwise, the change in film size will become a major obstacle to improving the quality of PCB products.

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