Electronic Design - Do you know how to learn an introductory PCB circuit board?

1. Appearance inspection.

The appearance inspection of film generally does not need to be magnified, and the visual inspection should qualitatively check the mark, appearance, PCB process quality and graphics of the film. Visual inspection should be performed with naked eyes (standard vision, normal color perception) at the most favorable observation distance and suitable lighting, without magnification. Qualified negatives should be finely processed and processed, smooth in appearance, free of wrinkles, cracks and scratches, and clean, free of dust and fingerprints.

2. Details and size inspection of details.

In the detailed inspection, a special optical instrument with a linear magnification of about 10 times or more than 100 times, a measuring scale and reading can be used to check whether there are wire defects (such as pinholes and edge gaps, etc.) and whether there are dirty spots between the wires. And the measurement error of the instrument should not be greater than 5%. When inspecting the size of a distance greater than 25mm, a grid glass plate with precise graduations can be used.

3. Inspection of optical density.

Optical density refers to the transmitted optical density. The transparent part and the opaque part can be measured with an ordinary densitometer during inspection. The measuring area is 1mm in diameter. When the requirements are not high, the visual comparison method can be used for inspection. During the inspection, the transparent and opaque parts are compared with a standard gray copy base plate or gray calibration copy base plate.

4. The simple inspection of the film can be carried out by observing and comparing the coincidence degree of the circuit, solder mask and character film of the same PCB design file. The degree of coincidence should be basically consistent with the file observation. Be careful not to touch the film directly with your hands during this process, so as not to scratch the film with your nails and leave dust and fingerprints on the film.

Three>, the custody of the film.

For a long time, the dimensional stability of film has been a problem that plagued PCB production. Ambient temperature and relative humidity are the two main factors that affect film size changes. Most of the changes in film size deviation are determined by ambient temperature and relative humidity. The deviation of the total deviation affected by the ambient temperature and relative humidity is proportional to the size of the film. The larger the size, the greater the deviation.

Through the control of the ambient temperature and relative humidity, the deformation of the film can be controlled. Ensuring the stability of the ambient temperature and relative humidity ensures the stability of the film size to a large extent. 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 negative. Unopened original film negatives should be stored and transported under the conditions of 50% relative humidity and 20 degrees Celsius. Before using the film, open the airtight seal, remove the inner packaging, and keep it in contact with the ambient temperature for a period of time. After the film is drawn and punched, it should also be wrapped in special film paper and placed in a dry special-sized plastic bag for storage and transportation as soon as possible. It is absolutely forbidden to put the film directly in a hot and humid environment, and it is not allowed to perform destructive operations such as bending, folding and stretching the film.

With the increasing demands on the precision of printed boards and the increasing density, a slight deformation of the film negatives may cause dislocations and gaps during production. Therefore, it is necessary to ensure that the film has a good environment during transportation, production, storage and use, reduce temperature and humidity changes, and ensure the dimensional stability of the film. Otherwise, the change of film size will become a major obstacle to improving the quality of PCB products.