What is PCB dry film?

The rapid development of science and technology continues to promote the rapid development of the electronics industry. PCB wiring is becoming more and more precise. Most PCB manufacturers use dry film to complete pattern transfer. The use of dry film is becoming more and more popular, but there are still many customers. There are many misunderstandings when using dry film, which are summarized here for reference.

1. Holes appear in dry film masking

Many customers believe that after holes appear, the temperature and pressure of the film should be increased to enhance its bonding force. In fact, this view is incorrect because when the temperature and pressure are too high, the solvent of the resist layer will evaporate excessively, causing the dry The film becomes brittle and thin, and can easily be punctured during development. We must always maintain the toughness of the dry film. Therefore, after holes appear, we can make improvements from the following points:

1. Reduce the film temperature and pressure

2. Improve the drilling tip

3. Increase exposure energy

4. Reduce development pressure

5. The parking time after applying the film should not be too long, so as not to cause the semi-fluid film at the corners to spread and become thinner under the action of pressure.

6. Do not stretch the dry film too tightly during the film application process.

2. Bleeding occurs during dry film plating

The reason for seepage plating indicates that the dry film and the copper-clad foil board are not firmly bonded, allowing the plating solution to penetrate deeply, causing the "negative phase" part of the coating to become thicker. Most PCB manufacturers see seepage plating due to the following points:

1. Exposure energy is too high or too low

Under ultraviolet light irradiation, the photoinitiator that has absorbed light energy decomposes into free radicals to initiate monomers for photopolymerization, forming body molecules that are insoluble in dilute alkali solutions. When the exposure is insufficient, due to incomplete polymerization, the film swells and becomes soft during the development process, resulting in unclear lines and even peeling off of the film, resulting in poor bonding between the film and copper; overexposure will cause difficulty in development, and will also cause problems in the electroplating process. Warping and peeling occur in the process, forming infiltration plating. So it is important to control the exposure energy.

2. The film temperature is too high or too low

If the laminating temperature is too low, the resist film will not be fully softened and flow properly, resulting in poor bonding force between the dry film and the copper-clad laminate surface; if the temperature is too high, the solvent and other volatile components in the resist will The rapid volatilization of substances produces bubbles, and the dry film becomes brittle, causing warping and peeling during electroplating shock, resulting in seepage plating.

3. The film pressure is too high or too low

When the laminating pressure is too low, it may cause the laminating surface to be uneven or create a gap between the dry film and the copper plate, which cannot meet the bonding force requirements; if the laminating pressure is too high, the solvent and volatile components of the resist layer will volatilize too much, resulting in The dry film becomes brittle and will warp and peel off after electroplating shock. The above is a summary of misunderstandings about PCB dry films, which cannot be separated from the continuous efforts of engineers in practice.