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With the rapid development of the electronic industry, PCB wiring is becoming more and more precise. Most PCB manufacturers use dry film to complete pattern transfer, and the use of dry film is becoming more and more popular. However, in the process of after-sales service, I still encounter many misunderstandings when using dry film, which are summarized for reference.

1、 The dry film mask is broken:

Many customers believe that after a hole is broken, the film temperature and pressure should be increased to enhance its adhesion. In fact, this view is incorrect, because when the temperature and pressure are too high, the solvent of the resist layer volatilizes excessively, which makes the dry film brittle and thin, and it is very easy to break through the hole during development. We should always maintain the toughness of the dry film. Therefore, after a hole is broken,We can make improvements from the following points:

• Reduce the film temperature and pressure.
• Improve the drilling front
• Increase exposure energy
• Reduce development pressure
• The parking time after coating shall not be too long, so as not to cause the semi fluid film at the corner to diffuse and thin under the action of pressure
•  Do not stick the dry film too tightly during film application

2、 Infiltration during dry film plating:

The reason for infiltration plating is that the dry film is not firmly bonded to the copper-clad laminate, which makes the plating solution go deep, resulting in the thickening of the coating in the “negative phase”. Infiltration plating in most PCB manufacturers is caused by the following points:

•  High or low exposure energy.

Under UV irradiation, the photoinitiator absorbing light energy is decomposed into free radical initiator monomers for photopolymerization to form body molecules insoluble in dilute alkali solution.In case of insufficient exposure, due to incomplete polymerization, the adhesive film swells and softens in the development process, resulting in unclear lines and even film falling off, resulting in poor combination between the film and copper;If the exposure is excessive, it will cause development difficulties, and will also produce warping and peeling in the electroplating process, forming infiltration plating.Therefore, it is important to control the exposure energy.

•  The film temperature is too high or too low.

If the coating temperature is too low, the adhesion between the dry film and the copper-clad laminate surface is poor due to the insufficient softening and proper flow of the resist film;If the temperature is too high, bubbles will be generated due to the rapid volatilization of solvent and other volatile substances in the photoresist, and the dry film becomes brittle, resulting in warping and stripping during electroplating electric shock, resulting in infiltration plating.

• Film pressure too high or too low.

When the film pressure is too low, the film surface may be uneven or there may be a gap between the dry film and the copper plate, which may not meet the requirements of bonding force;If the coating pressure is too high, the solvent and volatile components of the resist layer volatilize too much, resulting in the embrittlement of the dry film, which will warp and peel off after electroplating electric shock.