How to improve PCB dry film hole / plating problem
With the rapid development of the electronics industry, PCB layout has become more and more complicated. Most PCB manufacturers use dry film to complete the graphics transfer. The use of dry film is becoming more and more popular, but many customers have many misunderstandings when using dry film:
1. Dry film covering hole rupture
Many customers believe that after a hole has occurred, the temperature and pressure of the film should be increased to enhance the adhesion. In fact, this view is not true. Since the temperature and pressure are too high, the solvent of the resist is excessively volatilized and dried. The film becomes brittle and thin and easily breaks during development. We always have to maintain the toughness of the dry film. Therefore, after the hole, we can improve from the following points:
1) reduce film temperature and pressure
2) improve the cloak of the drill
3) increase exposure energy
4) reduce development pressure
5) the parking time after shooting can not be too long, so as not to cause the semi-fluid film at the corner to spread and become thin under pressure
6) the dry film should not be too tight during the shooting
2. Oxidation during dry film plating
The reason for the electroplating indicates that the dry film and the copper clad plate are not firmly bonded, so the plating solution is deep, and the "negative phase" plating layer becomes thick. Electroplating by most PCB manufacturers is caused by the following:
1）the exposure energy is high or low
Under ultraviolet light, the photoinitiator that absorbs light energy decomposes into free radicals to initiate photopolymerization, forming bulk molecules that are insoluble in the dilute alkali solution. When the exposure is insufficient, due to incomplete polymerization, the film expands and softens during development, resulting in unclear or even peeling of the film lines, resulting in poor adhesion of the film to copper; if overexposed, it may cause development difficulties. It can also lead to the plating process. The warp peeling occurs in the formation and a plating layer is formed. Therefore, controlling the exposure energy is very important.
2） the film temperature is high or low
If the film temperature is too low, the surface of the dry film and the copper clad laminate may be poorly bonded due to insufficient softening and proper flow of the resist film; if the temperature is too high, the solvent and other solvents in the resist may be caused. Volatile. The rapid evaporation of the substance produces bubbles, and the dry film becomes brittle, forming warpage and peeling during the plating process, causing electroplating.
3）the film pressure is high or low
When the membrane pressure is too low, the membrane surface may be uneven or a gap may be formed between the dry film and the copper plate to meet the adhesion requirement; if the membrane pressure is too high, the solvent and volatile components of the resist layer are excessively volatilized , causing excessive evaporation. The dry film becomes brittle and peels off after plating.