What should we do if the PCB dry film occur broken or diffusion coating
With the rapid development of the electronics industry, PCB layout is becoming more and more sophisticated. Most PCB manufacturers use dry film to complete graphics transfer. The usage of dry film is becoming more and more popular, but many customers still encounter many problems when using dry film. Misunderstandings are now summarized for reference.
First.,dry film masking holes appear broken
Many customers believe that after the occurrence of broken holes, the film temperature and pressure should be increased to enhance the bonding force. In fact, this view is incorrect. Because the temperature and pressure are too high, the solvent of the resist layer is excessively volatilized and dried. So that the dry film becomes brittle and thin, and it is easy to be broken through the hole during development. We have to always maintain the toughness of the dry film. Therefore, after the hole is broken, we can improve from the following points:
1, Reduce filming temperature and pressure
2, Improve the drilling cloak
3, Increase exposure energy
4, Reduce the development pressure
5, The parking time after filming can not be too long, so as not to cause the semi-fluid film at the corner to spread and become thin under the pressure
6, The dry film should not be too tight during the filming process
Second, the appearance of diffusion coating during dry film plating
The reason why the diffusion coating is carried out indicates that the dry film and the copper clad plate are not firmly bonded, so that the plating solution is deep in, and the plating layer of the “negative phase” is thickened. The diffusion coating of most PCB manufacturers is caused by the following points:
1, The exposure energy is too high or too low
Under ultraviolet light irradiation, the photoinitiator that absorbs the light energy decomposes into free radical to initiate a photopolymerization reaction to form bulk molecule which is insoluble in a solution of dilute alkali. When the exposure is insufficient, due to incomplete polymerization, during the development process, the film swells and becomes soft, resulting in unclear lines or even peeling off of the film, resulting in poor bonding of the film and copper; if overexposed, it may cause development difficulties and also produce warp peeling during the plating process, forming a plating .So it is important to control the exposure energy.
2, The filming temperature is too high or too low
If the filming 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 volatiles in the resist compound may be caused the rapid evaporation of the substance which generates bubbles, and the dry film becomes brittle, forming a warp peeling during electroplating, causing diffusion coating.
3, The filming pressure is too high or too low
When the attaching film pressure is too low, the film surface may be uneven or gap may be formed between the dry film and the copper plate to meet the bonding force requirement; if the film pressure is too high, the solvent and volatile components of the resist layer are excessively volatilized, resulting in excessive evaporation. The dry film becomes brittle and will peel off after electroplating.
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