The pcb development operation is generally carried out in the pcb developer machine. Good development effect can be obtained by controlling the development parameters such as developer temperature, transmission speed and spray pressure.
The developer of water-soluble dry film is 1 ~ 2% anhydrous sodium carbonate solution, and the liquid temperature is 30 ~ 40 ℃.The development speed is accelerated with the increase of temperature within the range. The development temperature of different dry films is slightly different, which needs to be adjusted according to the actual situation. Too high temperature will make the film lack toughness and brittle.
The development mechanism is that the active group in the unexposed part of the photosensitive film reacts with the dilute alkali solution to form soluble substances and dissolve them. During development, the active group carboxyl COOH reacts with Na + in anhydrous sodium carbonate solution to form hydrophilic group COONa.Thus, the unexposed part is dissolved, and the dry film of the exposed part is not swollen.
The correct development time is determined by the development point (the point where the unexposed dry film is dissolved from the printed board). The development point must be maintained at a constant percentage of the total length of the development section.If the developing point is too close to the outlet of the developing section, the unpolymerized resist film cannot be fully cleaned and developed, and the residue of the resist may remain on the plate surface.If the development point is too close to the inlet of the development section, the polymerized film may be etched and become hairy and lose luster due to prolonged contact with the developer.Generally, the development point is controlled within 40% ~ 60% of the total length of the development section.
When the developer is in use, there will be a lot of bubbles due to the continuous spraying and stirring of the solution, so an appropriate amount of defoamer must be added.Such as n-butanol, special defoamer AF-3 for printed board, etc.The addition amount of defoamer starting is about 0.1%. With the developing solution dissolving into the dry film, the foam will increase, and it can be added continuously.Some developers have a device to automatically add defoamer.After development, ensure that there is no residual glue on the plate surface to ensure good adhesion between the base metal and the electroplated metal.
During the development process, sodium carbonate needs to be supplemented continuously. In some cold weather areas, during the development in winter, the medicine barrel supplemented with sodium carbonate shall be equipped with a heating device to prevent poor development due to the temperature drop caused by the supplement of liquid medicine in the development section.
It is difficult to see whether there is residual glue on the plate surface after development. It can be checked with 1% methyl violet alcohol aqueous solution or 1 ~ 2% sodium sulfide or potassium sulfide solution. There is no color change after dyeing with methyl violet and immersion in sulfide, indicating that there is residual glue.
Oct. 15, 2021 
