In PCB manufacturing, the production of outer circuit layers is a crucial step, involving multiple processes such as pretreatment, lamination, exposure, development, etching, film removal, and post-processing. The following is a detailed technical introduction:
Pretreatment: Mechanical grinding and brushing combined with chemical micro-etching (medium coarsening or ultra-coarsening) are adopted to remove impurities such as oxides and oil stains on the copper surface, ensuring good adhesion in subsequent processes. The concentration, temperature and processing time of the cleaning solution must be strictly controlled to avoid over-cleaning or incomplete cleaning.
Lamination: Evenly laminate the dry film onto the PCB surface. The selection of the dry film should be based on the design requirements and process characteristics of the PCB to ensure it has good resolution, adhesion and corrosion resistance. The pressure, temperature and speed of film pressing are key parameters that need to be precisely controlled to ensure a tight bond between the dry film and the copper surface.
Exposure: Select the appropriate exposure machine based on the chosen dry film. For instance, LDI dedicated dry film requires an LDI machine, while ordinary dry film can be exposed with a CCD exposure machine. The pre-designed circuit pattern is projected onto the PCB with a dry film through a photomask to cause a chemical reaction in the dry film. Exposure energy, time and alignment are important factors affecting exposure quality.
Developing: Use the developing solution to remove the unexposed dry film to expose the copper surface to be etched. The concentration, temperature and development time of the developer must be strictly controlled to ensure the accuracy and integrity of the graphics. After development, the PCB needs to be inspected to promptly identify and address any issues of poor development.
Etching: After the PCB has been developed, it is placed in an acidic etching solution to etch away the copper that has not been protected by a dry film, forming circuit patterns. The composition, temperature and etching speed of the etching solution are key parameters that need to be adjusted according to different PCB designs and materials. Close attention should be paid to the etching effect to prevent over-etching or under-etching.
Demolding: After etching is completed, the dry film is removed with the demolding solution to expose the final circuit pattern.
Post-processing: It includes cleaning, drying, anti-oxidation treatment and other steps to ensure the appearance and performance of the PCB. The composition and temperature of the cleaning solution, as well as the drying time and temperature, must be strictly controlled.
