The copper foil substrate is first cut into sizes suitable for processing and production. Before lamination, the copper foil on the substrate surface is typically roughened using methods such as brushing and micro-etching. Dry film photoresist is then adhered to the substrate using the appropriate temperature and force. The substrate with the dry film photoresist is then placed in a UV exposure machine for exposure. The UV light in the transparent areas of the film causes a polymerization reaction (the dry film in these areas will be retained as etch resistance in the subsequent development and copper etching steps), transferring the circuit image from the film to the dry film photoresist on the board surface. After removing the protective film from the film, the unexposed areas are first de-wetted with a sodium carbonate solution. The exposed copper foil is then etched away with a mixture of hydrochloric acid and hydrogen peroxide to form the circuitry. Finally, the dry film photoresist is removed with a sodium hydroxide solution. For inner layer circuit boards with six or more layers, an automatic positioning punch is used to punch reference holes for interlayer circuit alignment.
