In the current printed circuit board (PCB) processing, the common method is the “pattern plating method.” This involves pre-plating a layer of lead-tin anti-corrosion on the copper foil section that needs to remain on the outer layer, known as the circuit pattern. The remaining copper foil is then chemically corroded through etching, resulting in two copper layers on the board. During outer layer etching, one copper layer must be completely removed, leaving the final circuit. This pattern electroplating method only has copper plating under the lead-tin resist layer.
Another process is the “full board copper plating process,” where copper is plated on the entire board except for parts covered by photosensitive film. This method requires double plating and etching of all parts of the board, causing issues with fine wire widths and side corrosion affecting line uniformity.
In the outer circuit processing of PCBs, a method using photosensitive film as the resist layer is also used, similar to inner layer etching processes. Ammonia-based etchants are commonly used with tin or lead-tin anti-corrosion layers. Ammonia etchants such as ammonia/ammonium chloride or ammonia/ammonium sulfate solutions are widely available.
Sulfate-based etching solutions allow for copper separation for reuse through electrolysis due to their low corrosion rate, although they are less common in production. Sulfuric acid-hydrogen peroxide etchants have been tried but are not widely used commercially due to cost and waste treatment issues, especially for lead-tin resist etching.
Equipment adjustment and interaction with corrosive solutions are crucial in ammonia etching processing. Maintaining continuous working status and selecting the proper nozzle structure and spray method are essential for high-quality etching results. The etching rate in ammonia etching is based on ammonia concentration, emphasizing the need for fresh solutions to flush out copper ions and provide ammonia for the reaction.
Controlling monovalent copper ions in ammonia etching solutions is key for faster reaction speeds, with additives used to reduce monovalent copper ions. Introducing oxygen to convert monovalent copper to divalent copper helps maintain low monovalent copper content, with the need for controlled airflow to prevent loss of ammonia. Methods like adding pure ammonia and PH meter control systems help maintain solution stability.
Research in chemical etching has progressed to machine structure design for divalent copper solutions, offering potential benefits in the printed circuit industry. In the photochemical etching industry, stringent parameters are required for etching thick copper foils, with higher standards than in the PCB industry.
Another process is the “full board copper plating process,” where copper is plated on the entire board except for parts covered by photosensitive film. This method requires double plating and etching of all parts of the board, causing issues with fine wire widths and side corrosion affecting line uniformity.
In the outer circuit processing of PCBs, a method using photosensitive film as the resist layer is also used, similar to inner layer etching processes. Ammonia-based etchants are commonly used with tin or lead-tin anti-corrosion layers. Ammonia etchants such as ammonia/ammonium chloride or ammonia/ammonium sulfate solutions are widely available.
Sulfate-based etching solutions allow for copper separation for reuse through electrolysis due to their low corrosion rate, although they are less common in production. Sulfuric acid-hydrogen peroxide etchants have been tried but are not widely used commercially due to cost and waste treatment issues, especially for lead-tin resist etching.
Equipment adjustment and interaction with corrosive solutions are crucial in ammonia etching processing. Maintaining continuous working status and selecting the proper nozzle structure and spray method are essential for high-quality etching results. The etching rate in ammonia etching is based on ammonia concentration, emphasizing the need for fresh solutions to flush out copper ions and provide ammonia for the reaction.
Controlling monovalent copper ions in ammonia etching solutions is key for faster reaction speeds, with additives used to reduce monovalent copper ions. Introducing oxygen to convert monovalent copper to divalent copper helps maintain low monovalent copper content, with the need for controlled airflow to prevent loss of ammonia. Methods like adding pure ammonia and PH meter control systems help maintain solution stability.
Research in chemical etching has progressed to machine structure design for divalent copper solutions, offering potential benefits in the printed circuit industry. In the photochemical etching industry, stringent parameters are required for etching thick copper foils, with higher standards than in the PCB industry.
