Printed circuit boards (PCBs) are found in all but the simplest electronic devices. These boards mechanically support electronic components, while electrically connecting them with copper tracks, pads, and other parts. Manually etching the circuit, via chemical or mechanical methods, becomes a viable option when making a test PCB or a few pieces. The type of PCB etching products required depends on the method.
Printed Circuit Boards
Both chemical and mechanical etching processes start with a plain copper-clad circuit board. The etching process removes unnecessary copper, leaving the circuit on the board in copper. Photosensitive boards have a protective layer of "resist" that is sensitive to UV light. This type requires a developer, usually a solution of sodium hydroxide. Though most boards have a fibreglass substrate, they are available with different substrate materials and in different thicknesses.
Mechanical etching requires a machine tool, such as a CNC milling machine, and special cutters. The machine mechanically removes strips of copper from the board, leaving the final circuit in place. Since this process requires specialised and expensive equipment, hobbyists often do not go this route nor use it to make a small batch of PCBs.
The most common method, chemical etching involves masking the circuit design with an etch resist that is resistant to the etchant, a corrosive chemical that removes the copper layer. Photosensitive boards have a precoat of resist. Users should coat other boards themselves. For simple circuits, ink applying resist with a permanent marker works. However, software and printers are essential for more complicated circuits. Designs printed on photo paper using both inkjet and laser printers with at least a 600 DPI resolution can transfer onto boards, thereby providing a layer of resist. The board is then soaked in etchant, leaving only the resist-coated circuit in place. Photosensitive PCB boards require one additional step. The design is first printed on translucent or transparent sheets and affixed to the board, which is then exposed to UV light. Developing removes the coating of resist from all areas, except those masked by the design. The etchant then removes unprotected copper. A number of chemicals can serve as etchant, including ammonium persulphate, sulphuric acid, and ferric chloride, with the last being cheap and easily accessible.
Since chemical etching involves working with dangerous chemicals, users should take necessary safety precautions. Wear safety goggles, gloves, and aprons to protect skin and eyes from permanent damage, especially when handling ferric chloride, which can form clumps and splash into the etchant solution.