There is no standard printed circuit board. Each printed circuit board has a unique function for a particular product and must be designed to perform that function in a dedicated location. PCB designers use computer-aided design systems with special software to lay out the required circuit. The gaps between electrically conductive media are often 0.04 inches (1.0 mm) or less. The location of holes for component wires or contact points is also determined, and this information is translated into instructions for computer numerical control or automatic solder paste used in the manufacturing process.
The most commonly used substrate in printed circuit boards is fiberglass-reinforced (fiberglass) epoxy resin with copper foil bonded on one or both sides. Printed circuit boards made of paper-reinforced finel resin with glued copper foil are less expensive and are often used in household electrical appliances.
The printed circuit boards are made of copper, which is either coated or engraved on the surface of the substrate to retain the desired pattern. Copper chains are coated with a tin-lead layer to prevent oxidation. The contact elements are coated with tin lead, then nickel and finally gold to ensure excellent conductivity.
The processing and assembly of printed circuit boards is carried out in a particularly clean environment where air and components cannot be contaminated. Many electronics manufacturers have their own patented processes, but these steps can typically be used to make a double-sided printed circuit board.
The circuit board scheme can be created using an "add-on" or "subtraction" process. During the additive process, the copper is coated or added to the substrate surface of the printed circuit board in the desired pattern, leaving the remaining surface uncovered. The subtraction process first covers the entire surface of the substrate and then engraves or subtracts areas that are not part of the desired pattern.