Load balancers, printers, elevators, phones, and almost all electrical devices rely on them to carry current to and from their components. They are made of copper traces, which help electronic signals communicate properly.
The PCB is typically printed with a legend, containing the component designators, switch settings, and other indications needed to assemble, test, and use a piece of electronic hardware. The legend is usually silkscreened with epoxy ink, although liquid photo imaging is becoming more common. The silkscreen is most often white, but black, gray, red, yellow, or any other ink color is possible as well.
There are two main methods of creating a PCB: additive and subtractive. In an additive process, the bare laminate is covered with a photosensitive film that is imaged (exposed to light through a mask and then developed) to make it capable of bonding metal ions. The copper pattern is then plated onto the substrate in its sensitized areas. The rest of the unmasked area is then etched and sanded to produce a rough surface that can accept solder. Tin-lead and other surface platings are then applied to the sanded area to provide conductivity.
After the copper pattern is deposited, holes are drilled on the board where the components will be placed. A specialized drill can be used to ensure the holes are of the proper size, spacing, and location for the given application. The resulting bare board is then etched again to remove any areas of the copper that aren’t intended for use in the final product. The etching process also removes any tin-lead and other surface plating that may have been applied.
How do circuit boards work is now ready for the component installation and soldering process. Once the components are in place and soldered, the board can undergo various inspections to ensure that all the parts have been positioned correctly and that everything is working as it should. This includes visual inspection and automated optical inspection, both of which are commonly used by manufacturers to maintain quality control in this critical phase of the manufacturing process.
A PCB can be powered by either a DC current (which is steady and only flows in one direction), or AC current (which fluctuates from negative to positive). Most modern devices use an AC power supply, but many still operate on DC power.
A PCB is typically composed of several layers of dielectric composite materials that have a resin matrix with a woven and/or nonwoven fiberglass reinforcement, and sometimes other fillers. The most common dielectric material is FR-4, which has a very low water absorption and very good insulation properties. FR-4 is available in many thicknesses; 0.1 oz copper per square foot (35 um) is the most common, but thicker options are available as well. Other types of dielectric materials have different characteristics that can be desirable for specific applications.