A circuit board contains a collection of components (surface mounted devices or SMD’s) and through hole components connected to each other for a specific purpose. These can range from computer and mobile phone circuits to simple electrical motor control circuitry. All of these components are connected by wires made from conductive materials such as copper and aluminum. In addition, circuit boards contain insulating materials such as epoxy and fiberglass. The design of a PCB begins with a schematic, a blueprint of the electrical circuitry on the board. The design is then translated into a physical layout using a computer-aided design program, also known as a CAD system.
The first PCBs were produced in the early 1900s, but they were not widely used until after World War II, when the U.S. military adapted a British device, the proximity fuse, to enhance artillery shells so they could hit their targets more accurately. The proximity fuse was a printed circuit board that allowed soldiers to wire up the components on the front of the gunner’s rifle with a single lever or button, thus eliminating the need for manual soldering of individual wires. In order to scale up production, the U.S. Army looked for ways to print actual electronic circuits on the surface of a piece of paper, and in 1947, German inventor Paul Eisler received a patent for a printed circuit board.
During the process of creating a printed How do circuit boards work, an insulating material is applied to one side of the PCB and copper is deposited on its opposite. A pattern, usually a mirror image, is printed on the circuit board using photoresist, which is coated over the copper layers and exposed to light in the pattern of the artwork. Once the patterns are etched, the copper is removed and the circuit board is cleaned.
A legend (also known as silk or silkscreen) is often printed on one or both sides of a PCB to identify component designations, switch settings and test points. It is traditionally printed with screen printing epoxy ink, but liquid photo imaging and ink jet printing are increasingly being used. The latter methods can even print variable data that is unique to each circuit board, such as a bar code with a serial number.
Once the components are placed on the board, a process called routing converts the rubber-band net connections in the schematic into drawn traces and planes on the computer-aided design system. This step requires great care to ensure that the routes are of the correct length for the signals they are conducting and that they do not cross areas of excessive noise. It is a skill that is learned over time by experienced circuit board designers.
Printed circuit boards are recyclable, and recycling them reduces the amount of waste in landfills and prevents toxic chemicals from leaching into the environment. The recycled metals can be repurposed and sold, generating revenue for the recycling industry and reducing the need for new resources to be mined.