A circuit board is a flat piece of electronic board with electrically conductive pathways known as traces that connect electronic components such as transistors, capacitors, resistors and diodes. These connections are made by copper traces and can be printed on one or both sides of the circuit board. The traces on the circuit board are designed to be kept as short as possible to prevent energy losses. The circuit board also provides a platform for adding and replacing parts as needed.
Almost all modern devices, from computers to phones and printers, have a circuit board. The most complex of these are computer electronic boards, which contain components such as microprocessors that operate at very high speeds.
The first step in making a PCB is to make the substrate, the base material that all other elements sit on. Typically this is made of fiberglass, although it can be replaced with another material if budget constraints are an issue.
After the substrate is made, the copper-plated conductive pathways are printed on it. This can be done with a subtractive or an additive process. Subtractive processes use a mask to expose the areas that will be the conductive pathways on the circuit board and then adds copper. The plated copper is often gold or nickel to increase the conductivity of the circuit board. The plated copper may also be coated with dielectric materials, such as polytetrafluoroethylene (PTFE) or polyimide.
A subtractive PCB can be used for components that require a larger contact surface area, such as those that are very tall or wide. In these cases, the conductive pattern can be extended out from the edges of the board to provide more contact surface area. Alternatively, the circuit board can be etched to create more space between the conductive traces for more flexibility.
The most common PCBs are constructed using an additive process. The original copper-clad laminate has a thin layer of metal already on it, so a mask is applied that leaves the bare areas exposed to be patterned with the conductive traces. This layer of copper is usually 1 oz per square foot (35 um) thick, but can be much thinner or heavier for specific applications.
How do circuit boards work is finished, it can be labeled with information such as component designators, switch settings and test points. This information is known as the legend and can be printed on either side of the circuit board. It was traditionally printed with silkscreening epoxy ink, but liquid photo imaging and ink jet printing are now becoming more popular.
The next step is to solder the components on the circuit board. This can be done with through hole or surface mount technology. Through-hole technology was first developed in the 1960s and became more popular in the 1980s. Through-hole components have wire leads that come off the bottom of the device and are inserted into holes on the circuit board. Surface mount technology, on the other hand, was introduced in the 1960s and quickly gained popularity in the early 1980s. This method allows components to be mounted directly onto the conductive surfaces on the circuit board instead of requiring the wires to pass through the holes.