How Printed Circuit Boards Are Created
Computer electronic boards are used to house computer circuitry and support the various components of a computer or other electronic device. The board provides structure and keeps parts apart the right amount of distance, preventing shorting out or allowing RF interference. It also protects the circuitry from moisture and other environmental hazards. It replaces much of the complex wiring traditionally required in electrical devices, making it smaller and more portable. Printed circuit boards are available in different sizes and shapes. Single-sided and double-sided boards are common types of PCBs. They can be made with different layers of copper, which carry the electronic signals. Some layers are specialized for power, while others enhance the strength of the circuits.
How do circuit boards work? A printed circuit board is an electro-mechanical assembly that contains the necessary electrical elements to perform its function. These elements include resistors, capacitors, inductors, and diodes. The resistors apply resistance to the electric current that flows through them, limiting its flow and producing voltage. The capacitors store electric charge and release it when needed, while the inductors store energy as a magnetic field and block interference signals within the circuit. The diodes allow only one-way flow of electricity, preventing current from going backward and potentially damaging the computer or other component.
Depending on the complexity of the circuit, it can be designed by hand or using computer-aided design software programs, or CAD. Early designs were done manually by creating a photomask on clear mylar sheets that were two or four times the size of the finished product, with traces routed to connect the component pin pads. Rub-on dry transfers of common footprints on the mylar helped increase efficiency in layout. Then a schematic was drawn with CAD tools to represent the logical circuitry of the computer, and the connections between the component pin pads were shown by wires on the diagram.
The next step in the CAD process is to use the wires on the schematic diagram to create a physical representation of the circuit. This is called the "Schematic Capture" process, and it uses a special tool to create the layout of the parts and the connectivity between them. The schematic is then compared with the circuit simulation model to make sure that it will work as intended.
Once the schematic is complete, the bare circuit board is prepared for manufacturing. Holes are drilled into the bare board where the components will be placed. The bare board is then etched to remove the areas that are not connected, which is accomplished by using chemicals. This leaves behind the copper on the conductive surfaces of the board. This process is repeated to create a "mask" that will protect the sensitive components during assembly.
After the mask is created, the bare board can be plated with copper on both sides, which is known as a "double-sided" circuit board. The component leads can then be soldered to the copper traces on either side of the circuit board. A legend is often printed on one or both sides of the circuit board, showing component designations, switch settings, test points, and other indicators that are helpful when assembling, testing, servicing, and using the final product. The legend is often printed with a silkscreen or liquid photo imaging technique.