Printed circuit (PC) boards grew out of the need to make better military radios during the Second World War. In the post-war era, printed circuit manufacturing took off in the private sector, spurred by the growth of radio and television. Advances in board materials and soldering techniques led to smaller, denser, more capable circuits. Virtually every electronic product, from pocket radios to communications satellites, has been enabled and improved by this technology. Board Traces Components Connectors The traces themselves may also serve as connectors. The board may have an indent cut in it, with thick copper traces terminating at the board's edge. The board's edge itself then serves as a plug-in connector. Most computer cards and memory modules are made to connect this way. Vias
The boards are commonly 1.6 millimeters thick and made of a variety of materials. Older boards have a brown color that comes from phenolic resin and paper. Better quality boards have a green, red, or blue color from epoxy and glass fiber. The material must stand up to mechanical, electrical, and thermal stresses from years of use. It must also be easy to cut and drill.
A copper foil is glued to at least one side of the board. During manufacture, the copper surface is printed with a pattern and exposed parts chemically etched away, leaving thin conductive lines called traces. They're the circuit board's wiring. Components are soldered to the copper traces to form electronic circuits. Depending on their shape and size, traces can also serve as miniature antennas, heat sinks, or connectors.
Electronic components are placed and soldered to one or both sides of the board. The only restrictions on the components are their size, their electrical requirements, and how hot they get. Holes can be cut into the board to accommodate unusually-shaped parts.
To supply power and electrical signals to the board, connectors are attached. They're made of plastic with metal inserts and pins that protrude through the circuit board. The pins are soldered to copper traces, forming a solid connection.
Some circuit boards have copper on one side, some have it on both sides, many have dozens of layers inside the board. The different layers need to be electrically connected at certain points. Vias are holes drilled through the board, and filled with a conducting metal plug that connects the various layers. The use of multiple layers and vias increases circuit density, making possible small, complex devices like cell phones, computer video cards, and mp3 players.
