All electronic devices, such as computers, cell phones and televisions, use printed circuit boards (PCBs). The printed circuit board holds the transistors, resistors and integrated circuit components that make the device work. The board material is usually made of an epoxy fiberglass plastic. On the board, printed copper foil patterns electrically connect the components, forming circuits. PCBs have helped make modern electronics compact, reliable and inexpensive.
Single Side
The simplest kind of printed circuit board has a single layer of copper on one side. The components usually sit on the opposite side. Holes in the circuit board accommodate component leads, which are soldered to small, round pads formed in the copper foil. Electronic hobby kits use single-sided boards, as they are easy to assemble by hand.
Multilayer
A multilayer circuit board has layers of copper foil and fiberglass. Each copper foil layer has a different pattern on it, creating a complex three-dimensional circuit. While more difficult to design PCB, multilayer boards allow for denser circuits and a smaller, more sophisticated product. These boards are manufactured by machine in large quantities.
Thru-Hole
Some circuit boards have components with leads. The leads are stiff wires bonded to the component that carry electronic signals in and out of the part. A technician or machine inserts the leads through the holes in the board, solders them on the foil side and clips them flush with the board. The components all mount on one side of the board called the component side.
Surface Mount
In the 1980s, electronics manufacturers adopted surface-mount components for many products. These components do not have leads; they solder directly to the surface of the circuit board's copper foil. While the circuit boards might still have holes for other purposes, they no longer needed to have holes drilled for components. Surface mount circuit boards cost less and can pack more components than the older thru-hole technology.
