All electronically controlled devices, such as computers and phones, have one or more circuit boards. A circuit board is what holds different types of electronic components. A circuit board is generally made up of an insulating material, sandwiched between two thin layers of copper. The copper is etched to produce pads where components are installed as well as traces or thin copper strips to connect these components together.
Integrated Circuit Chips
Integrated circuit chips, or ICs, are small-sized devices that are designed to perform specific tasks. These chips range from simple amplifiers to very complicated microprocessors. A circuit board may contain one or more of such chips depending on its design. For example, a computer's main circuit board, also called "motherboard," contains a microprocessor, memory chip ICs, a number of amplifiers and timer chips.
Passive Electronic Components
Passive electronic components are the ones that do not require a power source. Common examples are resistors and capacitors. In most circuit boards, resistors can be found in largest numbers. Since a resistor is a piece of solid that resists flow of electrical current, one of its purposes is to limit the current. For example, if high current can damage the subsequent circuitry, a resistor in the path would limit the current to avoid the damage.
Another use of resistors is to scale-down or decrease voltage, through the so called voltage-divider circuit, which is simply a number of resistors connected in series and parallel in a certain configuration. Resistors are also used in amplifier circuits and as loads. After resistors, capacitors are the second most abundant component found on most circuit boards. Capacitors are mainly used to filter fluctuations in voltages and currents. Other passive components used in PCBs are inductors, diodes, transistors, resonators and crystals.
Some PCBs are equipped with switches to turn them on or off. These switches can be mechanical or electronic. An electronic switch is an active component as it requires power to operate.
Connectors and Terminals
Connectors and terminals are used to connect the PCBs with power supplies and other electronic circuits though cables. They come in different shapes, sizes and types.