Printed circuit boards are independent modules of interconnected electronic components, always found in devices ranging from common buzzers, pagers, radios to complex radar and computer systems. The circuit is formed by depositing or printing a thin layer of conductive material on the surface of an insulating board known as the substrate.
Individual electronic components are placed on the substrate surface and soldered to the interconnected circuitry. The contact fingers along one or more edges of the substrate serve as connectors to other PCBs or external electrical devices like on-off switches. The printed circuit board may have circuitry that performs multiple functions or a single function like a signal amplifier.
Printed circuit board structure has three main types: single-sided, double-sided and multilayer. Single-sided panels have components on one side of the substrate. When components number on a single-sided board is excessive, a double-sided board can be used. Electrical connections between the circuits on each side are made by drilling holes through the substrate at appropriate locations and plating the interior of the holes with a conductive material. The third type, multilayer board, has a substrate composed of a printed circuits separated by insulated layers. The surface components connect to the appropriate circuit layer through plated holes. This greatly simplifies the circuit mode.
Components on a printed circuit board are electrically connected to the circuit in two different ways: through hole technology and surface mount technology. With through-hole technology, each component has thin wires or leads that pass through the holes in the substrate and are soldered to the connection pads on the opposite side. Gravity and friction between leads and hole sides keep the assembly components in place until they are soldered.
Using surface mount technology, stubby J-shaped or L-shaped legs on each component make direct contact with the printed circuits. A solder paste consisting of glue, flux and solder is applied at the contact points to hold the assembly components in place until the solder melts or reflows in the oven for the final connection. Although surface mount technology requires more attention to component placement, it eliminates the time-consuming drilling process and space-consuming connection pads inherent with through hole technology. Both technologies are in use today. Therefore, it is used more widely than through-hole technology currently.
The other two types of circuit assemblies are related to the printed circuit board. Integrated circuits, also known as ICs or microchips, perform similar functions to printed circuit boards except that integrated circuits have more circuits and components. The hybrid circuit, as its name implies, looks like a printed circuit board but contains some components that grow on the surface of the substrate instead of being placed and soldered on the surface.