Printed circuit board assembly

A printed circuit board populated with electronic components is called a printed circuit assembly, printed circuit board assembly, or PCB assembly (PCBA). In informal usage, the term "printed circuit board" most commonly means "printed circuit assembly" (with components).

Components are generally soldered to the PCB both to connect them electrically and to fix them mechanically. Printed circuit boards are used in almost all electronic products and some electrical products.

Currently, the production and assembly of printed circuits are automated. Electronic computer aided design software is available to do much of the layout work.

Multilayer PCBs allow for much higher component density because the component paths on the inner layers would occupy the space between the components.

The increase in the need for multilayer printed circuit boards with more than two, four and especially more than six layers of copper has been concurrent with the adoption of surface mount technology.

"Through holes" components are assembled by their legs passing through the board and glued to the pads on the other side. "SMD" components are soldered on the same side of the board. A board can use both methods for soldering components. Today PCBs with components mounted only through holes are now less common. Surface mount is used for components like transistors, diodes, IC chips, resistors and capacitors. Through-hole mounting can be used for some large components such as electrolytic capacitors and connectors.