printed circuit board

hardware (PCB) A thin board to which electronic components

are fixed by solder. Component leads and integrated circuit

pins may pass through holes ("vias") in the board or they may

be surface mounted, in which case no holes are required

(though they may still be used to connect different layers).

The simplest kind of PCB has components and wires on one side

and interconnections (the printed circuit) on the other. PCBs

may have components mounted on both sides and may have many

internal layers, allowing more connections to fit in the same

board area. Boards with internal conductor layers usually

have "plated-through holes" to improve the electrical

connection to the internal layers.

The connections are metal strips (usually copper). The

pattern of connections is often produced using photo-resist

and acid etching. Boards, especially those for high frequency

circuits such as modern microprocessors, usually have one or

more "ground planes" and "power planes" which are large

areas of copper for greater current carrying ability.

A computer or other electronic system might be built from

several PCBs, e.g. processor, memory, graphics controller, disk

controller etc. These boards might all plug into a

motherboard or backplane or be connected by a ribboncable.

(1995-05-01)