Printed circuit board
Tools
From Wikipedia, the free encyclopedia
Not to be confused with Printed electronics.
"PC board" redirects here. For the mainboard of personal computers, see Motherboard.
Printed circuit board of a DVD player.
Part of a 1984 Sinclair ZX Spectrum computer board, a printed circuit board, showing the conductive
traces, the through-hole paths to the other surface, and some electronic components mounted
using through-hole mounting
A printed circuit board (PCB), also called printed wiring board (PWB), is a medium used to connect or
"wire" components to one another in a circuit. It takes the form of a laminated sandwich structure
of conductive and insulating layers: each of the conductive layers is designed with an artwork
pattern of traces, planes and other features (similar to wires on a flat surface) etched from one or
more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive
substrate.[1] Electrical components may be fixed to conductive pads on the outer layers in the shape
designed to accept the component's terminals, generally by means of soldering, to both electrically
connect and mechanically fasten them to it. Another manufacturing process adds vias, plated-
through holes that allow interconnections between layers.
Printed circuit boards are used in nearly all electronic products. Alternatives to PCBs include wire
wrap and point-to-point construction, both once popular but now rarely used. PCBs require
additional design effort to lay out the circuit, but manufacturing and assembly can be automated.
Electronic design automation software is available to do much of the work of layout. Mass-producing
circuits with PCBs is cheaper and faster than with other wiring methods, as components are
mounted and wired in one operation. Large numbers of PCBs can be fabricated at the same time,
and the layout has to be done only once. PCBs can also be made manually in small quantities, with
reduced benefits.[2]
PCBs can be single-sided (one copper layer), double-sided (two copper layers on both sides of one
substrate layer), or multi-layer (outer and inner layers of copper, alternating with layers of
substrate). Multi-layer PCBs allow for much higher component density, because circuit traces on the
inner layers would otherwise take up surface space between components. The rise in popularity of
multilayer PCBs with more than two, and especially with more than four, copper planes was
concurrent with the adoption of surface mount technology. However, multilayer PCBs make repair,
analysis, and field modification of circuits much more difficult and usually impractical.
The world market for bare PCBs exceeded $60.2 billion in 2014[3] and is estimated to reach $79
billion by 2024.[4][5]
History
Predecessors
An example of hand-drawn etched traces on a PCB
Before the development of printed circuit boards, electrical and electronic circuits were wired point-
to-point on a chassis. Typically, the chassis was a sheet metal frame or pan, sometimes with a
wooden bottom. Components were attached to the chassis, usually by insulators when the
connecting point on the chassis was metal, and then their leads were connected directly or with
jumper wires by soldering, or sometimes using crimp connectors, wire connector lugs on screw
terminals, or other methods. Circuits were large, bulky, heavy, and relatively fragile (even
discounting the breakable glass envelopes of the vacuum tubes that were often included in the
circuits), and production was labor-intensive, so the products were expensive.
Development of the methods used in modern printed circuit boards started early in the 20th
century. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an
insulating board, in multiple layers. Thomas Edison experimented with chemical methods of plating
conductors onto linen paper in 1904. Arthur Berry in 1913 patented a print-and-etch method in the
UK, and in the United States Max Schoop obtained a patent[6] to flame-spray metal onto a board
through a patterned mask. Charles Ducas in 1925 patented a method of electroplating circuit
patterns.[7]
Predating the printed circuit invention, and similar in spirit, was John Sargrove's 1936–1947
Electronic Circuit Making Equipment (ECME) that sprayed metal onto a Bakelite plastic board. The
ECME could produce three radio boards per minute.
