Typically, the chassis was a sheet metal frame or pan, sometimes with a wooden bottom. History Predecessors Īn example of hand-drawn etched traces on a PCBīefore the development of printed circuit boards, electrical and electronic circuits were wired point-to-point on a chassis. The world market for bare PCBs exceeded $60.2 billion in 2014 and is estimated to reach $79 billion by 2024. However, multilayer PCBs make repair, analysis, and field modification of circuits much more difficult and usually impractical. 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. Multi-layer PCBs allow for much higher component density, because circuit traces on the inner layers would otherwise take up surface space between components. 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). PCBs can also be made manually in small quantities, with reduced benefits. Large numbers of PCBs can be fabricated at the same time, and the layout has to be done only once. Mass-producing circuits with PCBs is cheaper and faster than with other wiring methods, as components are mounted and wired in one operation.
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Electronic design automation software is available to do much of the work of layout. PCBs require additional design effort to lay out the circuit, but manufacturing and assembly can be automated. Alternatives to PCBs include wire wrap and point-to-point construction, both once popular but now rarely used. Printed circuit boards are used in nearly all electronic products. Another manufacturing process adds vias: plated-through holes that allow interconnections between layers.
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. 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. 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 mountingĪ printed circuit board ( PCB also printed wiring board or PWB) is a medium used to connect electronic components to one another in a controlled manner.
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