printed circuit

An electric circuit in which the conducting connections have been printed or otherwise deposited in predetermined patterns on an insulating base.

A conductive pattern that may or may not include printed components, formed in a predetermined design on the surface of an insulating base in an accurately repeatable manner. Printed circuits are fabricated by any of several graphic art processes. They greatly simplify mass production and increase equipment reliability. Their most important contribution, however, is the tremendous reduction achieved in size and weight of electronic devices and equipment. Printed circuits are used in practically all types of electronic equipment: toys, radio and television sets, telephone systems units, electrical wiring behind automobile dashboards, computers, and industrial control equipment.

Technology

The configuration in which electronic circuit elements are located and the routing of conductor paths between the circuit elements establish the precise circuit pattern. Location of the circuit elements can depend on a number of factors, including the form factor (outline of a printed wiring board in a piece of electronic equipment), signal criticality, and the power dissipation of the circuit elements. Conductor path routing is a function of the circuit element location, signal criticality, width and spacing of interconnection conductors, number of wiring channels per layer of interconnect structure, and number of interconnect layers allowed.

As a result of increased circuit complexity, sophisticated computer-aided engineering (CAE) programs have been developed to automate the design of printed circuits. Output from the computer-aided engineering database includes a circuit element parts list and schematic diagrams of the circuit interconnections. This computer-aided engineering database can be used as input to a computer-aided design (CAD) program that optimizes the location of circuit elements within the given form factor and automatically performs the conductor routing between circuit elements. See also Computer-aided design and manufacturing; Computer-aided engineering.

Artwork masters are used to fabricate the screens and masks for the application of photoresistive materials in the actual formation of the required patterns on the finished parts. The computer-aided design database is also used in the preparation of numerous types of tooling, for example, drill templates, tapes for operation of numerical-tape-controlled drilling equipment, routing templates and dicing fixtures for trimming printed circuits or integrated-circuit dies to final configuration, laminating and holding fixtures, and string lists to drive automated test equipment. Numerous processes, including etching, screening, plating, laminating, vacuum deposition, diffusion, and application of protective coatings, are used in combination to produce various types of printed circuits. Completed printed circuits are inspected visually and dimensionally by using such techniques as microsectioning and infrared photospectrometer measurements in determining thicknesses of critical materials; in addition, they may be x-rayed and electrically tested to assure conformance to requirements. See also Printing.

Printed wiring

Printed wiring is undoubtedly the most common type of printed circuit. The printed wiring board (PWB) is a copper-clad dielectric material with conductors etched on the external or internal layers. Printed wiring boards can be subdivided into single-sided, double-sided, and multilayer boards.

Single-sided boards contain all the interconnect structure on one of the external layers and are the least expensive to manufacture. Double-sided boards contain circuitry on both external layers. Plated through-holes and occasionally eyelets are used to provide electrical continuity between the sides. Double-sided boards are used in those applications in which the maximum number of interconnections (conductors) in a given area are required for minimum cost. Both single- and double-sided boards are commonly used in such commercial applications as automotive equipment, radio and television sets, and toys.

Multilayer boards contain circuitry on internal layers throughout the cross section of the board as well as on the external layers. Because of the reduced size of miniaturized microelectronic parts, these boards accommodate the increasing complexity and density of circuitry used in applications such as high-speed computers and signal processors. Multilayer printed wiring boards are manufactured by using two different methods: subtractive (print and etch) technology and additive (plate-up) technology.

Thick-film circuits

Thick-film circuits consist of such passive elements as resistors, capacitors, and inductors deposited on wafers or substrates of such dielectric materials as ceramic, glass, quartz, sapphire, and porcelain-coated metal. They are used for mass fabrication of passive networks for inclusion in linear microcircuits and large-signal digital and analog modules. Thick-film design and manufacture are usually based on film thicknesses of approximately 0.0005–0.0015 in. (12–38 μm).

Thin-film circuits

The deposition of thin films was the first application of printed circuit technology to microelectronics. The most important advantages to thin-film circuits are the following: (1) films with a uniform thickness in the range from 5 × 10⁻⁶ mm to 5 × 10⁻³ mm can be vacuum-deposited and controlled by measuring the resistance across a test pattern during deposition to ensure that final thicknesses are within design limits; (2) patterns formed during deposition or by selective etching afterward are much more precisely controlled than those which are printed, as in thick-film circuits; (3) more stable resistive materials can be used; and (4) thin films have less porous surface metallization, enabling faster rise times. Because of this precision and stability, thin-film circuits are frequently used in radio-frequency applications in avionics and industrial electronics.

Multichip devices

A multichip device, often referred to as a hybrid, is a combination of two or more electronic components mounted and interconnected via a substrate. The multichip device serves a customized electronic function and is packaged as a single device.

A multichip device serves the same function as a circuit card assembly; however, all the components are packaged together in a single hermetic case. Unlike printed wiring boards where all components are individually packaged and then mounted to the board, multichip devices may use bare, unpackaged dies. The advantages of multichip devices are the vast reduction in volume, area, and weight; improved thermal management; and increased functional densities, frequencies, and electrical performance. The disadvantage is the increased cost over that of equivalent printed wiring board assemblies. Multichip devices can be digital, analog, or a combination of both.

The interconnection of transistors and other electronic components via pathways made of copper or some other conductive material that is etched or laminated onto a rigid or flexible surface. The "printed" means that the material is deposited onto the substrate and that discrete wires are not used. The printed circuit stems back to the 1940s. See printed circuit board.

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For more information on printed circuit, visit Britannica.com.

Printed circuit may refer to:

• Printed circuit board
• Printed Circuit, a synthpop artist
• Printed Circuit Corporation, an electronics manufacturer

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