 | This page is a candidate to be copied to Wikibooks using the Import process.
If the page can be re-written into an encyclopedic article, please do so and remove this message.
Before you move this content to Wikibooks, verify that it conforms to Wikibooks policies of acceptable content at What is Wikibooks?. Often content unacceptable to Wikipedia may not be acceptable on Wikibooks either; facilitate the copying of this article by listing it on Wikibooks:Requests for Import. Image File history File links Edit-copy. ...
Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is a wiki for the creation of books. ...
| Usually an electronics or electrical engineer designs the circuit, and a layout specialist designs the PCB. PCB design is a specialized skill. There are numerous techniques and standards used to design a PCB that is easy to manufacture and yet small and inexpensive. Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...
Most PCBs have between one and twenty conductive layers laminated (glued) together in a sandwich with insulating plastic. PCBs with more than two layers help construct complex or dense circuits. They are not always used because they are more expensive, and the inner layers are more difficult to inspect and repair.
In more complex PCBs, two or more of the layers are dedicated to providing ground and power. These ground planes and power planes distribute power well. They also prevent radio waves from antennas unintentionally formed by tracks. These planes are rectangular sheets of foil that occupy entire layers (except for small holes to avoid unwanted connection to vias and through-hole components). They distribute electrical power and heat better than narrow traces. Sometimes solid metal PCBs with thin layers of insulation are used. The power electronic substrate carries away waste heat when air cooling is impossible. In telecommunication, a ground plane is an electrically conductive surface that serves as the near-field reflection point for an antenna, or as a reference ground in a circuit. ...
See ground plane. ...
The role of the substrates in Power electronics is twofold: to provide the interconnections to form an electric circuit (like a Printed Circuit Board), and a convenient way to cool the components. ...
Four-layer PCBs with a ground and power plane are often used in high-quality, but cost-conscious audio, avionics and medical electronics. Most consumer products have one or two layers.
The width and spacing of conductors (or "traces") on a PCB is very important. If the traces are too close, solder can short adjacent traces, and the PCB will be difficult to construct or repair. If too far apart, the PCB may be too large and expensive. When a PCB carries high frequencies, traces may need to be exact widths and lengths to control the characteristic impedance of the trace. The characteristic impedance of a uniform transmission line is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. ...
Some designs cut the ground plane or the entire PCB in strategic locations to control the return paths of currents. The usual desire is to keep high voltages or frequencies away from sensitive portions of a circuit. The actual properties of the design are critical, because in some cases, cutting the ground plane makes the PCB into an antenna that radiates radio noise into nearby equipment.
Removing large areas of copper wastes etchant and increases pollution. Also, a PCB etches more consistently and tends to resist warping if all regions have the same average ratio of copper to bare board. Therefore, designers may widen connectors, leave unconnected copper in place, or cover large areas of what would otherwise be bare board with arrays of small, electrically isolated copper diamonds or squares.
Most PCBs have alignment marks (called fiducials) and tooling holes to align layers. These permit the PCB to be mounted in equipment that automatically places and solders components. Some designs also have quality control patterns to measure soldering and etching processes. In some cases, the test patterns are on break-off tabs that can be removed before the PCB is installed. In statistics, fiducial inference is a form of interval estimation developed by Ronald Fisher in connection with the Behrens-Fisher problem. ...
Layers may be connected together through drilled holes called vias. Either the holes are electroplated or small rivets are inserted. High-density PCBs may have blind vias, which are visible only on one surface, or buried vias, which are visible on neither, but these are expensive to build and difficult or impossible to inspect after manufacture. Good designers minimize the number of vias to reduce the cost of drilling. On older, two-layer PCBs, it was common to solder a wire through the hole.
A solder mask is a plastic layer that resists wetting by solder (the solder is said to "bead up"), and keeps islands of solder from running together. It also protects the outside conductors layers from abrasion and corrosion. Without the solder mask, the fiberglass-reinforced epoxy appears a translucent off-white. Solder masks are usually green, but they may be found in other colors. Epoxy or polyepoxide is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in the United...
A silkscreen legend on the top or bottom surface of the board provides readable information about component part numbers and placement. This aids in manufacturing and repair. To aid manual construction and repair, diodes, capacitors and integrated circuits are sometimes oriented in the same direction. Screen-printing, also known as silkscreening or serigraphy, is a printmaking technique that creates a sharp-edged single-color image using a stencil and a porous fabric. ...
New technology allows for the component designators to be printed directly onto the board surface, saving time and money by doing away with silkscreens. This is sometimes done by a special inkjet printer. A similar process has experimentally produced solder masks. Inkjet printers are a type of computer printer that operates by propelling tiny droplets of liquid ink onto paper. ...
Radio transmitters and radio receivers are difficult to design. PCB designers working on them must minimize parasitic effects due to layout of components, or take them into account with a general model and use simulation software such as SPICE. Screen shot of Spice OPUS, a fork of Berkeley SPICE SPICE (Simulation Program with Integrated Circuits Emphasis) is a general purpose analog circuit simulator. ...
Fortunately, many practical circuits can be laid out using a much simpler lumped element model. An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ...
The lumped element model of electronic circuits makes the simplifying assumption that each element is an infinitesimal point in space, and that the wires connecting elements are perfect conductors. ...
PCB layout Basic guidelines: Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...
- it is often a good idea to have made a prototype circuit using point-to-point construction or wire wrap, as you will have solved certain basic issues to do with component selection: (eg: should I use a 1/4 watt resistor here, or do I need 1/2 watt? etc.)
- consider physical constraints on the assembled board's size and heat dissipation requirements; choose your heat sinks if needed.
- consider carefully the physical size of the components you are laying out; the circuit schematic doesn't tell you this. Equivalent components often have different packages.
- How do the components attach to the board? Are they surface mount components? or do they require holes, screws, washers, etc?
- are there mechanical parts directly mounted to the board? eg: switches or variable resistors?
- How will the board mount in its container? What stresses (shock, strain, shear) will there be upon it and upon components?
- How will the board connect to its power source? What other connectors will be required (e.g: signal inputs, outputs)?
- use construction paper and a pencil and sketch the board in its actual size; or use component layout software that includes information about the component outlines.
- decide appropriate widths for each of the signal traces; this depends on the current each trace is expected to carry.
- decide whether you will have a single-layer board, 2-layer, or multi-layer based on the circuit complexity and fabrication costs.
- begin by placing component outlines, then by placing signal traces; leave a little room around each for tolerances.
- for a single layer board, spend more effort to avoid having traces cross each other; play with component placement or run traces underneath components; sometimes a jumper wire is needed.
- in 2-layer and multilayer boards simply run the traces on different layers, and use plated-through holes to jump from one layer to another.
- try to predict and avoid assembly errors: where there are multiple components of the same kind, or where pins have a polarity (eg: electrolytic capacitors), try to place them in parallel and orient the positive pin in the same direction.
- If your PWB design software has a DRC (design rule check), use it.
PCB layout guidelines for RF circuits on a 2-layer or multilayer board: Point-to-point construction is the way most electronics were constructed before the 1950s. ...
This article deals with electronics manufacturing and prototyping techniques, see Wire wrap jewellery for the jewellery related topic Wire wrap is a technique for constructing small numbers of complex electronics. ...
The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ...
big massive knobs ...
This article or section does not cite its references or sources. ...
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ...
A schematic of the Washington Metro. ...
Surface-mount components on a keydrives circuit board Surface mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards (PCBs). ...
Electrical switches. ...
An ideal resistor is a component with an electrical resistance that remains constant regardless of the applied voltage or current flowing through the device. ...
In mechanics, a shock is a sudden acceleration or deceleration caused, for example, by impact or explosion. ...
Look up strain in Wiktionary, the free dictionary. ...
In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ...
On a printed circuit board, a signal trace is the printed circuit equivalent of a wire for carrying electrical signals. ...
In electricity, current refers to electric current, which is the flow of electric charge. ...
The polarity of an object is, in general, its physical alignment of atoms. ...
Electrolytic capacitors An electrolytic capacitor is a type of capacitor with a larger capacitance per unit volume than other types, making them valuable in relatively high-current and low-frequency electrical circuits. ...
Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...
Rough plot of Earths atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. ...
- identify the critical parts of the circuit and lay them out first
- have one of the layers act as a continuous ground plane (usually the 'bottom' side).
- if signal traces are constant width and height above the ground plane, and are properly terminated, then their characteristic impedance is more well-behaved and may be calculated.
- avoid sharp corners.
- keep signal traces and component leads as short as possible.
- inputs and outputs should be far apart, so that RF energy will not leak back from output to input. stages should line up, rather than snake around.
- decouple the RF parts of the circuit from the DC parts of the circuit.
- shield AF and IF components from RF components.
In telecommunication, a ground plane is an electrically conductive surface that serves as the near-field reflection point for an antenna, or as a reference ground in a circuit. ...
On a printed circuit board, a signal trace is the printed circuit equivalent of a wire for carrying electrical signals. ...
Electrical termination of a signal ceases its energy flow through the electrical circuit. ...
The characteristic impedance of a uniform transmission line is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. ...
On a printed circuit board, a signal trace is the printed circuit equivalent of a wire for carrying electrical signals. ...
Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...
An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies that is audible to humans. ...
An intermediate frequency (IF) is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. ...
See also
Schematic capture or schematic entry is a step in the design cycle of electronic design automation at which the electronic diagram, or schematic of the designed electronic circuit is created by a designer. ...
The field of electronics comprises the study and use of systems that operate by controlling the flow of electrons (or other charge carriers) in devices such as thermionic valves (vacuum tubes) and semiconductors. ...
This article presents a typical manufacturing process of an electronic assembly. ...
Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. ...
The process of circuit design can cover systems ranging from national power grids all the way down to the individual transistors within an integrated circuit. ...
External links
Manufacturer design tips Generally every PCB manufacturer gives some design for manufacturing tips on how to design things to fit their particular manufacturing process, for example Design for manufacturability (DFM) refers to the general engineering art of designing products in such a way that they are easy to manufacture. ...
Other external links - public component library for expresspcb
|
Feeds |
Contact