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As with any professional activity, electronics uses a wide range of words, many in ways which differ from their use in Standard English. In this glossary, we have tried to provide definitions for most of the terms which relate to design, fabrication, assembly and test of printed circuit assemblies and systems, and associated environmental issues.
This list has been integrated and adapted from three main sources:
plus inputs from:
You are recommended to follow the links for further details. You may also enjoy the glossary from a book with the intriguing title Bebop to the Boolean Boogie (An Unconventional Guide to Electronics) which has been abstracted at http://www.maxmon.com/glossary.htm.
Please feel free to suggest or request definitions for additional terms by emailing email@example.com.
There are many other sources which you can use to extend your knowledge of the terms used. For example, the book Surface Mount Technology Terms and Concepts by Phil Zarrow and Debra Kopp published in 1997 by Butterworth-Heinemann (ISBN 0750698756), reviewed by Bob Willis at http://www.smartgroup.org/books/smttc.htm.
For equipment, the SMEMA standards also contain a treasure trove of definitions. These are available on the web at http://www.smema.org/smemastandards.htm.
The terms Printed Circuit Board (PCB) and Printed Wiring Board (PWB) both describe the same thing, a ‘substrate’ that serves both to mount and to interconnect electronic components. It is usually planar, but may be flexible or three-dimensional.
There is continuing debate as to which of these terms is the more correct. Certainly at low frequency, the claim that the board is pure interconnect – that is, provides the ‘wiring’ – and that the circuit comprises the interconnections and components together, has won sufficient backing for PWB to remain the preferred alternative for the British Standards Institution and IPC. However, at higher frequencies, the board itself tends to become a circuit component, so the distinction is less valid.
PCB, whilst less pedantically correct, was however the earlier of the terms, and is still the most commonly used throughout the UK industry. We have therefore decided to refer throughout our course material to Printed Circuit Board (PCB).
Unfortunately, the acronym PCB has adverse connotations for environmentalists – polychlorinated biphenyls are a group of non-degrading, biologically hazardous materials formerly used for transformer cooling, that have been banned world-wide since 1999. You should be aware therefore of potential misunderstanding in some circles if you use the term PCB. However, there are many in the design industry for whom PWB will be an alien term, so you need to stay flexible. Rest assured that, whichever term you choose to use in your assignments, both will be regarded as correct!
The assembled version of the board, complete with components, similarly has two equivalent names, ‘Printed Circuit Assembly’ and ‘Printed Wiring Assembly’. However, the former is much more common, and we justify its use in this module on the grounds that the assembly has now become a complete (and hopefully functioning!) electronic circuit.
Certain words within the list are potentially slightly confusing, because their meaning depends on their context. Specific confusion comes from words such as lead and routing/router, which are ‘heteronyms’. This means that they have two meanings which correspond to different pronunciations of the word.
For example, ‘lead in your pencil’ (pronounced ‘led’) looks exactly the same as ‘you can lead a horse to water’ (pronounced ‘leed’). In electronics, when lead is pronounced the first way, we are referring to the metallic element; when pronounced the second way, then lead means an individual connection to a component.
‘Routing’ is another heteronym – for the operation of creating wiring patterns, it is pronounced ‘rooting‘: pronounced ‘rowting‘, it refers to a mechanical operation involved in separating individual circuit boards from a larger panel. If you find this confusion, then follow the links!
Do spend a little time browsing this glossary: you may find other confusing words! For those of you with an interest in language, there is an excellent list of heteronyms at http://www-personal.umich.edu/~cellis/heteronym.html.
Other words are context-sensitive, that is their pronunciation is constant but their meaning depends on where the word is used. A particular case of this in electronic design and manufacture is the word ‘placement’. Used at an assembly stage, this means the process of collecting the right component and putting it in the appropriate place on the printed circuit board; at the design stage, however, placement refers to the distributing of components on the design, so that the ‘routing’ of the connections (and the physical location of the components) is optimised.
The PCB industry started in the 1950s at a time when the UK was using the Imperial System of measurements, and Americans still tend to think in terms of inches. For this reason, many of the common panel sizes are integral numbers of inches, and the older styles of component have lead spacings typically based on creating 10 or 20 connection opportunities per linear inch.
While the figures are nicely rounded within the inch context, their metric equivalents need more decimal places. You always need to be absolutely certain whether the part you are designing around has a basis in metric or imperial measurements, particularly where there are number of measurements whose dimensions add up. A particular danger is with connectors, where 0.100 inches (2.54mm) connectors co-exist with 2.5mm parts: they look very similar, and are indistinguishable to the naked eye, but fail to fit each other’s footprints after relatively few pins – the differences gradually add up!
CAD systems can always be adjusted to think either metric or imperial measure, but you should remain aware of the potential for error. Accompanying the general shrinking in board feature dimensions, there is fortunately a trend towards using the µm or micron as a basis for measurement, but mil/thou will be with us for some time to come.
Other differences between American and European practices concern units of weight (lbs and kg) and pressure (bar vs. psi). If you are faced with unfamiliar units, there is a useful conversion factor calculator at http://www.processassociates.com/process/convert/cf_all.htm.
You have to be careful when using prefixes for units, in particular to distinguish lowercase k (for kilo, the x1,000 multiplier) from uppercase K, which is used within computing circles to indicate 210, or 1024.
Similarly with lowercase m, which means milli (one-thousandth) and uppercase M which means Mega (multiply by one million). Even more confusingly, the micron sign (available in the extended ASCII set at Alt-0181) is often inserted as an m in Symbol font, and can sometimes revert to an m in the normal font, becoming 1,000 times bigger instantly! This is a case where knowledge of likely values is important.
kHz (for kilohertz) small ‘k’ (not KHz)
kg = kilogram (not Kg)
MHz for megahertz (not MHZ, Mhz, mhz)
Gb for gigabyte (not gb or GB)
SI prefixes In order to keep to a minimum the number of leading or trailing zeros, a number of prefixes have been defined which cover the range 1024 to 10−24. Most of these are quite well known, but a complete list is available at http://www.npl.co.uk/npl/reference/si_prefixes.html.
If you are interested in some of the issues relating to units, we recommend looking at the NPL Beginner’s Guides to Measurement at http://www.npl.co.uk/npl/publications/posters.html, which introduce important features and concepts on aspects of measurement.[ back to top ]
Author: Martin Tarr
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