Glossary of PCB from Q-Z

QFP —Quad Flat Pack, a fine-pitch SMT package that is rectangular or square with gull-wing shaped leads on all four sides. The lead pitch of a QFP is typically either 0.8mm or 0.65mm, although there are variations on this theme with smaller lead pitches: TQFP also 0.8mm; PQFP tooled at either 0.65mm (0.026") or 0.025" and SQFP at 0.5mm (0.020"). Any of these packages can have a wide variety of lead counts from 44 leads on up to 240 or more. Although these terms are descriptive, there are no industry- wide standards for sizes. Any printed circuit designer will need a spec sheet for the particular manufacturer's part, as a brief descrition like "PQFP-160" is inadequate to define the mechanical size and lead pitch of the part.

  

Ratsnest —A bunch of straight lines (unrouted connections) between pins which represents graphically the connectivity of a PCB CAD database. [Derived from the pattern of the lines: as they crisscross the board, the lines form a seemingly haphazard and confusing mess similar to a rat 's nest.)

Reference designator (abbrv. "ref des")—The name of a component on a printed circuit by convention beginning with one or two letters followed by a numeric value. The letter designates the class of component; eg. "Q" is commonly used as a prefix for transistors. Reference designators appear as usually white or yellow epoxy ink (the "silkscreen") on a circuit board. They are placed close to their respective components but not underneath them, so that they are visible on the assembled board. By contrast, on an assembly drawing a reference designator is often placed within the boundaries of a footprint--a very useful technique for eliminating ambiguity on a crowded board where reference designators in the silkscreeen may be near more than one component.

RF —Radio Frequency.

Rise time —the time required for an output voltage of a digital cirucit to change from low voltage level (0) to high voltage leve (1), after the change has started. Very short rise times, not high clock speeds, are the primary cause of cross-talk in PCBs. Rise times are charactericstic of the technology being used in a circuit. Gallium Arsenide components can have rise times around 100-picoseconds (millionths of millionths of seconds), 30 to 50 times faster than some CMOS components.

Route —1. n. A layout or wiring of a connection. 2. v. The action of creating such a wiring.

   

Saturation —1.  The operating condition of a transistor when an increase in base current produces no further increase in collector current.  2.  A circuit condition whereby an increase in the driving or input signal no longer produces a change in the output.  3.  The condition when a transistor is driven so hard that it becomes biased in the forward direction. In a switching application, the charge stored in the base region prevents the transistor from turning off quickly under saturation conditions.  4.  Generally, that state in which a semiconductor device is conducting most heavily for a given applied voltage. In many devices it is also a state in which the normal amplification mechanisms have become "swamped" and inoperative. 

Schematic —A diagram which shows, by means of graphic symbols, the electrical connections, components and functions of an electrical system. The components are represented by agreed-upon symbols, and the conductors connecting them by lines. If two lines cross each other, a large dot represents a junction, whereas no dot represents no connection.

Short —Short circuit. 1. An abnormal connection of relatively low resistance between two points of a circuit. The result is excess (often damaging) current between these points. Such a connection is considered to have occurred in a printed wiring CAD database or artwork anytime conductors from different nets either touch or come closer than the minimum spacing allowed for the design rules being use.

Signal —1. A net. 2. A net other than a power or ground net.

Silicon wafer —a thin, iridescent, silvery disk of silicon which contains a set of integrated circuits, prior to their being cut free and packaged. A silicon wafer will diffract reflected light into rainbow patterns and, being a similar size, looks so much like a music CD that it could be mistaken for one (except that it has no label or hole in the middle). On closer inspection, one can see the individual (usually rectangular- or square-shaped) integrated circuits which form a uniform patchwork quite unlike the surface of a music CD. When cut or etched from the wafer these circuits are then called chips or dice.

Silkscreen —(Also called "silkscreen legend") 1. The decals and reference designators in epoxy ink on a printed wiring board, so called because of the method of application—the ink is "squeegeed" through a silk screen, the same technique used in the printing of T-shirts.

A silk mesh size commonly used is 6 mils. With this mesh size, the absolute minimum line width of any silkscreen legend artwork is 6 mils, which leaves a very faint line. 7 mils works better for a practical minimum line width.

Newer silkscreening methods allow for sikscreen draws of 5 mils, which come out very clear. A good reference designator size to use is 35 mils high with a 5 mil draw

Single track —PCB design with only one route between adjacent DIP pins.

SMD —1.  Surface Mount Device (SMT component).  2.  Solder-Mask Defined

SMT —Surface Mount Technology.

Soft —Pertaining to or consisting of software.

Soft copy —An electronic form of a document; a data file in computer memory or stored on storage media. When one is looking at a soft copy he is viewing the document as displayed on a computer monitor.

Solder mask —A technique wherein everything on a circuit board is coated with a plastic except 1) the contacts to be soldered, 2) the gold-plated terminals of any card-edge connectors and 3)fiducial marks.

SQFP —Shrink Quad Flat Pack.

Stable datum —a datum along which all other data align. From any confusion, order and sanity can emerge providing one merely selects a datum, assigns it importance or seniority and then begins to align other data against it. 

The stable datum for any PCB layout could be stated this way:  The schematic is the "Bible." In other word, the schematic says the circuit is this way, and the PCB design must follow that pattern perfectly.

Stuff —Slang Populate. Attach and solder components to (a printed wiring board).

Sub-panel —A group of printed circuits (called modules) arrayed in a panel and handled by both the board house and the assembly house as though it were a single printed wiring board. The sub-panel is usually prepared at the board house by routing most of the material separating individual modules, leaving small tabs. The tabs are strong enough so that the sub-panel can be assembled as a unit, and weak enough so that final separation of assembled modules is easily done.

Substrate —The supporting material on or in which the parts of an integrated circuit are attached or made. The substrate may be passive ( thin film, hybrid) or active ( monolithic compatible).

Surface mount —Surface mount technology. The technology of creating printed wiring wherein components are soldered to the board without using holes. The result is higher component density, allowing smaller PWB 's. Abbreviated SMT.

Symbol —A simplified design representing a part in a schematic circuit diagram.

TAB —Tape Automated Bonding.

Tented via —a via with dry film solder mask completely covering both its pad and its plated-thru hole. This completely insulates the via from foreign objects, thus protecting against accidental shorts, but it also renders the via unusable as a test point. Sometimes vias are tented on the top side of the board and left uncovered on the bottom side to permit probing from that side only with a test fixture.

TDR —Time Domain Reflectometer, a device which a board house can use for measuring characteristic impedance of a conductor on a printed board, thus insuring an accurate build for controlled impedance.

Terminal —A point of connection for two or more conductors in an electrical circuit; one of the conductors is usually an electrical contact, lead or electrode of a component.

Terminal block —a type of header to which wires are attached directly instead of by means of a connector plug. Each wire is inserted in a hole in the terminal block , and then anchored by means of a screw.

Test coupon —An area of patterns and holes located on the same fabrication panel as the actual PCB, but separate from the electrical circuits and outside the board outline(s). It is designed to reflect the technology used on the PCB, such as smallest plated-through hole size, any blind or buried vias, etc. It is cut away from the panel and can be embedded in a clear plastic to prepare it for destructive testing.

Thin film —A film of conductive or insulating material, usually deposited by sputtering or evaporation, that may be made in a pattern to form electronic components and conductors on a substrate or used as insulation between successive layers of components.

   

Through-hole — (Of a component, also spelled "thru-hole"). Having pins designed to be inserted into holes and soldered to pads on a printed board.

TQFP —Thin Quad Flat Pack. Essentially the same as a QFP except low-profile, that is, thinner.

Trace —Segment of a route

Track — Trace.

US-ASCII —The 7-bit (using character codes 0-127) version of ASCII, which preceded (and is the basis for) 8-bit versions such as Latin-1, MacASCII and later, even larger coded character sets such as Unicode.

Valuable Final Artwork —A term used in " Streamedline PCB Design". Artwork for electronic circuits which have been laid out and documented in forms perfectly suited to the photo-imaging and numeric-controlled tooling processes of printed circuit manufacture. It is termed "final" because it has been thoroughly checked for errors and any corrected as needed and is now ready for manufacture without further work by the PCB designer. It is valuable because it could be exchanged with a customer for money or other support.

Valuable Final Product — Something that can be exchanged with other activities in return for support. The support usually adds up to food, clothing, shelter, money, tolerance and cooperation (goodwill).... A valuable final product (VFP) is valuable because it is potentially or factually exchangeable. The key word in this sense is EXCHANGEABLE. And exchangeability means outside, with something outside the person or activity. A valuable final product could as easily be named a VALUABLE EXCHANGEABLE PRODUCT. [L. Ron Hubbard, March 25, 1971, "Valuable Final Products."]

vcc or VCC or Vcc —A name for a power net meaning "voltage collector," usually +5V for TTL circuits.

vdd or VDD or Vdd —A name for a power net meaning "voltage drain," usually implying a more positive voltage.

Vector photoplotter —(also "vector plotter", or "Gerber photoplotter" after Gerber Scientific Co., which built the first vector photoplotters for commercial use)  It plots images from a CAD database on photographic film in a darkroom by drawing each line with a continuous lamp shined through an annular-ring aperture, and creating each shape (or pad) by flashing the lamp through a specially sized and shaped aperture. The "apertures" are thin trapezoidal pieces of plastic which are mostly opaque, but with a transparent portion that controls the size and shape of the light pattern passing through it. The apertures are mounted on an " aperture wheel" which can hold up to 24 apertures (or 70 on certain models). The lamp and aperture wheel are fixed, and the table holding the film is moved in x and y dimensions (on small photoplotters), or vice versa (on very large photoplotters). A numeric datum sent to the control circuit of the photoplotter is either a D code or an X and/or Y dimension in inches, to the nearest thousandth. If it is a D code equal to D10 or above, the message tells the wheel to rotate the corresponding aperture location into position in front of the lamp. .  Gerber photoplotters, if set up by an experienced craftsman, are well-suited for printed circuit artwork generation. Compare with laser photoplotter, which is faster, more accurate and has largely replaced the vector photoplotter.

e manufacturers take advantage of the large bed size of the largest Gerber photoplotters, roughly the size of a full-sized billiards table. This enables the production of very large photoplots. An example is Buckbee-Mears, which makes large antenna boards, and the USGS (United States Geological Survey) which has used them in map-making.

vee or VEE or Vee —A name for a power net meaning "voltage emitter," usually -5V for ECL circuits.

Via —Feed-through. A plated-through hole in a PWB used to route a trace vertically in the board, that is, from one layer to another.

VLSI —Very Large Scale Integration.

VQFP —Very thin Quad Flat Pack.

vss or VSS or Vss —A name for a power net meaning "voltage source," usually implying a more negative voltage and often equivalent to Ground or GND.

Wet solder mask —Applied by means of distributing wet epoxy ink through a silk screen, a wet solder mask has a resolution suitable for single-track design, but is not accruate enough for fine-line design.

Wire —Besides its usual definition of a strand of conductor, wire on a printed board also means a route or track.

In this article I have tried to explain few important words related to PCB starts from Q-Z...

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Ruby