PCB Glossary of Terms

Analog Circuit:

A circuit in which the output varies as a continuous function of the input, as contrasted with digital circuit.

Assembly Drawing:

A drawing depicting the locations of components, with their reference designators (q.v.), on a printed circuit.

Assembly House:

A manufacturing facility for attaching and soldering components to a printed circuit.

Board:

printed circuit board. Also, a CAD database which represents the layout of a printed circuit.

Board House:

Board vendor. A manufacturer of printed circuit boards.

Body:

The portion of an electronic component exclusive of its pins or leads.

CAD:

Computer Aided Design. A system where engineers create a design and see the proposed product in front of them on a graphics screen or in the form of a computer printout or plot. In electronics, the result would be a printed circuit layout.

CAE:

Computer Assisted Engineering. In electronics work, CAE refers to schematic software packages.

CAM:

Computer Aided Manufacturing. (See CAM files)

CAM Files:

CAM means Computer Aided Manufacturing. These are the data files used directly in the manufacture of printed wiring. The types of CAM files are 1) Gerber file, which controls a photoplotter, 2) NC Drill file, which controls an NC Drill machine and 3) fab and assembly drawings in soft form (pen-plotter files). CAM files represent the valuable final product of PCB design. They are handed off to the board house which further refines and manipulates CAM data in their processes, for example in step- and-repeat panelization. Some PCB design software companies refer to all plotter or printer files as CAM file, although some of the plots may be check plots which are not used in manufacture.

Card:

Another name for a printed circuit board.

Card-Edge Connector:

A connector which is fabricated as an integral portion of a printed circuit board along part of its edge. Often employed to enable a daughter or add-on card.

Capture:

Extract information automatically through the use of software, as opposed to hand-entering of data into a computer file.

Check Plots:

Pen plots that are suitable for checking only. Pads are represented as circles and thick traces as rectangular outlines instead of filled-in artwork. This technique is used to enhance transparency of multiple layers.

Chip on Board:

In this technology, integrated circuits are glued and wire-bonded directly to printed circuit boards instead of first being packaged. The electronics for many mass-produced toys are embedded by this system, which can be identified by the black glob of plastic sitting on the board. Underneath that glob (technical term: glob top ), is a chip with fine wires bonded to both it and the landing pads on the board.

Clad:

A copper object on a printed circuit board. Specifying certain text items for a board to be "in clad" means that the text should be made of copper, not silkscreen.

Component:

Any of the basic parts used in building electronic equipment, such as a resistor, capacitor, DIP or connector, etc.

Component Library:

A representation of components as decals, stored in a computer data file which can be accessed by a PCB CAD program.

Connection:

One leg of a net. Also called a "pin pair".

Connectivity:

The intelligence inherent in PCB CAD software which maintains the correct connections between pins of components as defined by the schematic.

Connector:

A plug or receptacle which can be easily joined to or separated from its mate. Multiple-contact connectors join two or more conductors with others in one mechanical assembly.

Decal:

A graphic software representation of a component, so named because hand tape-up of printed circuit boards employed the use of pull-off and paste decals to represent components. Also called a part, footprint or package. On a the manufactured board the body is an epoxy-ink outline.

Digital Circuit:

A circuit which operates like a switch (it is either "on" or "off"), and can make logical decisions. It is used in computers or similar decision making equipment.

DIP:

Abbreviation for dual in-line package. A type of housing for integrated circuits. The standard form is a molded plastic container of varying lengths and 0.3 inch wide, with two rows of pins space 0.1 inch between centers of adjacent pins.

Double-Track:

Slang for fine line design with two traces between DIP pins.

Dry Film Solder Mask:

A solder mask film applied to a printed board with photographic methods. This method can manage the higher resolution required for fine line design and surface mount. It is more expensive than liquid photoimageable solder mask.

Fab:

Short for fabrication.

Fabrication Drawing:

A drawing used to aid the construction of a printed board. It shows all of the locations of the holes to be drilled, their sizes and tolerances, dimensions of the board edges, and notes on the materials and methods to be used. Called "fab drawing" for short. It relates the board edge to at least on hole location as a reference point so that the NC Drill file can be properly lined up.

Fine Line Design:

Printed circuit design permitting two (rarely three) traces between adjacent dip pins. It entails the use of a either dry film solder mask or liquid photoimageable solder mask (LPI), both of which are more accurate than wet solder mask.

Fine Pitch:

Refers to chip packages with lead pitches below 0.050". The largest pitch in this class of parts is 0.8mm, or about 0.031". Lead pitches as small as 0.5mm (0.020") are used.

Finger:

A gold-plated terminal of a card-edge connector. [Derived from its shape.]

Footprint:

1. The pattern and space on a board taken up by a component.

2. Decal.

Gerber File:

Data file used to control a photoplotter. Named after Gerber Scientific Co., who made the original vector photoplotter.

Glob Top:

A blob of non-conductive plastic, often black in color, which protects the chip and wire bonds on a packaged IC and also on a chip on board . This specialized plastic has a low coefficient of thermal expansion so that ambient temperature changes will not rip loose the wire bonds it is designed to protect. In high-volume chip on board production, these are deposited by automated machinery and are round. In prototype work, they are deposited by hand and can be custom-shaped; however, in designing for manufacturability, one assumes a prototype product will "take- off" and ultimately have high market demand, and so lays out chip on board to accommodate a round glob top with adequate tolerance for machine-driven "slop-over".

Header:

The portion of a connector assemble which is mounted on a printed circuit.

IC:

Integrated Circuit.

IPC:

The Institute for Interconnecting and Packaging Electronic Circuits, the final American authority on how to design and manufacture printed wiring. In 1999, IPC changed its name from Institute of Interconnecting and Packaging Electronic Circuits to IPC. The new name is accompanied with an identity statement, Association Connecting Electronics Industries.

Laser Photoplotter:

(also "laser plotter") A photoplotter which simulates a vector photoplotter by using software to create a raster image of the individual objects in a CAD database, then plotting the image as a series of lines of dots at very fine resolution. A laser photoplotter is capable of more accurate and consistent plots than a vector photoplotter.

Lead:

(pronounced "leed") A terminal on a component.

Liquid Photoimageable Solder Mask (LPI):

A mask sprayed on using photographic imaging techniques to control deposition. It is the most accurate method of mask application and results in a thinner mask than dry film solder mask. It is often preferred for dense SMT.

LPI:

Stands for Liquid Photoimageable. Refers to liquid photoimageable solder mask.

Mil:

One thousandth of an inch.

Multimeter:

A portable test instrument which can be used to measure voltage, current, and resistance.

NC Drill:

Numeric Control drill machine. A machine used to drill the holes in a printed board at exact locations, which are specified in a data file.

Negative:

1. n. A reverse-image contact copy of a positive, useful for checking revisions of a PCB. If the negative of the current version is superimposed over a positive of an earlier version, all areas will be solid black except where changes have been made.

2. adj. (Of a PCB image) Representing copper (or other material) as clear areas and absence of material as black areas. Typical of power and ground planes and solder mask.

Node:

A pin or lead which will have at least one wire connected to it.

Open:

Open circuit. An unwanted break in the continuity of an electrical circuit which prevents current from flowing.

Package:

1. Decal or printed wiring board component.

2. A type of PCB component which contains a chip and acts to make a convenient mechanism for protecting the chip while on the shelf and after attachment to a PCB. With its leads soldered to a printed board, a package serves as the electrical conduction interface between the chip and the board. An example is a DIP.

Panel:

Material (most commonly an epoxy-copper laminate known as FR-4) sized for fabrication of printed circuit boards. The most common panel size is 12" by 18", of which 11" by 17" is available for printed circuitry.

Panelize:

1. To lay up more than one (usually identical)printed circuits on a pans. Individual printed circuits on a panel need a margin between them of 0.3". Some board houses permit less separation.

2. Lay up multiple printed circuits (called modules) into a sub-panel so that the sub-panel can be assembled as a unit. The modules can then be separated after assembly into discrete printed circuits.

Part:

1. Component.

2. A decal in a PWB database or drawing. 3. A symbol in a schematic.

PCB:

Printed circuit board.

PCB Database:

All of the data fundamental to a PCB design, stored as one or more files on a computer.

Photoplotter:

Device used to generate artwork photographically by plotting objects (as opposed to copying an entire image at once as with a camera) onto film for use in manufacturing printed wiring.

Pin:

A terminal on a component, whether SMT or through-hole. [Derived from its physical shape on through-hole components, which predated SMT.] Also called lead.

Plated-Through Hole:

A hole in a PWB with metal plating added after it is drilled. Its purpose it to serve either as a contact point for a through-hole component or as a via.

Plastic Leaded Chip Carrier:

An SMT chip package that is rectangular or square- shaped with leads on all four sides. The leads are spaced at 0.050 inches, so this package is not considered fine-pitch.

Positive:

1. n. A developed image of photoplotted film, where the areas selectively exposed by the photo plotter appear black, and unexposed areas are clear. Board houses work from positives, and a photo plotter produces positives, thus one set of positives is all the film that is needed to produce a printed wiring board.

2. adj. (of a printed wiring image) Representing copper as black areas and absence of copper as clear areas. Typical of images of routed layers of a PWB.

Printed Circuit Board:

A flat plate or base of insulating material containing a pattern of conducting material. It becomes an electrical circuit when components are attached and soldered to it.

The conducting material is commonly copper which has been coated with solder or plated with tin or tin-lead alloy. The usual insulating material is epoxy laminate. But there are many other kinds of materials used in more exotic technologies.

Single-sided boards, the most common style in mass-produced consumer electronic products, have all conductors on one side of the board. With two-sided boards, the conductors, or copper traces, can travel from one side of the board to the other through plated-thru holes called vias, or feed-throughs. In multilayer boards, the vias can connect to internal layers as well as either side.

PWB:

Printed Wiring Board; same as PCB.

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 description like "PQFP-160" is inadequate to define the mechanical size and lead pitch of the part.

Rats nest:

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 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.

Route:

1. n. A layout or wiring of a connection.

2. v. The action of creating such a wiring.

Schematic:

A diagram which shows, by means of graphic symbols, the electrical connections and functions of a specific circuit arrangement.

Short:

Short circuit. 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.

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. The silk mesh size commonly used is 6 mils. Thus, 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.

2. A Gerber file controlling the photoplotting of this legend.

Single Track:

PCB design with only one route between adjacent DIP pins.

SMD:

Surface Mount Device.

SMT:

Surface Mount Technology.

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.

Stuff:

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.

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.

Terminal:

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

Test Coupon:

An area of patterns on the same fabrication panel as the PWB, but separate from the electrical circuits and outside the actual board outline. It is cut away from the printed wiring board prior to assembly and soldering of components. It can be used for destructive testing.

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. Contrast with surface mount.

Thru-Hole:

Same as through-hole.

Trace:

Segment of a route.

Track:

Trace.

UL:

Underwriter's Laboratories, Inc., a corporation supported by some underwriters for the purpose of establishing safety standards on types of equipment or components.

Vector Photoplotter:

(also "Vector Plotter", or "Gerber Photoplotter" after Gerber Scientific Co., which built the first vector photoplotters for commercial use) It plots 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 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. The apertures are mounted on an "aperture wheel" which can hold up to 24 apertures. Gerber photoplotters, if set up by an experienced craftsman, are well-suited for printed circuit artwork generation. Compare with laser photoplotter , which is faster and has largely replaced the vector photoplotter. There are still vector photoplotters in use. Some 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.

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.

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 accurate 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.

Wire Wrap Area:

A portion of a board riddled with plated-through holes on a 100-mil grid. Its purpose is for accepting circuits which may be found necessary after a PWB has been manufactured, stuffed, tested and debugged.