A-stage The stage of curing of a polymer resin where the polymer is still of relatively low molecular weight and thus both readily soluble and fusible.

A/D converter A functional circuit element or component that converts analogue signals to digital signals.

above-board profile The height that a component such as a connector stands above the top surface of the PCB

acceptance tests A set of tests performed to determine the acceptability of a PCB.

access time Time interval between the instant that a piece of information is sent to the memory device and the instant it returns .

activator One or more ingredients in a flux that create a wettable surface for solder, by removing oxides and possibly other contaminants when coming into contact with the metal on the parts to be soldered. These ingredients may or may not be corrosive at room temperature, but certainly must be active at elevated temperatures in order to perform their job properly. Activators are typically organic solids and organo-halides.

active component An electronic component whose parametric characteristics change while operating on an applied signal.

additive process A process for fabricating a printed circuit board by selectively depositing conductive material to define a conductor pattern on unclad, chemically treated laminate material.

adhesive characteristics Adhesive and cohesive strength over its expected operational environment are the essential characteristics of an adhesive material. Adhesion is the strength of the bond at the interface surface (see bond strength); cohesion is the bulk (cross-sectional) strength of the adhesive material.

adhesive dam A method of controlling the flow of adhesive material on inner layers of a multi layer board during lamination by providing an etched border of copper around the outer edges of the conductor layers.

Ag Chemical symbol for silver.

aging Mechanisms that cause degradation of properties or performance over a period of time.

alloy Mixture of two or more metals (see binary alloy; ternary alloy)

ambient Literally = ‘surrounding’, but usually interpreted as ‘room temperature’.

analogue (circuit) (USA ‘analog’) A type of circuit that deals with continuously varying voltage or current values that represent physical quantities, and where the output varies as a continuous function of the input, as contrasted with a digital circuit.

angle of attack The angle between the squeegee face and the stencil plane.

anisotropic conductive adhesive (ACA) An adhesive material that will conduct current only through its thickness (the so-called ‘Z-axis’). Usually made by filling a resin matrix with long, thin particles aligned with the Z-axis. Useful for making connections between circuit patterns on opposing substrates without shorting out adjacent pads. (Also called Z-axis adhesive.) Contrast isotropic conductive adhesive.

annular ring The portion of PWB conductor material (with through-hole designs, usually a pad) that completely surrounds a hole.

ANSI = American National Standards Institute An organization that establishes US and international standards. ANSI publications that are most applicable to printed circuits are those that define drafting procedures and documentation formats.

antioxidant As used when referring to fluxes, an antioxidant is a material that prevents re-oxidation of the metal surfaces after the activator has prepared them for soldering. Often, another material such as the vehicle might also serve as an antioxidant.

anti-wicking contacts Contacts on components such as connectors or switches that prevent entry of either flux or solder up into the contacts during the process that solders the contacts to the PCB.

aperture A predetermined shape (round, square, oblong, etc.), size (width, diameter), and type (draw or flash) that is exposed on artwork film by a photoplotter.

aperture library A collection of standard aperture descriptions.

aperture wheel Contains a set of individual physical apertures (or software definitions of apertures) that are specific for plotting a type or family of circuit board artworks.

aqueous cleaning A generic cleaning approach that uses water in combination with neutralizers, saponifiers and surfactants.

archiving data The process of relocating all the design and data files required to produce an end product into a retrievable storage area.

array A group of components arranged in rows and columns.

artwork (master) A photoprocessing tool used to fabricate a printed circuit board that consists of an accurately scaled image of the required pattern on the surface of a stable transparent film base.

Confusingly, as well as describing the photoplotted film, the term ‘artwork’ may refer just to the Gerber files used to drive the photoplotter, but is also often used to include other documentation used by a board house to manufacture a bare printed circuit board such as the NC drill file. See master artwork set.

The artwork description should include specifications for quality and orientation which will affect subsequent photoprocessing operations and/or usability .

ASCII format (ASCII code) Originally code which represents characters by numbers so that text can easily be transferred from one computer to another. The basic set covers only the numbers 0 to 127, of which the The ASCII character set is restrictive, and there are few variant ‘extended’ sets.

ASIC =Application-Specific Integrated Circuit An integrated circuit that is custom designed for a particular application. ASICs may be designed by interconnecting existing circuit sub-circuits (functional circuit building blocks that already exist in a library) or by developing and connecting a completely new set of circuit functions.

aspect ratio The ratio of the length or depth of a hole to its preplated diameter. Often used for the ratio of the thickness of the board to the diameter of its smallest via hole. Holes with high aspect ratios are difficult both to drill and plate and may be susceptible to cracking.

assembly A number of parts or subassemblies or any combination thereof that are joined together.

assembly drawing A document that shows the physical relation of a combination of parts and subassemblies that form a higher order assembly, giving both the locations of components and their reference designators. See Bill of Materials.

Assembly Type I/II/III see ‘ Type I/II/III Assembly’.

ASTM = American Society for Testing and Materials A US organization that provides a forum for the development and publication of test standards and procedures for materials, products, systems, and services.

ATE = Automatic Test Equipment Programmable equipment used for various testing operations within the EDR fab and assembly process. Component ATE automatically checks individual components for correct value and operation; In-Circuit Test equipment checks assemblies for correct assembly and for short-circuit and open-circuit failures on the printed circuit board; functional test equipment is used to verify the integrity of the end product. A differentiation is made between static testing, which covers individual parameters and dynamic testing, which looks at the circuit whilst it is working.

atmospheric variations Changes in operational or storage conditions. See ambient.

automated assembly Automatic component placement and attachment to a printed circuit board.

automated optical inspection (AOI) A vision system that captures and stores an image and compares it to an expected image and/or a set of design rules, in order to detect errors on printed circuit artwork, boards, or assemblies.

autoplacement The activity by CAD software that automatically places components on a circuit board layout based on preset rules.

autorouter CAD layout software that automatically determines the placement of interconnections on a circuit board based upon predetermined design rules.

axial lead A lead wire extending from a component or module body along its longitudinal axis.

azeotrope A ‘constant boiling mixture’ of two or more solvents, whose vapour has the same composition as the liquid, so that the formulation cannot be altered by distillation. Constant boiling mixtures usually have a minimum boiling point, lower than that of either of its constituents. Often azeotropes used for cleaning combine polar and non-polar solvents in order to be able to remove both polar and non-polar contaminants.

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