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Glossary of terms

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Term Definition
dash number   Method for using part numbers to identify and control design modifications and interchangeability of assemblies. Using a root part number with different dash numbers indicates that variations of the same functional design exist.
data file   A collection of information organized in a specific manner for a specific application.
database   A collection of interrelated data items stored together without unnecessary redundancy, to serve one or more applications.
date code   Marking of products to indicate their date of manufacture. ACI standard is WWYY(weekweekyearyear),
datum   The theoretical exact point, axis, or plane from which the location of geometric characteristics or features of a part are dimensionally established. Whence datum intersection (origin) The point of intersection of the X and Y datums on a circuit board and the origin (0,0 point) of the layout grid. The 0, 0 point of a layout grid, usually located in the lower left corner of a board.
daughter board   A PCA attached to a mother board to provide additional and/or alternate electrical functions and capabilities.
DCA (Direct Chip Attach)   See Chip-On-Board.
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 manufactured board the body of a footprint is an epoxy-ink outline.
decoupling capacitor   See bypass capacitor.
dedicated service product   Equipment or system that must perform reliably over long periods of time and experience minimum downtime, such as communication equipment, computers, and online instrumentation.
delamination   A separation between plies within the base material, between the base material and the conductive foil, or both. Occurs both in PCBs and chip ceramic capacitors.
dendritic growth   Metallic filament growth between conductors in the presence of condensed moisture and electrical bias, threatening an electrical short. (Also known as ‘whiskers’)
derating   Use of materials or components in a design at less than their rated characteristics (such as power dissipation or current-carrying capacity) to enhance the long-term reliability of the end product. Part manufacturers usually specify a derating factor to be used when a part is to be operated above a certain temperature.
design cycle   The entire technical activity associated with the design fabrication, assembly, test, and integration of a PCA
design for manufacturability  (DfM). Designing a product to be produced in the most efficient manner possible in terms of time, cost and resources, taking into consideration how the product will be processed, and using the existing skill base to achieve the highest yields possible. Checks that ensure that the design fits the fabrication process requirements. DFM includes a check for minimal trace width, minimal trace-to-trace distance, minimal hole clearance, aspect ratio, etc.
design qualification   Verification through test and analysis that a PCA design will perform its required operational functions.
design reviews   Checkpoints established at critical points in the design process to verify the validity of the design and its associated data and documentation, and evaluate the producibility, testability, and projected reliability of the product.
design rule checking   (DRC). The use of a computer-aided program to perform continuity verification of all conductors routing in accordance with appropriate design rules.
design rules   A set of layout guidelines which is used to ensure that designs meet the criteria of electronic circuit performance, ease of board fabrication and yield/cost at assembly, test and rework. Typically these rules will establish minimum dimensions and spacing, and contain recommendations on good practice. Be aware that the design rules applied by board fabricators and assemblers will vary between different companies.
design standards   Layout processes, guidelines, and procedures that are widely used throughout the industry.
Design-for-X   (DFx). The value-added service of instituting "best practices" in the design and new product introduction stages to improve X, where X is manufacturability, testability, mechanical assembly, serviceability, etc.
desmear   The removal of friction-melted resin and drilling debris from a hole wall.
desoldering methods   Disassembling solder parts to repair or replace by wicking, sucking, heat and pull, or solder extraction.
dewetting   A condition that occurs when molten solder has coated a surface and then receded, leaving irregularly shaped mounds of solder separated by areas covered with a thin solder film. Voids may also be seen in the dewetted areas. Dewetting is difficult to identify since solder may be wetted at some locations and base metal exposed at others. Depending on the location, may be caused by excessive heating, inadequate cleaning or over-oxidation of the attachment area.
DFSM (Dry Film Solder Mask)   Coating material (dry-film resist) applied to the printed circuit board via a lamination process to protect the board from solder or plating.
diametral   Pertaining to the diameter of a circle or hole.
DICY (Dicyandiamide)   The widely used but incorrect name for the dimer of cyanamide, or cyanoguanidine, which is used mainly in the production of melamine, but also as a curing agent for epoxy resins. 
die   A single rectangular piece of semiconductor material onto which specific electrical circuits have been fabricated. Refers to a semiconductor which has not yet been packaged.
die Bonder   The placement machine bonding IC chips onto a chip-on-board substrate.
die Bonding   The attachment of an IC chip to a substrate.
dielectric   An insulating medium which occupies the region between two conductors.
dielectric constant   A property that is a measure of the ability of an insulating medium to store electrostatic energy. Numerically, the dielectric constant of an insulating material is the ratio of the capacitance value when using the material, to the capacitance value of the same geometry (area and thickness) component but using vacuum as an insulator.
dielectric material   A insulating material: one that conducts no current when voltage is applied across it.
differential impedance  The impedance between two tracks that are driven in equal but opposite sense.
differential pair   Conductors carrying sensitive signals that should generally be routed in parallel with matched overall lengths.
digital   Indicates the representation of data by a series of bits or discrete values, such as 0s and 1s.
digital clock lines   Conductors that carry a continuous stream of uniform pulses (0s and 1s) that establish the timing of operation of associated digital circuitry.
digital signal processor   An integrated circuit that electronically processes signals such as sound, radio, and microwaves by converting them from analogue to digital signals.
digitising   A method of capturing the X-Y coordinates of feature locations on a PCA layout and converting that data to a digital format.
dimensional origin   See datum intersection (origin).
dimensional stability   A measure of the dimensional change of a material that is caused by factors such as temperature changes, humidity changes, chemical treatment, and stress exposure.
dimensional tolerance   The total amount that a specific dimension is permitted to vary. The tolerance defines the maximum and minimum limits of the dimension.
dimensioned hole   A hole in a printed board whose location is determined by physical dimensions or coordinate values that do not necessarily coincide with the stated grid.
DIP   (Dual In-line Package). An integrated circuit package that has two rows of pins or lead-wires for through-hole mounting positioned along opposing long sides of the package. The number of leads and the spacings between leads and between rows are all standardised, the most common spacing being 2.54mm (0.1in) between centres of adjacent pins.
dip soldering   A process whereby printed boards are brought in contact with the surface of a static pool of molten solder for the purpose of soldering the entire exposed conductive pattern and component leads in one operation.
direct imaging (DI)   An image plotter that uses a laser, which simulates a vector photo-plotter by using software to create a raster image of the individual objects in a CAD database, then plots the image onto the photosensitized material as a series of lines of dots at a very fine resolution.
discrete wire   A single cable or wire, to be terminated on to a connector contact.
dispensing (syringe)   Application of adhesives by pressurized (hydraulic or pneumatic) force for a specific period required to emit an ‘appropriate’ amount of material through the needle and onto the target location.
dispersant   A chemical additive to water to improve particulate removability.
dissipation factor   A measure of the absorption of electromagnetic energy passing through a dielectric material.
disturbed connection   A soldered connection where there is movement between the metal surfaces during solder solidification. The connection can have a dull, granular, rough, lumpy appearance and may have noticeable spiral cracks or a separation of the component lead from the solder fillet. The joint will also be of lower than average mechanical strength. Also referred to as ‘disturbed joint’.
documentation   Information for a PCB that explains the electromechanical design concept, types and quantities of parts and materials, special instructions, and revisions. Will include a Bill of Materials.
documentation/data release   The activity that takes place following final review and approval (signoff), when all drawings and design data are placed into a configuration/records control system.
dolls   To-scale cut-outs that represent physical parts to be mounted on a circuit board. They are used to perform component placement during a manual layout effort.
doping   The introduction of an impurity into a semiconductor to modify its electrical properties.
double-sided (board)   A printed board with a conductive pattern on both sides of the board.
double-track   Slang for fine line design with two traces between DIP pins.
DRAM   (Dynamic Random Access Memory). A type of memory component. ‘Dynamic’ means that the device’s memory cells need to be periodically recharged. Information stored in the memory cells, as a positive or negative charge, can be accessed randomly.
draw or flash   A designation assigned to a photoplotting aperture. A flash aperture is the size and shape of the feature it defines on photosensitive film; a draw aperture creates the shape on film via software move commands transmitted to a photoplotter.
drawbridging   A variant of tombstoning in which the component is at a small angle to the substrate rather than almost at right-angles.
drawing   Documentation that provides the configuration and requirements information needed to build a product.
DRC   Design Rule Check.
drill data   Information that specifies X-Y locations for all drilled holes, their sizes, and their plating requirements.
drill spindle run-out   The undesirable deviation from the theoretical centre of rotation of a drill spindle due to its inherent mechanical tolerances.
drill-out   A method used to modify a fabricated circuit board or assembly by drilling through a conductor (usually internal) or plated hole to break the connection.
driver   A signal source that generates an output strong enough to change logic levels of all devices (loads) attached to its net.
dross   Oxide and other contaminants which form on the surface of molten solder.
dry film solder mask   A solder mask film applied to a printed board using photographic methods. This method can manage the higher resolution required for fine line design and surface mount.
dry-film resists   Coating material specifically designed for use in the manufacture of printed circuit boards and chemically machined parts. They are resistant to various electroplating and etching processes.
dual solder wave   A wave soldering process in which an initial ‘wave’ of molten solder covers all PCB surfaces contacted. It is followed by a second laminar or ‘flat’ wave that serves to ‘finish’ the board by removing all solder bridges and icicles.
dummy traces   Added non-functional conductors that help achieve plating balance. See thieves.
DUT (Device Under Test)   Used to describe both the unit being tested and an interface board placed between the device and the computerised test equipment.
Dynamic Random Access Memory   (DRAM). The most commonly used type of volatile memory for the main memory in computing devices.