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.

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.

DEFRA: Department for Environment, Food and Rural Affairs

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 Manufacture (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.

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 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.

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.

diametral Pertaining to the diameter of a circle or hole.

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.

dielectric An insulating medium which occupies the region between two conductors.

dielectric material A insulating material: one that conducts no current when voltage is applied across it.

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.

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 tolerance The total amount that a specific dimension is permitted to vary. The tolerance defines the maximum and minimum limits of the dimension.

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.

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.

DOS = Disk Operating System A program that controls the computer’s transfer of data to and from a hard or floppy disk. Personal computers that are IBM-compatible run DOS rather than other early varieties of operating systems.

DOS-formatted (of magnetic data storage media, such as floppy disks.) Prepared for storage of data in such a way that DOS transfer can occur.

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.

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 material A photosensitive resist or solder mask material available as a film (as opposed to a liquid) that is applied to a circuit board during fabrication, using heat and pressure. Dry film solder mask can manage the higher resolution required for fine line design and surface mount, but is more expensive than liquid photoimageable solder mask.

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.