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. They may assist in performing all steps in artwork generation.

CAD/CAM A concatenation of the terms CAD and CAM. CAD/CAM systems are computer-aided design/manufacturing methods that translate circuit designs into actual products.

CAE = Computer-Aided Engineering ( Computer Assisted Engineering) A software package used as an automated tool for circuit design and schematic generation.

CAF = Conductive Anodic Filament. Metal migration between two conductors or the dendritic growth seen under Temperature, Humidity and Bias test.

CAM = Computer-Aided Manufacturing system A system used to generate data for fabricating circuit boards and manufacturing finished assemblies. CAM files are data files used directly in the manufacture of printed wiring. Typically this data is manipulated by the fabricator to meet production requirements (for example for panelisation) and to ensure the intended result is achieved.

Some design software companies refer to all plotter or printer files as CAM files, although some of the plots may be check plots which are not used in manufacture.

capacitance The property of a circuit element that permits it to store an electrical charge.

capacitor A discrete device that stores an electrical charge on two conductors separated by a dielectric.

capillary action The combination of force, adhesion and cohesion that prompts liquids, such as molten solder, to flow upward between closely spaced solid surfaces, e.g., lead (contact) and pad.

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

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 to be plugged directly into another much larger printed board, the motherboard or back-plane. See finger.

carriers Holding devices for PCBs and other parts to facilitate handling during component placement, soldering and other processing.

castellation Metallised semicircular radial features on the edges of LCCCs that interconnect conducting surfaces. Castellations typically are found on all four edges of a leadless chip carrier. Each lies within the termination area for direct attachment to the land patterns.

CBGA = Ceramic Ball Grid Array (also Column BGA) Less common than the standard ball grid array, which uses balls of eutectic solder, CBGAs contacts are columns of a high-melting solder. When reflowed in contact with eutectic solder on the substrate, only a small portion of the column melts into the joint, so that the package is held off the substrate. The resultsing separation gives a degree of flexibility which allows for differences in CTE between the ceramic body of the CBGA and the FR4 board.

cell A tiny area within the memory array that actually stores the bit in the form of an electrical charge.

centroid A point whose coordinates are the average of an associated parts dimensions (central point).

CFC = chlorinated fluorocarbon Causes depletion of ozone layer and scheduled for restricted use by the Environmental Protection Agency. CFCs are used in air conditioning, foam insulation and solvents.

chamfer To bevel or round an otherwise sharp or blunt edge. (Also see ‘ bevel’)

chassis The supporting frame or structure that houses printed circuit assemblies.

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

chemical stability The ability of the characteristics of a material to remain unchanged by aging or variations in the environment.

chip carrier A low profile surface-mount component package, usually square, whose conductor chip cavity or mounting area is a large fraction of the package size and whose external connections are usually on all four sides of the package. It may be leaded or leadless.

chip component Generic term for any two-terminal leadless box-shaped surface mount passive device, such as a resistor or capacitor. Also known as ‘discretes.’

chip on board see COB

chip package A carrier in which an IC chip is mounted. The package interconnects the chip to the outside world and is sealed to provide environmental protection for the chip.

circuit (circuitry) The interconnection of a number of electrical elements and/or devices to perform a desired electrical function.

circuit coupling The creation of a false signal in a circuit by a signal in another circuit. This is usually caused by radiated energy between adjacent conductors on the same or different layers.

circuit density The proportion of circuit elements and interconnections required for performing an electrical function to the allotted area of a circuit board.

circuit fault Incorrect performance of a circuit resulting in a specific error. In digital circuitry this could manifest itself as a logic error. During functional testing, artificial faults are sometimes injected into a circuit to verify the tester’s ability to identify them correctly.

circuit filter Protective circuitry designed to prevent transmission of unwanted current or voltage deviations during operation.

circuit frequency Usually pertains to the operating speed of a circuit and is a function of the types of components used, the dielectric properties of the circuit board( and the physical characteristics of the circuit conductors (dimensions/shape).

circuit net See net.

circuit symbol Used in a schematic diagram as a graphic representation of a specific type of electronic device.

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.

cladding A thin layer of metal foil bonded to a substrate to form the conductive PCB pattern.

clamshell fixture An in-circuit test fixture that permits simultaneous probing of both sides of a board or assembly. The top probe section is hinged to allow board insertion.

cleanroom The super-clean environment in which semiconductors are manufactured. The lower the rating (e.g. Class 100), the cleaner the facility. These rooms typically have hundreds of thousands of particles less per cubic metre than the normal environment.

Climate Change Levy: A tax introduced on 1 April 2001, which is designed to stimulate business improvements in energy efficiency.

clinched lead A component lead passed through a hole in the printed circuit board, that has been formed to prevent the component from falling out during soldering.

clinching The process of forming or bending a component lead following its insertion through a hole in a circuit board. The main purpose is to secure the part mechanically during the soldering process.

clock speed The switching frequency of the clock circuit in digital logic. It is principally determined by the rise/fall time required for the digital devices used in a circuit to change logic state (from 0 to 1 or vice versa).

closed bottom contact The back of the contact is closed to prevent solder ingress, usually this applies to PCB and solder tail contacts.

closed entry socket The entry for the mating plug contact is such as to prevent damage to the socket contact on insertion.

CMOS Complementary Metal Oxide Semiconductor. A MOS device containing both N-channel and P-channel MOS active elements. One of two basic processes (MOS and bipolar) used to fabricate integrated circuits.

COB = Chip-On-Board Generic term for any component assembly technology in which an unpackaged silicon die is mounted directly on the substrate, instead of first being packaged. Connections from die to the pads on the board can be made by wire bonding, tape automated bonding (TAB), or flip-chip bonding. For commercial use the die is protected by a plastic ‘glob top’, usually black in colour.

Coefficient of Thermal Expansion See CTE.

cohesive characteristics See adhesive characteristics.

cold (solder) joint A solder connection exhibiting poor wetting and of greyish, porous appearance due to insufficient heat or excessive impurities in the solder. The condition can be caused by applying insufficient heat to the joint, inadequately cleaning the surfaces prior to soldering, insufficiently heating the part being soldered, improper tinning of the soldering iron tip, or poor heat control.

compliant press-fit terminations are contacts in a connector where the tails are formed to have a compliant section. This section deforms as the tail is pressed down into the plated through hole of the printed circuit board. The inherent spring force in the compliant section retains contact during the life of the equipment without the need for a soldering operation.

component A separate part of a printed board assembly which performs a circuit function. Active devices, such as resistors, capacitors, or semiconductors, have distinct electrical characteristics that perform specific functions in a circuit and with terminals which may be inserted into or mounted on, a printing wiring board to form a printed wiring assembly. connector

component hole A hole used for attachment and electrical connection of component terminations, including pins and wires (‘leads’), to the printed board.

component lead extension The distance a through-hole component lead extends beyond the surface of a circuit board after soldering.

component lead See lead.

component metallisation see component termination.

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

component mounting orientation The direction in which the components on a printed board or other assembly are lined up, with respect to one another, to the solder wave, and to the board.

component side The primary side of a printed board upon which the major of component parts are mounted. Where size allows, the component side may be printed with the ‘legend’. (Also see ‘ topside’)

component termination This term can refer to a lead, but is more commonly a description applied to the interface between the body of the component and the board in a leadless device. Termination materials need to adhere to the component, forming a reliable connection, and be wettable by (but not soluble in) the solder used for attachment to the board. Typically, for a chip component, this termination will be made of several layers, with a ‘solder barrier’ (a material insoluble in solder) underlying a (usually thinner) layer of something highly solderable.

condensation soldering A general term referring to a method of heating where an assembly is submerged into a hot, relatively oxygen-free, vapour. The vapour condenses on the relatively cool surface of the assembly, transferring its latent heat of vaporization to the parts being soldered. Also known as vapour phase soldering.

conduction The ability of electrons to flow through a conductor. It is the reciprocal of resistance. Conduction is also a heat transfer mechanism in solid materials, involving transfer of kinetic energy within its molecular structure.

conductive adhesive see anisotropic conductive adhesive and isotropic conductive adhesive.

conductive foil A thin sheet of metal (usually copper) that covers one or both sides of the base laminate and is intended for forming the conductive pattern on a printed circuit board. (Also referred to as ‘cladding’ or ‘foil’)

connector mating and un-mating force The total force required to plug and unplug connectors, made up of the sum of the individual contact forces plus any friction due to housing misalignment.

contact bounce Movement causing an open-circuit between a male and female connector contact or in a relay. This can occur due to vibration conditions during service, or during the plugging together operation of a connector.

contact carrying capacity The maximum current a mating pair of contacts, or all contacts in a connector or relay simultaneously, can pass without causing degradation due to overheating and thermal stress. This is usually specified at room temperature and at maximum operating temperature, with a de-rating curve in between.

contact rating The maximum and minimum voltage, current and power that a contact pair can be guaranteed to operate with under specified environmental conditions.

contact retention The specified force at which contacts will start to receive damage or pull out of a connector housing.

contact size Defines the maximum wire size that can be used with a contact in a cable connector. This determines the contact diameter and current rating.

copper foil See conductive foil.

conductive ink The paste used on thick film materials to form the circuit pattern, usually containing metal, metal oxide and solvent.

conductor (conductive) pattern The configuration or design of the conductive material on the base laminate, including conductors, lands, vias, heat-sinks and passive components when these are an integral part of the manufacturing process.

conductor A current-carrying interconnection path. A single conductive path in a conductive pattern. Also known as a ‘trace’.

conductor layer The total conductor pattern formed on one side of a single layer of laminate material.

conductor pattern The configuration or design of the conductive material on one side of a single layer of base material.

conductor separation Permanent separation of the printed wiring conductive foil from the base laminate. (Also see ‘ delamination’)

conductor side The side of a printed board containing the conductors. Commonly referred to as the ‘solder side’ when opposite through-hole components. (Also see ‘bottom side’)

configuration control A method for ensuring that a specific version of data and drawings defines the correct requirements and physical description of the intended version of a PCA, and that the actual hardware conforms in all respects to the data and drawings.

conformal coating An insulating protective coating applied to the completed board assembly, which conforms to the configuration of the objects coated and provides a barrier against deleterious effects of their environment.

connection (US ‘connexion’) 1) Joining or linking to make an electrical contact to, or circuit with, the conductive pattern. 2) 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 device that provides a mechanically pluggable interface for electrical terminations. 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.

constraining core substrate A composite PCB consisting of epoxy-glass layers bound to a low thermal expansion core material, such as copper-invar-copper, graphite-epoxy and aramid fibre-epoxy. The core constrains the expansion of the outer layers to match the expansion coefficient of ceramic chip carriers.

contact angle The angle of wetting between the solder fillet and termination or land pattern. A contact angle is measured by constructing a line tangential to the solder fillet that passes through a point of origin located at the plane of intersection between the solder fillet and termination or land pattern. Contact angles of less than 90° (positive wetting angles) are acceptable. Contact angles greater that 90° (negative wetting angles) are unacceptable.

contact resistance The resistance in the conductive path between two touching surfaces. It relates primarily to resistance across mating connector contacts.

contaminant An impurity or foreign substance whose presence on an assembly could electrolytically, chemically, or galvanically corrode the system.

continuity test A test for the presence of current flow between two or more interconnected points.

controlled waste: The UK term for wastes controlled under the Waste Framework Directive: any household, industrial or commercial waste.

convection The mechanism for transfer of heat from a solid surface (such as a component) to a surrounding fluid (usually air). Natural convection is heat transfer to ‘still’ air; forced convection involves heat transfer to air that is moved by artificial means such as a fan.

convection/IR A solder reflow oven for SMD interconnect that combines convection and infrared (IR) radiation heating.

conveyor A PCB transporting system for moving assemblies to various processes. An edge conveyor supports the boards at opposite sides; a mesh conveyor fully supports the board. On reflow ovens, a secondary mesh conveyor is often located below the edge mechanism to catch fallen components.

coplanarity The leads of a package should be ‘coplanar with’ the PWB, that is, there should be no gap between the leads and a flat board. If they are not, the non-coplanarity problem can result in open-circuit joints. The term coplanarity is however usually (somewhat incorrectly) used to refer to the maximum distance between the surface and the highest pin when the package rests on a perfectly flat surface. A typical specification for coplanarity is not greater than 0.1mm.

copper weight A measurement of the thickness of copper foil, in terms of its weight in ounces per square foot of surface area. 1-ounce copper is nominally 35µm (0.0014 in) thick, ½-ounce copper is 18µm (0.0007 in thick.

copper-clad dielectric material The basic material used for fabricating a printed circuit board, consisting of a flat reinforced dielectric to which is bonded copper foil on one or both surfaces.

core A supporting plane that is internal to a packaging and interconnecting structure. Multilayer circuit boards may contain unclad laminate cores, or special-purpose cores made of metal (aluminium, copper) to enhance heat dissipation or for other purposes.

corrosion Gradual destruction of a metal or alloy due to chemical processes such as oxidation or the action of a chemical agent.

corrosive A substance that causes corrosion; chemically reactive with ability to wear away gradually.

cost-benefit (trade-off) study The analysis of the cost of implementing each of an alternative (design/manufacturing/assembly/test) approach (or solution to a problem) versus the benefits of doing so.

covers (or hoods) Used on cable connectors to protect and insulate the terminations.

CPU Central Processing Unit. The computer module in charge of retrieving, decoding, and executing instructions.

crazing An internal condition existing in the laminate base material in the form of connected white spots or crosses on or below the surface of the base laminate, reflecting the separation of glass fibres from resin at the connecting weave intersections. Crazing is usually related to mechanically-induced stress. (Also see ‘ measling’)

critical signal paths Conductors carrying signals that may be particularly sensitive to distortion by external signals, and require routing in specific locations on a board, or layout in a specific physical geometrical configuration.

cross-hatching The breaking up of the large PWB conductor areas by the use of a pattern of voids.

crosstalk See circuit coupling.

CSP = Chip-Scale Package The Chip-Scale Package exists in many forms, often employing BGA and flip-chip elements. Regardless of the construction, the aim is to create a high-density IC package only slightly larger than the chip. A number of definitions have been proposed, of which the most usual is that the package should be no more than 1.5 times the chip in area and no more than 1.2 times the chip in linear dimension.

CTE (Coefficient of Thermal Expansion) The rate at which a material changes dimension as its temperature is increased. Can refer to the linear dimensions or the volume of the material. Expressed as the fractional change in dimension divided by the change in temperature, most commonly as ppm/°C. Often referred to as thermal coefficient of expansion (TCE).

Note particularly that:

• CTE is not a linear function of temperature, it being quite common for materials to expand and shrink differently at different temperatures. For example, water first shrinks and then expands as it cools, having a maximum density at around 4°C.
• CTE is not necessarily isotropic, that is, the same in all directions. Most metals are isotropic, but most laminate materials have a CTE in the Z axis (through the thickness of the laminate) which is different from that of the XY axis (in the same plane as the laminate). Stresses from the higher Z-axis expansion have a major impact on the reliability of through-hole metallisation.

curing agent A chemical added to a resin to stimulate a final set or hardening.

current rating The maximum allowable continuous current that can be passed through a component or a conductor without causing degradation of performance.

cuts Modification of a circuit board by separating conductors on an external layer to break a circuit connection.

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