Printed Wiring Board Terms

Engineering Definitions
"A" "B" "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

Editor note; All the PWB terms are listed below. The alphabetic links above will switch to the main glossary, so scroll down the page for definitions related to Printed Wiring Boards.

'A' to 'Ge', 'Gr' to 'O', 'P' to 'R', 'S', 'T' to 'Z'

Adhesive. Adhesives are frequently used to temporarily hold SMT components in position prior to soldering. Once the soldering operations are completed, the adhesive residue is removed during the cleaning process.

The application of adhesive should be controlled to ensure proper placement, amount and cure. Excess adhesive, improper placement, or incomplete cure can contaminate solder paste and solderable surfaces,

PCB SMD Attachment
Printed Circuit Board

interfere with proper component alignment and impact cleanability. Manufacturers of Adhesive Compounds and Thermal Compounds.

Annular Ring. The portion of a conductive material that completely surrounds a hole or via. The conductive material will normally be copper, shown in yellow, to the right. Also refer to the Definition of Minimum Annular Ring, for more detail on the measurement of annular ring.

PWB Internal Via Minimum Annular Ring
Min Annular Ring

AntiPads. are clearances to provide separation between vias and voltage planes to avoid shorting the signals to the voltage rails as the via traverses the Printed Wiring Board. The diameter of the Antipad should be minimized to reduce EMI effects, but maximized to decrease shorting and voltage breakdown of adjacent signals. Antipads are small areas in prescribed shapes where copper is removed. Antipads are used mainly with vias.

Artwork: The drawings that represent the board design.

Assembly: A collection of parts and components attached to a printed circuit board. A functional subdivision of a component, consisting of parts or sub-assemblies that perform functions necessary for the operation of the component as a whole.

Assembly Drawing: A drawing that details the construction of a PWB and their associated components. An Assembly drawing determines the final construction of a unit, formed by a number of components. In this case a PWB and each of its component parts or components.

Automated Test Pads: Copper pads added to the PCB design to accommodate bed-of-nails pins during automated testing of the circuit board. Bed-of-Nail test pads are added to nets on the PWB that would not normally require a pad or via, but are only added to assist with bare board testing. Note the trade off is some nets may not require a via or test pad, but the continuity test may require them. Also see Test Pads.

Copper Test Pads for Automated Testing
ATE Test Pads

Backplane: A card designed to accept other cards that plug into the backplane. This could be a card-edge to connector interface [as in a PC] or a connector to connector interface [as in a number of embedded systems]. Normally backplanes are 0.90 or thicker.

Rear View 3U 8-Slot cPCI Backplane
cPCI Backplane

Refer here for styles and Manufacturers of Back-planes.

Bifurcated (split) Terminal: A terminal with a slot or split opening in which conductors are placed before soldering.

Blind Via. A via (plated-through hole) that extends to only one surface (primary / secondary) of a multilayer printed wiring board, with the other end terminating to an internal plane or land.

Blister: Raised areas on the surface of the laminate caused by the pressure of volatile substances entrapped within the laminate.

Blow Hole: A cavity in the solder surface whose opening has an irregular and jagged form, without a smooth surface.

Board Material: Data on Board Materials

Bond: A bond is an electrical union between two metallic surfaces used to provide a low-impedance path between them. Bonding is the procedure by which the conductive surface of a subassembly or component is electrically connected to another. This prevents development of electrical potentials between individual metal surfaces for all frequencies capable of causing interference.

BondPly: A prepreg material used with flexible circuit. Also seen as Bond-Ply, or Bond Ply. A Thermally Conductive, Film Reinforced, electrically insulating, double-sided Pressure Sensitive Adhesive Tape.

Bow and Twist: Board warpage. The degree to which the PWB is not flat. The maximum allowable bow and twist shall be as specified 1.5 percent.

Bridging: A buildup of solder between components, conductors, and/or base substrate forming an undesired conductive path.

Buried via: A via hole not extending to the surface.

Chip On Board: See COB.

Circuit Card Assembly: [CCA]. A Printed Circuit Card with all of its components installed to form a complete assembly. Pic; ATI FireMV 2260 graphics card.

ATI PCIe Graphics Card, ATI FireMV 2260 graphics board
ATI Graphics CCA

COB: Chip on Board. An MCM integrated bare die mounted directly on to the interconnect substrate. Refer here for vendors COB Packaging.

Cold Solder Connection: A solder connection exhibiting poor wetting and a grayish, porous appearance due to insufficient heat, inadequate cleaning before to soldering, or excessive impurities in the solder.

Compliant Pin: Compliant pin technology is a press-fit, solder-free process used to interconnect pins and tabs to a PCB. [Read more on Compliant pins]

Component Side. The primary side of a printed wiring board, from which through-hole components are typically inserted and which is opposite the solder application side of the board in solder wave assembly processes. The majority of the active circuit components typically populate the component / primary side. See also Solder Side.

Computer Aided Design: [CAD]. Also called Computer Aided Engineering [CAE]. CAD systems are Software programs designed to enhance engineering design and automation. There are a number of software programs designed to perform Printed Wiring Board [PWB] layout. Vendors producing CAD Software Tools and programs.

PWB CAD Layout with CAD Design
CAD Output

Conductor Spacing: The distance between two conductors. The table below indicates the Conductor Spacing between a signal trace and power trace or island. However the term trace separation [below] refers to the separation between two different signal traces.

Conductor Spacing per MIL-STD-275
Voltage Between Conductors
Minimum Trace Spacing
DC or AC peak volts
Surface Layers Internal Layers
0 - 100v
0.005" 0.004"
101 - 300v
0.015" 0.008"
301 - 500v
0.030" 0.010"

Conformal Coating: An insulative coating that conforms to the configuration of the object being coated. Conformal coating is a thin layer of dielectric material which applied to a printed wiring board that provides environmental and

Conformal Coating CCA
Printed Circuit Board

mechanical protection to the circuits on the PWB. Manufacturers that produce Conformal Coatings and additional data relating to Conformal Coating.

Controlled Impedance: A copper trace running over a copper ground or power plane which has a tightly controlled impedance.

Copper Fill: A technique that introduces areas of copper on the portions of the PCB surface that carry no signals and therefore should be grounded.

Copper Plating: See Plating. Reference; MIL-C-14550B - Copper Plating, (Electro-Deposited).

Core Material. A thin dielectric that has copper foil bonded to both sides. The most common dielectric used is fiber glass. The core material may be used as a two layer board or in a multi-layer board with interleaved layers of prepreg between the core material(s). The copper foil is used to carry the circuit traces or interconnects and the fiber glass is used to insulate and separate the two copper foils.

Coupon: See Test Coupon.

Crazing: The presence of numerous minute cracks in the referenced material.

Cu: Copper. The most common metal used as a conductor on PWB's.

Current Capacity: The amount of current a PWB trace can handle before it melts. The amount of trace Current Capacity differs between an internal layer and an external layer; Refer to PWB Etched External Copper Current Capacity, PWB Etched Internal Copper Current Capacity.

Datum: A reference point from which measurements are taken on the PWB. There should be a minimum of two datum features to established the mutually perpendicular datum reference frame for each board. These datums shall be established by at least two holes, points, or symbols, but not edges.

Dead-Bug. An industry nickname for the discrete components added and wired into a printed wiring assembly (PWA) to facilitate circuit modifications, rather than redesign and manufacture a new board. The nickname comes from their general appearance on the board: upside down, with their termination leads (legs) up in the air, like a dead bug.

DeadBug Transistor

Component Mounting

Delamination: A separation between plies within a base material or any planar separation within a multilayer PWB.

Die: The semiconductor wafer cut into individual dies. The Die is the silicon portion of an integrated circuit [IC]. The silicon Die is secured to a base material, wire bonded to its leads and then capped to form an integrated circuit. Pic; AMD Phenom Quad-Core Processor Die.

AMD Phenom Quad-Core Processor Die
Semiconductor Die

Die bonding: The attachment of an integrated circuit chip to a substrate or header. The Packaging Dictionary contains the term Bonding Pads.

Dielectric: An insulating (non-conducting) medium.

Dielectric Constant: A measure of the ability to support an electrostatic field related to capacitance, with units [Er] in Farads/meter. Refer to the Board Materials page for a PWB Permittivity Graph.

Dog Bone Via: A land pattern style that connects a solder pad and via using a thinner copper trace between the two pads. Refer to the graphic to the right. This type of pad to via connection is used in high density pad arrays, under an FPGA for example.

Double-Sided Assembly. A printed wiring assembly (either double-side or multi-layer) with components mounted on both the primary (component) and secondary (solder) sides.

Edge Mount: A Card-to-Card mounting method where by one card uses copper fingers and the other card uses a mounting counter. The card using the fingers is normally the daughter card while the card utilizing the connector is the mother-board.

PCB Edge Mount Board
PWB Fingers

Encapsulate: To seal or cover an element or circuit for mechanical and environmental protection.

Encapsulating Compound: An electrically non-conductive compound used to completely enclose and fill in voids between electrical components or parts.

ESD: Electrostatic Discharge. [Read more on ESD Definitions]. Printed Wiring Boards are not ESD sensitive. However; board assemblies are, once components and ICs are attached to the PWB. Regardless the ESD warning label is placed on almost all packing regardless of any potential problem.

ESD Symbol
ESD Warning Label

Etchback: The process of fabricating a Plated Through Hole [PTH] in a PWB which causes either the copper lands [of the PTH] to be recessed (Negative Etchback), or the dielectric material to be recessed (Positive Etchback). Positive etchback provides a greater amount of the copper land to come in contact with the plating material providing a more reliable bonding connection [plating to copper land].

Eutectic Solder: An alloy of 63 percent tin and 37 percent lead. Melts at 3610 F.

Eyelet: A hollow tube inserted in a terminal or PWB to provide mechanical support for component leads or for electrical connection.

Fabrication Process: The manufacturing process used by a PCB vendor to produce the bare printed wiring board.

Fiducial Mark. An artwork feature that provides a visual guide for component orientation and mounting.

Fillet: A smooth concave buildup of material between two surfaces; e.g., a fillet of solder between a conductor and a solder pad or terminal.

Flexible Laminate: A flexible printed wiring board. For Military designs flexible and rigid-flex printed wiring should conform to MIL-HDBK-1861 and should be designed in accordance with MIL-HDBK-1861. Also called a Flexible Circuit Board [FCB].


Flux: A chemically-active compound which, when heated, removes minor surface oxidation, minimizes oxidation of the basis metal, and promotes the formation of an intermetallic layer between solder and basis metal. Also refer to MIL-F-14256; Flux, Soldering, Liquid (Rosin Base).

Footprint: The area occupied on the substrate by a component or element.

FR4: [Fire Retardant 4] A material used as a Printed Wiring Board [PWB] material.

Gerber File: A file format used by printed circuit board designers to layout electrical connections such as traces, vias, and pads on the PCB.

PC motherboard

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