PCB Glossary & Abbreviations

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Annular ring

Copper land surrounding a hole. Review the finished geometry and the required acceptance condition.Fabrication

AOI — Automated optical inspection

Camera-based inspection against defined criteria. It does not directly inspect every hidden joint or establish electrical function.Quality & documents

Aspect ratio

A depth-to-diameter relationship used for holes or vias; state which depth and diameter are being compared.Fabrication

AXI — Automated X-ray inspection

Automated X-ray examination of internal or obscured features against a defined inspection program.Quality & documents

Backdrill

Controlled-depth removal of an unused plated via-barrel segment.Fabrication

Bare-board test

Electrical testing of the unpopulated PCB, commonly for connection and isolation requirements.Quality & documents

BGA — Ball grid array

A package whose external interconnections are arranged as an array of solder balls.Assembly

Blind via

A via joining an outer layer to an internal layer without crossing the entire board.Fabrication

BOM — Bill of materials

The specified component list for an assembly, tied to the design revision.Quality & documents

Buried via

An internal-layer connection that does not reach either external board surface.Fabrication

CAD — Computer-aided design

Software-based creation and editing of design information, including schematics and board layouts.Quality & documents

CAM — Computer-aided manufacturing

Preparation and processing of design data for the manufacturing workflow.Fabrication

CCL — Copper-clad laminate

Insulating laminate supplied with copper cladding for circuit fabrication.Materials

CoC — Certificate of conformity

A supplier declaration against stated requirements. Check the referenced product, revision and scope.Quality & documents

Controlled impedance

A specified transmission-line impedance requirement supported by defined geometry and fabrication acceptance.Signal integrity

Copper weight

Copper mass per unit area, often expressed in oz/ft²; it is not a complete finished-thickness specification.Materials

Core

A cured laminate used as part of a multilayer construction.Materials

CPL — Component placement list

Placement data identifying where and how components are positioned; coordinate and rotation conventions must be agreed.Assembly

Crosstalk

Unwanted coupling between signal paths.Signal integrity

CTE — Coefficient of thermal expansion

Relative dimensional change with temperature; specify the direction and temperature range.Materials

Df — Dissipation factor

A dielectric-loss parameter; compare values under matched frequency and test conditions.Materials

DFA — Design for assembly

Reviewing a design for practical, consistent assembly.Assembly

DFM — Design for manufacturing

Reviewing design information against the intended manufacturing process and agreed constraints.Fabrication

DFT — Design for test

Providing access and design features needed for the planned verification.Quality & documents

Dk — Dielectric constant

Relative permittivity. Modeling and process-control values may differ; identify the intended use.Materials

DRC — Design-rule check

An automated check against configured layout rules. Passing only proves those rules were checked.Quality & documents

ENEPIG

Electroless nickel, electroless palladium and immersion gold: a multilayer surface-finish system.Materials

ENIG

Electroless nickel and immersion gold: a surface-finish system, not hard-gold contact plating.Materials

ESD — Electrostatic discharge

Transfer of electrostatic charge; apply handling controls appropriate to the devices and process.Quality & documents

FAI — First article inspection

A planned inspection of an initial article against specified requirements, with the agreed records.Quality & documents

FCT — Functional circuit test

Testing an assembly’s specified functions under defined conditions; coverage depends on the test plan.Quality & documents

FEFO — First expiring, first out

An inventory rule prioritizing stock with the earliest applicable expiry or review limit.Quality & documents

Fiducial

A visual reference used for optical alignment.Assembly

FPC — Flexible printed circuit

A circuit using a flexible substrate construction. Bending requirements remain application-specific.Fabrication

FR-4

A glass-reinforced flame-retardant epoxy-laminate designation, not one universal material grade.Materials

Gerber

A PCB data-exchange format for layer images and associated attributes; confirm the required fabrication data set.Quality & documents

GND — Ground

A named reference or return net. Its label alone does not guarantee a continuous return path.Signal integrity

HASL — Hot-air solder leveling

A solder-coated finish leveled with hot air. Specify leaded or lead-free rather than assuming the alloy.Materials

HDI — High-density interconnect

An interconnect approach using fine features and advanced via structures; define the actual construction.Fabrication

HIC — Humidity indicator card

A packaging indicator of specified humidity exposure conditions, not a direct laminate-moisture measurement.Quality & documents

ICT — In-circuit test

Electrical tests of selected nets or components on an assembly, subject to access and test coverage.Quality & documents

Impedance coupon

A test structure fabricated with the panel to represent specified controlled-impedance constructions.Quality & documents

IMS — Insulated metal substrate

Circuit copper separated from a metal base by an insulating dielectric layer.Materials

LGA — Land grid array

A package with an array of conductive lands rather than external solder balls.Assembly

LPI — Liquid photoimageable

A liquid-applied coating patterned by photographic processing; commonly used for solder mask.Materials

MBB — Moisture barrier bag

Packaging designed to limit moisture ingress as part of a specified dry-pack system.Quality & documents

MCPCB — Metal-core PCB

A board construction incorporating a metal core or base; specify the actual layer architecture.Materials

Microsection

A prepared cross-section used to examine internal construction and features.Quality & documents

Microstrip

A transmission-line structure with a surface conductor and a reference plane separated by dielectric.Signal integrity

Microvia

A small interlayer connection with a defined microvia construction; state the governing criteria, depth and geometry.Fabrication

Mil

One thousandth of an inch: exactly 0.0254 mm. It is not a millimeter.Quality & documents

MSL — Moisture sensitivity level

A classification concerning a component’s moisture/reflow susceptibility and associated handling requirements.Assembly

NPTH — Non-plated through hole

A hole through the board without a specified plated conductive barrel.Fabrication

NSMD — Non-solder-mask-defined pad

A pad whose copper perimeter, rather than an overlapping mask opening, defines the exposed pad area.Assembly

Open circuit

A missing electrical connection where continuity is required.Quality & documents

OSP — Organic solderability preservative

An organic protective treatment on exposed copper for subsequent soldering.Materials

Pad / land

A conductive feature used for a connection, component attachment or access point.Fabrication

Panelization

Arranging boards and any necessary process features into a manufacturing or assembly panel.Fabrication

PCB — Printed circuit board

The board carrying the patterned conductive interconnections; distinguish it from its populated assembly.Fabrication

PCBA — Printed circuit board assembly

A PCB with components installed through the specified assembly process.Assembly

PDN — Power distribution network

The network delivering power and providing associated return paths, including relevant interconnects and decoupling.Signal integrity

PI — Power integrity / polyimide

Context matters: PI can mean power integrity in electrical design or polyimide in a material specification.Signal integrity

Prepreg

A partially cured resin-impregnated reinforcement used in laminate bonding.Materials

PTH — Plated through hole

A through hole with a plated conductive barrel. State finished-hole requirements separately from tool size.Fabrication

QFN — Quad flat no-lead

A leadless package with connection lands around its perimeter; an exposed thermal pad may also be present.Assembly

Reflow

Soldering by heating previously applied solder, typically solder paste, through a controlled process.Assembly

RF — Radio frequency

Frequency-domain usage associated with radio and related electromagnetic applications; state the actual frequency range.Signal integrity

RFQ — Request for quotation

A request for pricing and scope against a defined project specification.Quality & documents

RoHS

Restriction of Hazardous Substances: an EU framework whose scope, restricted materials and exemptions must be assessed.Quality & documents

Routing

May mean connecting nets in layout or mechanically machining the board profile. State the context.Fabrication

SAC305

A tin/silver/copper lead-free solder alloy: nominally 96.5% Sn, 3.0% Ag and 0.5% Cu.Materials

Short circuit

An unintended electrical connection between conductors or nets.Quality & documents

SI — Signal integrity

Assessment of signal quality through an interconnect, including reflections, loss and coupling.Signal integrity

Silkscreen / legend

Printed identification and reference markings on a PCB.Fabrication

SMD — Two common meanings

Surface-mount device, or solder-mask-defined pad. In the second meaning, mask overlaps the copper perimeter to define exposure.Assembly

SMT — Surface mount technology

Assembly of components onto surface lands rather than inserting their leads through mounting holes.Assembly

Solder mask

A patterned protective coating leaving intended connection areas exposed.Materials

SPI — Solder paste inspection

Inspection of printed solder-paste deposits before or during the assembly sequence.Quality & documents

Stackup

The ordered copper and dielectric construction of a PCB.Fabrication

Stencil

An apertured template used to deposit solder paste in defined locations.Assembly

Stripline

A transmission-line conductor embedded in dielectric between reference planes.Signal integrity

TAL — Time above liquidus

The portion of a thermal profile spent above the relevant alloy’s liquidus temperature.Assembly

TDR — Time-domain reflectometry

Characterizing an interconnect from the reflections of an applied fast transition.Signal integrity

Tg — Glass-transition temperature

A material-transition temperature whose reported value depends on the measurement method; not a maximum-use rating.Materials

Thermal via

A via intentionally included in a heat-transfer path; assess it as part of the complete thermal design.Fabrication

Trace / track

A patterned conductive route on a circuit layer.Fabrication

V-score / V-cut

Grooves used to define separation lines between boards in a panel.Fabrication

Via-in-pad

A via placed within a pad. Define the fill, cap and finished-surface requirements where the assembly needs them.Fabrication

Z0 — Characteristic impedance

The transmission-line impedance for a defined structure and propagation mode.Signal integrity

Zdiff — Differential impedance

The impedance seen by differential excitation. For a symmetric pair, Zdiff equals twice its odd-mode impedance.Signal integrity