Flexible Circuit Glossary

Source – “Terms and Definitions for Interconnecting and
Packaging Electronic Circuits” IPC-T-50 Rev. H – July 2008


Acceptance Inspection (Criteria)

An inspection that determines conformance of a product to design specifications as the basis for acceptance.

Access Hole

A series of holes in successive layers of a multilayer board, each set having their centers on the same axis. These holes provide access to the surface of the land on one of the layers of the board.

Active Device

An electronic component that can change a signal or respond to the signal in a way that is dependent upon the nature of the signal and/or other controlling factors. (This includes diodes, transistors, amplifiers, thyristors, gates, ASIC’s and other integrated circuits that are used for the rectification, amplification, switching, etc., of analog or digital circuits in either monolithic or hybrid form).

Additive Process

A process for obtaining conductive patterns by the selective deposition of conductive material on clad or unclad base material.


A substance such as glue or cement used to fasten objects together. In surface mounting, an epoxy adhesive is used to adhere SMDs to the substrate.

Adhesion Layer

The metal layer that adheres a barrier metal to a metal land on the surface of an integrated circuit.

Adhesion Promotion

The chemical process of preparing a surface to enhance its ability to be bonded to another surface or to accept an over-plate.

Adhesive Coated Substrate

A base material upon which an adhesive coating is applied, for the purpose of retaining the conductive material (either additively applied or attached as foil for subtractive processing), that becomes part of a metal-clad dielectric.

Alignment Mark

A stylized pattern that is selectively positioned on a substrate material to assist in alignment.
(See Figure A-2).

Anisotropic Conductive Contact

An electrical connection using an anisotropic conductive film or paste wherein conductive particles of gold, silver, nickel, solder, etc. are dispersed. When it is compressed, an electrical connection is attained only in the direction of compression.

Annular Ring (Annular Width)

That portion of conductive material completely surrounding a hole. (See Figure A-4).

Figure A-4 Annular Ring (Annular Width)
Anode (BGA)

The electrode from which the forward current flows within the device.


An accurately-scaled configuration that is used to produce the “Artwork Master” or “Production Master.” (See Figure A-6.)

Aspect Ratio (Hole)

The ratio of the length or depth of a hole to its preplated diameter. (See Figure A-7).

Figure A-7 Aspect Ratio (Hole)

An intermediate stage in the reaction of a thermosetting resin in which the material softens when heated and swells, but does not entirely fuse or dissolve when it is in contact with certain liquids. (See also “C-Staged Resin.”)

Back-Bared Land

A land in flexible printed wiring that has a portion of the side normally bonded to the base dielectric material exposed by a clearance hole. (See Figure B-2).

Figure B-2
Ball Grid Array (BGA)

A surface mount package wherein the bumps for terminations are formed in a grid on the bottom of a package.
(See Figure B-3).

Figure B-3 Ball Grid Array (BGA
Bare Board

An unassembled (unpopulated) printed board.

Base Film

The film that is the base material for the flexible printed board and on the surface of which the conductive pattern can be formed. .

Bed-of-Nails Fixture

A test fixture consisting of a frame and a holder containing a field of spring-loaded pins that make electrical contact with a planar test object.


Cutting a sheet of material into pieces to the specified outline.

Blind Via

A via extending only to one surface of a printed board. (See Figure B-9.)

Figure B-9 Blind and Buried Vias

Delamination in the form of a localized swelling and separation between any of the layers of a laminated base material, or between base material and conductive foil or protective coating, or solder mask.

Bond Strength

The force perpendicular to a board&39;s surface required to separate two adjacent layers of the board, expressed as force per unit area.

Bonding Wire

Fine gold or aluminum wire used for making electrical connections between lands, lead frames, and terminals.

Buried Via

A via that does not extend to the surface of a printed board. (See Figure B-9.)

Cause-and-Effect Diagram

A problem solving tool that uses a graphic description of various process elements in order to analyze potential sources of process variation.

Characteristic Impedance

The resistance of a parallel conductor structure to the flow of alternating current (AC), usually applied to high speed circuits, and normally consisting of a constant value over a wide range of frequencies.

Chemical Resistance

The resistance of an insulating material to the degradation of surface characteristics, such as surface roughness, swelling, tackiness, blistering or color change, beyond the specified allowance by exposure to chemicals such as acids, alkalis, salts, or solvents.

Chip Carrier

A low-profile, usually square, surface-mount component semiconductor package whose die cavity or die 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-on-Flex (COF)

Semiconductor chip mounted directly onto flexible printed board.

Chip Scale Package (CSP)

The direct attachment of a chip to a substrate without an interposer.


A number of electrical elements and devices that have been interconnected to perform a desired electrical function.

Circuitry Layer

A layer of a printed board containing conductors, including ground and voltage planes.

Clearance Hole

A hole in a conductive pattern that is larger than, and coaxial with a hole in the base material of a printed board.
(See Figure C-6.)

Figure C-6 Clearance Hole
Coefficient of Thermal Expansion (CTE)

The linear dimensional change of a material per unit change in temperature. (See also “Thermal Expansion Mismatch.”)

Compensated Artwork

Production master or artwork data that has been enlarged or reduced in order to meet the needs of subsequent processing requirements.

Computer-Aided Design (CAD)

The interactive use of computer systems, programs, and procedures in the design process wherein the decision-making activity rests with the human operator and a computer provides the data manipulation function.

Conductive Foil

A sheet of metal that is used to form a conductive pattern on a base material.

Conductive Ink

A low viscosity liquid medium with a suspended powder of an electrically conductive material.

Conductivity (Thermal)

The ability of a substance or material to conduct heat.


A single conductive path in a conductive pattern that includes traces, conductive holes, lands, and planes.

Conductor Nick

A reduction in a conductor trace cross-sectional area (internal or external) which may or may not expose the base material.

Conductor Spacing

The observable distance between adjacent edges (not center-to-center spacing) of isolated conductive patterns in a conductor layer. (See Figure C-10.) (See also “Center-to-Center Spacing.”)

Figure C-10 Conductor Spacing
Conductor Width

The observable width of a conductor trace at any point chosen at random on a printed board as viewed from directly above .

Conformal Coating

An insulating protective covering that conforms to the configuration of the objects coated (e.g. Printed Boards, Printed Board Assembly) providing a protective barrier against deleterious effects from environmental conditions.


A device used to provide mechanical connect/disconnect service for electrical terminations.

Connector Housing

A plastic shell that holds electrical contacts in a specific field pattern that may also have polarization/keying bosses or slots.

Contact Resistance

The electrical resistance of metallic surfaces, under specified conditions, at their interface in the contact area.

Copper Weight

The mass of copper per unit area for a foil, typically expressed in ounces per square foot or grams per square centimeters (these units are not equivalent).


Material deposited as a liquid onto the circuitry that subsequently becomes a permanent dielectric coating (See “Cover Material”).


Film made from i) a homogeneous, single component; ii) separate layersof generically similar chemistries; or iii) as a composite blend (See “Cover Material”).


Film and adhesive made from separate layers of generically different chemistries. (See “Cover Material”).

Cpk Index (Cpk)

A measure of the relationship between the scaled distance between the process mean value and the closest specification limit.


The breaking up of large conductive areas by the use of a pattern of voids in the conductive material. (See Figure C-13).

Figure C-13 Crosshatching
Date Code

Marking of products to indicate their date of manufacture.


A separation between plies within a base material, between a base material and a conductive foil, or any other planar separation within a printed board. (See also “Blister.”)

Development (Resist)

The process of exposing a photoresist to a chemical solution which dissolves unwanted material and without affecting wanted material. The standard method of distinguishing between wanted and unwanted material is by polymerizing the resist so as to make it less soluble in the development solvent.


The uncased and normally leadless form of an electronic component that is either active or passive, discrete or integrated.


A material with a high resistance to the flow of direct current, and which is capable of being polarized by an electrical field.

Dielectric Breakdown

The complete failure of a dielectric material that is characterized by a disruptive electrical discharge through the material that is due to deterioration of material or due to an excessive sudden increase in applied voltage.

Dielectric Constant

The ratio of the capacitance of a configuration of electrodes with a specific material as the dielectric between them to the capacitance of the same electrode configuration with a vacuum or air as the dielectric. See “Permittivity.”

Differential Etching

The process of removing copper from a conductive pattern that has been plated on a starting thin copper foil such that the portions of the thin starting foil are completely removed and the thicker plated portions are slightly reduced by the etchant.

Dimensional Stability

A measure of the dimensional change of material that is caused by factors such as temperature changes, humidity changes, chemical treatment (aging), and stress exposure.

Double-Sided Printed Board

A printed board with a conductive pattern on both of its sides.

Dry Film Resist

A composite material where a photosensitive emulsion that is sensitive to portions of the light spectrum and is either carried by or sandwiched between polymer release films and is used to expose imagery on printed boards.

Edge Spacing

The distance of a pattern or component body from the edges of a printed board. (See also “Margin.”)

Electrodeposited Foil
A metal foil that is produced by electrodeposition of the metal onto a material acting as a cathode.

Etch Factor

The ratio of the depth of etch to the amount of lateral etch, i.e., the ratio of conductor thickness to the amount of undercut. (See Figure E-3).

Figure E-3 Etch Factor

The controlled removal of non-metallic materialsfrom the sidewalls of holes in order to remove resin smear and to expose additional internal conductor surfaces.(See Figure E-4).

Figure E-4 Etchback

The chemical, or chemical and electrolytic, removal of unwanted portions of conductive or resistive material. (See Figure E-5.)

Figure E-5 Etching Indicator

The process of generating a pattern within a photosensitive material through a chemical reaction using either laser direct imaging or conventional imaging with a working phototool.

Fiducial (Mark)

A printed board feature (or features) that is (are) created in the same process as the conductive pattern and that provides a common measurable point for component mounting with respect to a land pattern or land patterns.

First Article

A part or assembly that has been manufactured prior to the start of a production run for the purpose of ascertaining whether or not the manufacturing processes used to fabricate it are capable of making items that will meet all applicable end-product requirements.

Flexible Multilayer Printed Board

Multilayer printed board, either printed circuit or printed wiring, using flexible base materials only. Different areas of the flexible multilayer printed board may have different number of layers and thicknesses.

Flexible Printed Circuit

A patterned arrangement of printed circuitry and components that utilizes flexible base material with or without flexible coverlay.

Gerber Data

A type of data that consists of aperture selection and operation commands and dimensions in X- and Y-coordinates. (The data is generally used to direct a photoplotter in generating photoplotted artwork.)

Hot Air (Solder) Leveling (HASL)

A physical deposition process using a solder bath into which the printed board is immersed into a molten solder bath and withdrawn across a set of hot air knives (forced hot air flow) used to remove excess solder.

Immersion Plating

The chemical deposition of a thin metallic coating over certain basis metals that is achieved by a partial displacement of the basis metal.


The resistance to the flow of current, represented by an electrical network of combined resistance, capacitance and inductance, in a conductor as seen by an AC source of varying time voltage. The unit of measure is ohms.


Foreign particles, metallic or nonmetallic, that may be entrapped in an insulating material, conductive layer, plating, base material, or solder connection.

Laminate (n.)

A product made by bonding together two or more layers of material.

Lamination (Multilayer)

The process of bonding one or more innerlayers together with an adhesive layer or layers (such as pre-preg) utilizing a combination of heat and pressure.


A portion of a conductive pattern usually used for the connection and/or attachment of components.

Laser Direct Imaging (LDI)

The selective exposure of patterns onto a photosensitive material (such as dry film or liquid) without using a working phototool (artwork master).

Layer-to Layer-Registration

The process of aligning circuit features (lands) on individual layers of a printed board through the use of tooling image location features (fiducials) or tooling holes.

Lead Free Solder

An alloy that does not contain more than 0.1% lead (Pb) by weight as its constituent and is used for joining components to substrates or for coating surfaces.

Local Fiducial

A fiducial mark (or marks) used to locate the position of a land pattern for an individual component on a printed board.

Location Hole
A hole or notch in the panel or printed board to enable either to be positioned accurately.

Lot Size

A collection of units produced in one continuous, uninterrupted fabrication run.


A linear dimension equal to 1 x 10-6 meters or 39.4 x 10-6 inches.


A transmission line (See “Transmission Line”) structure that consists of a signal conductor that runs parallel to and is separated from a much wider reference plane. (See Figure M-3).

Figure M-3 Microstrip
Microvia (Build-Up Via)

A blind or subsequently buried hole that is < 0.15 mm [< 0.006 in] in diameter and formed either through laser or mechanical drilling, wet/dry etching, photo imaging, or conductive ink-formation followed by a plating operation.

Minimum Annular Ring

The minimum ring of metal(s) at the narrowest point between the edge of a hole and the outer edge of a circumscribing land. (This determination is made to the drilled hole on internal layers of multilayer printed boards and to the edge of the plating on external layers of multilayer and double-sided printed board.)

Nail Heading

The flared condition of copper on an inner conductive layer of a multilayer printed board that is caused by hole-drilling.
(See Figure N-1.)

Figure N-1 Nail Heading

An artwork, artwork master, or production master in which the pattern being fabricated is transparent to light and the other areas are opaque.


An entire string of electrical connections from the first source point to the last target point, including lands and vias.

Panel Plating

The plating of an entire surface of a panel including holes.

Parallel-Gap Welding

The passing of an electrical current through a high-resistance space between two parallel electrodes in order to provide the energy required to make a welded termination.

Pareto Analysis

A problem-solving technique whereby all potential problem areas or sources of variation are ranked according to their contribution to the end result.

Pattern Plating

The selective plating of a conductive pattern and associated holes.

Peel Strength

The force per unit width that is required to peel a conductor foil from a laminate perpendicular to the surface of the substrate.


A photographic process whereby an image is generated by a controlled-light beam that directly exposes a light-sensitive material.


A photo-chemically reactive material, which polymerizes upon exposure to ultraviolet energy at a given wavelength customarily used to define an etching, plating, or selective stripping pattern on a substrate.


A phototool is a physical film, Mylar (or similar), which contains the pattern that is used to produce a circuitry image on a photo-sensitive material by way of exposure to light-energy such as UV light. (see also “Artwork,” “Artwork Master,” “Production Master,” “Working Master.”)

Plating Solution

A chemical solution containing metal ions used in plating a metal-film on a substrate. Also may be referred to as an electrolyte.

Plating Void

An isolated location where the plating is absent or the plating thickness is less than the minimum specified copper thickness.


The synthetic polymer that has more than two ester radicals in the main chain.


The synthetic polymer that has more than two imide radicals in the main chain.


A sheet of material that has been impregnated with a resin cured to an intermediate stage, i.e., B-staged resin.


The degree of conformity of the position of a pattern (or portion thereof), a hole, or other feature to its intended position on a product.

Rigid-Flex Printed Board

A printed board with both rigid and flexible base materials.

Schematic Diagram

A drawing that shows, by means of graphic symbols, the electrical connections, components and functions of a specific circuit arrangement.

Screen Printing

The transferring of an image to a surface by forcing a suitable media with a squeegee through an imaged-screen mesh.

Sequential Lamination

The process of manufacturing multilayer printed boards in which multiple double-sided printed boards with interconnecting holes between conductive patterns on both sides are laminated or combined, after which additional layers (usually single-sided) are attached to the partially completed board stackup.

Shielding, Electronic

A physical barrier, usually electrically conductive, that reduces the interaction of electric or magnetic fields upon devices, circuits, or portions of circuits.


A slender portion of plating overhang that is partially or completely separated from a conductor edge.


A metal alloy with a melting temperature that is below 427 °C [800 °F].

Solder Ball

A small sphere of solder adhering to a laminate, resist, or conductor surface. (This generally occurs after wave solder or reflow soldering.)

Solder Fillet

Solder, with a normally concave surface, that is at the intersection of the metal surfaces of the solder connection.

Solder Mask .

A heat-resisting coating material applied to selected areas to prevent the deposition of solder upon those areas during subsequent soldering.


A metal or rubber blade used to wipe a material (ink or solder paste) across a stencil or silk screen to force the material through the openings in the screen or stencil, onto the surface of a printed board or mounting structure.

Stacked Via/Microvia

A via/microvia structure formed by stacking one or more build-up vias/microvias in a build-up multilayer providing an interlayer connection between three or more conductive layers.

Staking, Mechanical

The attaching of metallic devices, such as solder terminals and eyelets, by the upsetting of the portion of the device that protrudes through a hole in a base material.

Stencil (Solder Paste/Adhesive)

A thin sheet of material containing openings to reflect a specific pattern, designed to transfer a paste-like material to a substrate for the purpose of component attachment.


A method of dimensionally positioning multiples of the same or intermixed functional patterns accurately within a given area on the phototool or by repetitious contact, projection printing or photoplotting.

Stiffener Board

A material fastened to the surface of a flexible circuit to increase its mechanical strength.

Strip (Resist Stripping)

The process of removing unneeded masking material, such as a photoresist or metallic etch resist, after a processing step is completed.


A transmission line structure that consists of a signal line that runs parallel to and is sandwiched between and separated by a dielectric from two reference planes.


A plastic that undergoes a chemical reaction when exposed to elevated temperatures that leads to it having a relatively infusible or crosslinked stated that cannot be softened or reshaped by subsequent heating.


The application of molten solder to a basis metal in order to increase its solderability.

Ultrasonic Bond

A bond formed when a wire is pressed against the bonding pad and the pressing mechanism is ultrasonically vibrated at high frequency (above 10kHz).


A plated-through hole that is used as an interlayer connection, but in which there is no intention to insert a component lead or other reinforcing material. (See also “Blind Via” and “Buried Via.”)


The spreading of molten solder or glass on a metallic or nonmetallic surface, with proper application of heat and in some cases flux.


A slender, acicular metallic growth filament that is between a conductor and a land.


The capillary absorption of a liquid along the fibers of a base material. (See also “Solder Wicking”)

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