Flexible Circuit Board Glossary of Terms

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Access Hole

A hole in a layer of dielectric material that provides access to a land on a conductive layer of the flexible circuit.

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Acrylic Adhesive

Used to bond Multi-layered flex together and also used as part of the coverlay and stiffener used on flex layers/boards.

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Additive Process

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

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Adhesions (pressure sensitive tape)

The bond produced by contact between pressure-sensitive adhesive and a surface.

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Adhesive

A substance such as glue or cement used to fasten objects together.

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Annular Ring

 The ring of exposed solder or copper around a through hole.

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Apply a Fillet

Used the eccobond or equivalent adhesives along the rigid to flex transitions edges.

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Array

A group of elements or circuits arranged in rows and columns on a panel.

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Artwork

An accurately-scaled configuration that is used to produce the conductor pattern.

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Aspect Ratio (Hole)

The Ratio of the length of the depth of a hole to its pre-plated diameter.

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Base Material

The insulative material upon which a conductive pattern may be formed. The base material may be rigid or flexible, or both.

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Bend Ratio

A relationship between the thickness of material bent to the radius over which it is bent.

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Bending Resistance

The ability of a material to withstand repeated bending to specified parameters without producing cracks or breaks in excess of the specification allowance.

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Blind Via

A plated interconnection from one layer to an adjacent layer through a fixed depth laser drilled opening.

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Bonding Layer

An adhesive layer used in bonding together plies of dielectric and conductive materials during lamination.

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B-Stage

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.

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Buried Via

A plated through hole buried within internal layers of a circuit. There is no direct access to the via.

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Cantilevered Leads

 Unsupported conductors extending from an edge of a flex circuit.

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Cap Lamination

A process of making multilayer printed boards with surface layers of metal-clad laminates bonded in a single operation.

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Circuit

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

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Conductor Layer

The total conductive pattern formed on one side of a single layer of base material.

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Covercoat (LPI)

The material deposited as a Liquid Photo Imageable onto the circuitry that subsequently becomes a permanent dielectric coating.

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Coverfilm (Coverlayer)

A film of dielectric material with adhesive which is bonded over the etched conductor runs to insulate them.

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Delamination/Blister

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

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Dielectric

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

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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.

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Dielectric Strength

The maximum voltage that a dielectric can withstand under specified conditions without resulting in a voltage breakdown, usually expressed as volts per unit of dimension.

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Dynamic Flex

A flexible circuit designed to move during operation.

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Edge Spacing

The distance of an etched feature from the edges of a printed board.

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Flexible Printed Circuit

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

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FR4

Fiberglass reinforced epoxy laminate used as the substrate layer in a rigid flex.

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Insulation Resistance

The electrical resistance of an insulting material that is determined under specific conditions between any pair of contacts, conductors or grounding devices in various combinations.

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Land

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

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LCP

Liquid Crystalline Polymer, a relatively new dielectric substrate used in the manufacture of flex circuits.

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Micron

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

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Photo Etching

The chemical, or chemical and electrolytic, removal of unwanted portions of conductive or resistive material.

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Phototool

A phototool is a physical film 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.

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Plugged Via

When the solder mask on the rigid portion of the circuit covers the drilled via opening from one side of the board only. Optimal design is to pull the solder mask back from the via, however if coverage is required plugging should be considered as the next option before tented.

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Polyimide

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

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Pre-preg

Fiberglass reinforced epoxy adhesive used to bond layers of the flex and FR4 together in a rigid flex.

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PTH

Plated through hole. Used as a means of creating an electrical connection from one circuit layer to another.

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Rigid Flex

A circuit with one or more printed circuit boards attached by an integral flexible circuit layer.

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Sequential Lamination

The process of manufacturing multilayer printed circuit boards in which multiple double-sided layer stacks with interconnecting holes between conductive patterns on both sides are laminated or combined, after which additional layers are attached to the partially completed board stack up.

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SMT

Surface Mount Technology

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Solder Mask

Photo imageable permanent mask used for insulating rigid sections.

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Static Flex (Flex-To-Install)

A flexible printed board designed to be bent for installation purposes only (not in operation).

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Steel Rule Die

 A tool used to cut flex circuits (and other materials) from a panel.

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Stiffener

A rigid or semi-rigid material that is bonded to a flex to facilitate component attachment. Typically made of polyimide or epoxy glass.

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Tented Via

 When the soldermask on the rigid portion of the circuit spans the drilled via opening. This is not a desirable feature. Solder mask on the rigid portion of the board should be pulled back from the vias or Plugged (see definition above).

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Via Fill

Plated through hole in rigid flex which is filled with conductive or non-conductive epoxy and plated over so the resulting pad is flat and supports SMT component assembly.

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Via

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.

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Window (in the coverlayer)

An opening in the dielectric of a flexible printed board that exposes conductors.

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Windowed Leads

Conductors that are unsupported by insulation. Typically running across a window, the pitch can be quite tight allowing high density mass termination.

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ZIF (Zero Insertion Force) Termination

A style of termination that allows a flex circuit tail or tab to be inserted into a circuit board mounted connector. After insertion a mechanical actuator locks the flex in place. 

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