Technical Glossary
Flex Circuit
Definitions & Glossary
A complete technical reference for flexible circuit terminology — from access holes and additive process to ZIF termination and windowed leads.
Technical Reference
Flex Circuit Definitions
Complete glossary for engineers, designers, and procurement teams.
Access Hole
Holes in successive layers of a multilayer board providing access to a land on an inner layer.
Additive Process
Selective deposition of conductive material to create circuit patterns — enables finer features than subtractive etching.
Annular Ring
The ring of exposed copper around a plated through hole.
Blind Via
PTH from one layer to an adjacent layer through a laser-drilled opening of fixed depth.
Buried Via
PTH connecting inner layers with no surface access.
Cantilevered Leads
Unsupported copper conductors extending from a flex circuit edge for ZIF or pressure contact termination.
Coverlayer
Bonded polyimide insulating layer over conductor pattern — protects and insulates.
Dielectric
High-resistance material capable of being polarized by an electric field. KAPTON polyimide in flex circuits.
FR-4
Fiberglass reinforced epoxy — rigid substrate in rigid-flex and stiffener material in flex.
KAPTON®
DuPont polyimide film — the primary flex circuit substrate. Exceptional thermal stability. Survives 500M+ flex cycles.
Land
A conductor pad used for component attachment or interconnection.
LCP
Liquid Crystalline Polymer — advanced dielectric with excellent HF performance and low moisture absorption.
Photo Etching
Chemical removal of unwanted copper using a phototool-defined resist pattern.
Phototool
Precision film containing the circuit pattern used to expose photosensitive resist.
Plugged Via
Via filled with epoxy to provide flat surface for SMT component placement. Preferred over tented vias.
Polyimide
Synthetic polymer (KAPTON) forming the primary flex circuit base dielectric and coverlayer.
Pre-preg
Fiberglass-reinforced epoxy adhesive bonding rigid FR-4 and flexible polyimide in rigid-flex construction.
PTH
Plated Through Hole — copper-plated drilled hole providing interlayer electrical connection.
Rigid-Flex
Hybrid circuit with rigid and flexible zones laminated as one integrated assembly.
Solder Mask
Photo-imageable dielectric coating protecting rigid zone conductors and defining solder areas.
Steel Rule Die
Precision cutting tool for singulating flex circuits from production panel.
Stiffener
Rigid material (polyimide, FR-4, aluminum) bonded to flex to support components locally.
Tented Via
Via spanned by solder mask — not desirable. Vias should be plugged or mask pulled back.
Via
Plated through hole used as interlayer connection — no component lead insertion intended.
Via Fill
Via filled with epoxy and plated over — creates flat pad for SMT directly over via.
Windowed Leads
Polyimide removed at conductor zones for high-density mass termination.
ZIF Termination
Zero Insertion Force — flex tail inserted into connector with zero force, engaging via locking mechanism.
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