Flexible Printed Circuits (FPC): Glossary

FPC - Flexible Printed Circuit

Type 1 - Single sided FPC

Type 2 - Double sided FPC with plated through holes

Type 3 - Multilayer flexible printed circuit with 3 or more layers and plated through holes

Type 4 - Rigidflex multilayer printed circuit with 3 or more layers and plated through holes

Type 5 - Flexible of rigid flex printed wiring with 3 or more layers but without plated through holes

Basefilm - Metal clad dielectric film on which conductive patterns are etched

ED Copper - Electro-deposited copper (suitable for most flex to install applications)

RA Copper - Rolled (wrought) annealed copper (suitable for dynamic applications)

Flex to install (Use A) - An FPC capable of withstanding flexing during installation

Dynamic (Use B) - An FPC capable of with standing continuous flexing for the number of cycles specified on the master drawing

Class 1 - General electronic products

Class 2 - Dedicated service electronic

Class 3 - High reliability electronic products

Conductor(or sometimes called trace or track) - A conductive path that carries electrical current from one point to another

Track and gap (sometimes called trace and space) – Usually refers to the minimum conductor line width and the minimum space between conductors on a circuit or circuit design

Coverlayer - An adhesive coated dielectric film that is laminated over the conductive traces for protection and to dictate component attachment locations

Soldermask - A liquid dielectric coating that is applied over the conductive traces (often by screen printing) for protection and to dictate component attachment locations.

LPI Soldermask - A liquid photoimagable dielectric coating that is applied in a solid block over all conductive features. It is subsequently photo imaged and develop to create component attachment locations.

Annular ring - The exposed (solderable) copper ring created when a soldermask or coverlay opening is registered to a circuit plated through hole

Stiffener - A selectively placed reinforcing layer usually rigid material or dielectric film material to add mechanical strength where required (i.e to support components or connectors)

Baseplate - Usually referring to a metal layer that is adhered to the bottom of the FPC to promote heat dissipation from the attached components

PSA - Pressure sensitive adhesive, often used to attach stiffeners to FPC’s

Thermal Adhesive - a type of adhesive that requires temperature and pressure in a lamination press, often used to attach stiffeners to FPC’s

ENIG - Electroless Ni / Immersion Au, referring to a protective surface finish that preserves the solderability of copper pads (prior to solder assembly of components) or provides a matching contact surface to a connector into which the FPC may be plugged

OSP - Organic Solderability Preserver referring to a protective surface finish that preserves solderability for up to 6 months of shelf life prior to populating components by solder reflow

Cu - Copper, referring to the base copper of an FFC

Sn - Tin, referring to tin plating as a solderable surface finish on bare copper

Ni - Nickel, referring to an electroplated or electroless deposit usually be beneath a layer of plated gold

Au - Gold, referring to electroplated or electroless gold usually over nickel

Ag - Silver, often used as a silver conductive polymer ink for creating EMI shields

Pd - Palladium, sometimes used as en electroplated layer in the production of SmartCards

Ca - Carbon, sometimes used for switch contact pads, or for printed resistor or variable resistors

Stack-up - A cross-sectional diagram depicting the individual layers and their thickness in a circuit construction. This is often shown on the fabrication drawing.

EMI - Electro-magnetic interference

EMC - Electro-magnetic compliance

Pb Free - Lead free, usually referring to the solder or solder paste for attaching components

SMT - Surface mount technology, referring to components that are placed on pads coated with solder paste and subsequently passed through a reflow oven to fuse the solder and create a permanent electrical contact between FPC and component

COF - Chip on flex, a way of packaging a bare semiconductor die on a small FPC to create a 'fan out' of the very small features of the semiconductor and the larger features of a printed circuit board to which it will be attached

TAB - Tape automated bonding, a way of producing FPC's in a continuous process on a narrow reel (often like 35 mm movie reel)

R2R - roll-to-roll, a way of manufacturing FPC’s in a continuous roll format sometimes up to 500 mm wide