Electronics tutorial

Flex PCB Specific Terms and Definitions

Flex PCB are one of the best things you can buy when you have a specific engineering project. Having a basic understanding of flex PCBs is essential to collaborate with them. There is a lot of documentation on Flex PCBs that can help you figure out how to work with them. However, to read this document and understand it, you must know about specific terms and definitions surrounding the topic of flex PCBs. 

Once you know what the documentation refers to,assembling a circuit with a flex PCB will be easier. In the article below, we will help you identify the flex PCB-specific terms and definitions. 

Glossary of Terms for Flex PCB


Access Hole: The access hole helps connect to a conductive layer present in the flexible or dielectric material in a flex PCB so that the circuit can be complete. 

Activating: Chemical treatment that permits laminates of non-conducting materials to receive electroless coating. The process is often called seeding, catalyzing, and sensitizing. 

Active Components: Active components are any circuit component dependent on the circuit to receive current. Examples include components like rectifiers, transistors, capacitors, etc. 

Adhesions: The bond created between an adhesive layer of the flex circuit and another surface. 

Additive Process: It’s a process involving designing printed circuit boards where boards are made by adding material layer by layer instead of carving or etching material out. A Flex PCB may be made using an additive process.

ALIVH: The full form is Any Layer Inner Via A Hole, a technology common in the production of multilayer PCBs. The method refers to solder between the many layers of PCBs, creating an electrical connection between the layers. The ALIVH can replace traditional vias and helps with the production of high-density BUM PCBs. 

Analytical Services Lab: This lab helps with the testing capabilities of your designed PCB. Different tests include plating thickness, x-rays or images of the board or flex PCB, and inner layer connections. 

Annular Ring: The ring of copper or conductive material in the middle of a hole. 

Anode: It is the positive electrode in an electroplating system coupled with the power supply. The anodes allow for electroplating and hasten the metal towards the substance to be coated. 

Aperture: A categorized shape with an x position and y position can also appear in the aperture list. The aperture index is represented with a D-code. 

Array: A band of elements and circuits all connected in rows and columns on a board or flex PCB.

Artwork: Properly scaled photograph with an aspect ratio of 1:1 that can help the production of the conductor pattern. 

Assembly Drawing: Drawing that details the components’ placement and the designators’ reference on the printed circuit boards. Often also called a component locator design. 

Auto-CAD: Software for designing flex PCBs and saving design in .dxf format for conversion to Gerber and PCB production processes.

Automatic Optical Inspection:

Special computerized software to locate shorts or holes in the circuit boards. If there are any issues with the soldering performance in the PCB, then the AOI can help by capturing images of the inner layer and magnifying them. 

PCB specific terms


Back Drilling: The back-drilling is majorly applied in the production of PCBs or flex PCBs. Back drilling improves the integrity of signals by removing any obstructions through the plated holes. The obstructions aren’t necessary for working the PCBs and cause reflections and disturbances in the signals. 

Back-Planes: These are panels that are interconnected and can house the printed circuits, ICs, and other panels. The regular thickness for these planes is 0.125” and 0.300.”

BGA: The full form is a ball grid array. It’s a form of packaging for components that can help with surface mounting and placement of integrated circuits. Instead of pins, this array uses columns of balls for quick efficiencies. BGAs can help with mounting devices on flex PCBs like microprocessors or microcontrollers. 

Barrel: Wall constructed when coating a drilled aperture.

Base Copper: Layer of copper laminate which can occur on top of the flex PCBs, making it useful for connecting and creating new circuits. The copper layer clad to any side or layer of the base copper is often known as the base copper. 

Base Material: It’s an insulating layer that can house a more conductive material. In the case of a flex PCB, this material is usually flexible in nature. 

Base Laminate: Base Laminate is the same as base material. 

Bare Board: A bare board is a PCB without any components attached to it. 

Bed-Of-Nails: The method to assess printed circuit boards allows  assessing the board through placement on an array of contact pins. It can also check the engagement of any plated-through holes.

Blind Via: Blind via in a flex PCB involves a through-hole that can connect inner layers but is invisible to the external layers. 

Bill of Materials (BOM): A list of components in the assembly, such as a Printed Circuit Board. For a PCB, you may need the designators’ reference for the components you may need. A BOM helps with ordering any materials that you may need. 

Bleeding: Plated holes sometimes release the electrolytic solution through crevices or voids. 

Blister: A piece of the plate that seems swollen on the flex PCB. If the laminate layers are separated in a more rounded way between the base layer and the copper foil, then that’s a blister. 

Board: Simple term used to define the printed circuit board or flex PCB. You can also use it to refer to the substrate on top of the PCB. 

Board Vendor or Board House: The flex PCB or PCB manufacturer. 

Board Type: Helps you understand the manufacturing process for the PCB concerning volume. Two types of boards are single unit or panel PCBs. A single unit means the manufacturer can create PCBs one after another. 

Body: The middle portion of the electrical component is referred to as the body. No extremities like pins or connectors come in this category. 

Bond or Peel Strength: The amount of force required to divide the laminate layers from each other. 

Bow: The degree of uniformity of a board or flex PCB, the angle between the corners and the middle. 

Breakdown Voltage: Ionization or vaporization of a gas component occurs at this voltage. It can also lead to ruptures in the insulator or dielectric material. 

Bridging: Insulated conductors must also have a path between them. A bridging provides this conductive path. Neighboring traces present on any circuit board or flex PCB are examples of bridging. 

Buried Resistance Board: A board that has resistors built inside. The design can help with the integrity of the flex PCB as it can help with the functionality and connectivity of a PCB. 

Buried Via: It’s a plated through a hole within the many layers of a circuit without direct access. These end right in the center of the board.

Buildability: Involves meetings with the client and within the team to review the customer’s expectations versus the manufacturing requirements and capabilities. 

Bend Resistance: The ability of a material to repeatedly bend in specific parameters without any fracture to the board or flex PCB. 


C-Stage: When resin polymer is well-set and cured, you will call it the c-stage. The resin polymer is cross-linked and in a solid state. 

Cable: Another word for the term wire that can conduct heat and electricity. 

CAD CAM: Combination of the two terms CAD and CAM

CAM Files: These are files that help manufacture the flex PCBs. They have both a photo plotter and an LDI exposure unit.

CAD Files: It’s short for computer-aided design, which software designers use to design distinct aspects and layers of a flex PCB layout. The design is three-dimensional and results in CAD files. 

CAE Files: Short for computer-aided engineering, software packages that allow designers to create schematic packages that can help with the development and visualization of PCB designs. 

Carbon Mask: The mask is made of carbon toner and resin applied to the pad’s surface as a paste. These carbon masks are good for use in keys and jumpers for protection. 

Ceramic Substrate Printed Board:

Alumina or Aluminum nitride is used to bond additional materials to the ceramic substrate used to create this board. Their main selling factors are ceramic substrate boards’ superior insulating properties, heat capacity, soft weldability, and adhesion toughness.

Cap Lamination: Cap lamination is necessary for making several layers of the multiprint boards. These surfaces are often metal-clad, which helps them bond in a single operation. 

Capacitance: Electrical components that help store power and energy between them. These capacitors help with the storage of electric signals with a voltage or potential difference between them. 

Check Plots: It is a list of check items that help you take note of items for quality control for the flex PCB. 

Card-Edge Connector: It is a connector with gold plating that is built on the edge of a printed circuit board. 

COB: It also stands for chip-on-board. With this board, you don’t have to package integrated circuits; instead, you can simply mount them as you want. They are often used when you’re using flex PCBs for commercial items like gadgets or toys. There is a black glob on components which keeps it glued down. 

Chamfer: A rounded corner to prevent any issues while handling 

Characteristic Impedance: It’s a quality that helps with the overall measurement of a transmission line’s resistance, capacitance, inductance, and conductance in an ohmic value. The printed wiring value of CI is contingent on the dimensions and dielectric constant of the conductor. Along with the distance the conductor has from the ground. 

Chip Scale Package: This package will be a size within the 20% range greater or less compared to the die’s size inside it. 

Circuitry Layer:  It is the PCB layer with conductors that have both the ground plane and the voltage plane. 

Coating: The coating is a film or layer around the PCB or flex PCB and can help its decoration, protection, and insulation. 

Component: A component is any electrical device that can fit into the PCB and add to the circuit. Examples of components are capacitors, resistors, inductors, wires, and connectors. 

Clearance Hole: It is a round opening in the circuitry or the conducting layer in combination with the aperture in the printed circuit board material.

Coefficient of Thermal Expansion: A fractional change of temperature can lead to changes in the dimensions of material per the unit of temperature, which you can express as a percentage. 

Component Hole: A complete hole in the PCB or flex PCB, often used to attach and connect different components. It’s majorly used to connect one wire to another. 

Conductive Anodic Filament (CAF): An electrical short will exist within the PCBs when the manufacturer may build conductive filament within the conducting layer. There must be two conductors right next to each other for this filament with electrical bias and humidity. 

Conductor: An area in the PCB which is majorly made of copper. It has lands and paths that help with their connectivity. 

Conformal Coating: A protective coating is applied to ensure conforming to all the components on the board. 

Connector: A transmitting component that can connect one component to another component. It allows for the connection of two active components and often contains male and female parts that can be connected and disconnected. 

Controlled Impedance: It is a combination of the substrate material with trace properties so that they match and have the best possible impedance as is required in the circuit. 

Coordinate Tolerance: It allows you to create holes with proper tolerance in both linear dimensions and angular dimensions. The area creates a rectangle of variation, which is acceptable. 

Cosmetic Defect: An effect that doesn’t harm the way a flex PCB functions.

Copper Weight: This term helps to define the amount of copper in each board or the thickness of the copper foil in each flex PCB. 

Crazing: The base materials form a layer between the white splotches or cross deeper into the base layer. It displays the fibers that have splits running through the glass and resin. 

Current Carrying Capacity: A particular component may carry the most current at any time. This current doesn’t lead to any major degradation in any of the properties of the flex PCB. 


Deburring: The process of deleting copper traces that will persist around holes even after the board has been drilled. 

Delamination: Picking apart the coatings of the base material, conductive layer, and laminate. 

Destructive Testing: Partitioning a major portion of the flex PCB and investigating the section specifically under the microscope.

Dielectric Strength: The greatest voltage a dielectric material can withstand given specific conditions without undergoing any major voltage breakdowns. The value is expressed as a volt per unit of dimension. 

Dimensional Stability: It’s a quantity that measures the dimensional changes that may occur due to physical factors, including age, temperature, chemical treatment, etc. 

Dry Film: It involves a material used to make photos when exposed to UV light with a wavelength of 365 nm. The exposed UV film gets hardened by UV light, and the rest of the film can be washed away with a developer solution. 


Edge Bevel: When the edges are beveled to ensure they can easily fit into the circuit.

Dynamic Flex: A circuit capable and able to move as it works. Often used in flex PCBs.

Edge Connector: Connectors that are specifically made for the edge of a PCB and can help with the application of an Add-On Card

Edge Plating: The plating refers to copper plating even on the edges of the flex PCB or rigid PCB that allows for smoother edge connections. 

EMC: Short form for electromagnetic compatibility, it’s a value that helps measure the capability of an electric component to run without key issues with electromagnetic interference. Electromagnetic interference can cause major problems in the circuit, which is why it’s necessary for there to be a value for EMC. 

ESD: Stands for electrostatic discharge that may be present due to static electricity


Fabrication Drawing: Drawing that helps manufacture the printed circuit board. Helps show all the places where holes may be present, along with sizes, and their dimensions. These drawings have maximum information in the process of fabrication. 

Finger: A terminal with gold plating or connector for card edges. 

Fixture: A system that connects a PCB and spring-contact probe test pattern. 

Flexible Printed Board (Circuit): Involves a printed circuit board made from only flexible materials. Also called a flex PCB. 

Flying Probe Tester: It’s a machine to evaluate the fault between two connections on a board using signals sent between the two points. The procedure helps identify where a problem exists. 

Fused Coating: A coating that uses metal that may melt and helps form a better bond with the base layer material in a PCB or flex PCB. 


Gerber File: The most common type of CAM file that uses a photoplotter. One of the most common ways of communicating board specifications between fabricators. 

Grid: A rectangular network where two groups of lines are parallel and equal in distance from each other. These are often used as points for determining the location on a flex PCB. The grid can help in the transmittance of power. 

Ground Plane:  It is a point commonly employed as a reference point in the PCB for all sorts of return paths and circuit returns. 


Half-Cut: It involves holes on the board’s edge, which are also plated. These holes are mostly half-circle in shape and are common for microchip testing. 

HDI: Full form is a high-density interconnect. It uses sequential lamination and has very thin lines and dielectrics. The best kind of PCBs for prototypes.


Inner Layer: A layer that is in the interior of a multilayer board or flex PCB. 

Ink: Regular term for any screen resistance. 

Insulation Resistance: All components, conductors, and other electrical devices have some electrical resistance when it comes to their connection, and this quality measures this resistance. 


Keying Slot: This slot is in the flex PCB and is responsible for creating poles within it. The slot allows you to align with the pins and connect to the mating receptacle. You cannot then plug it into a separate or reversed receptacle. 


Land: An area with the conductive pattern spread out but not completely covered. It can help with the connection or any attachment to the component. It may also be described as a pad. 

Laser Photo Plotter: Employs a laser to expose the film from a photo plotter. 

Layer-to-Layer Spacing: Involves the space and distance between the flex PCB layers. A less amount of spacing can cause greater issues with the manufacturing process.

Lead: A terminal or a component can also be called a lead. 


Misregistration: A lack of dimensional conformity when sequential patterns are present. 


Numerical Controlled NC File: File that informs the drill about the dimensions and location of the holes. 


Overhang: Plating build-up can sometimes occur with the amount of copper in the file, or it may occur if excessive undercut occurs during the etching of a PCB or flex PCB. 


Pattern Plating: Plating the PCB or flex PCB in a specific pattern. 

Polyimide: The polymer with greater than two imide radicals in the major chain. 

Pattern Plating: Specific electrolytic plating per the conducting pattern. 

Prepreg: A plate with resin cured on it to an intermediate level. Fiberglass-reinforced epoxy adhesive bonds different layers in a rigid flex.

Photoetching: The chemical, mechanical, or otherwise removal of the portion of the conducting layer which is not wanted. 


Sequential Lamination: This process allows several layers to be formed initially and then stacked to create a complete laminate. The stacks are created by having a conductive pattern on both sides that is joined together with holes. The additional layers may then be joined to this intermediate laminate. 

Solder Leveling: Dipping a PCB into the solder and then leveling using hot air.

Static Flex: A flex PCB that has bending capabilities for proper installation. 

Stiffener Board: A piece of material that can be attached to flexible PCBs to ensure that they have more mechanical strength. 


Thermal Cure: Hardening an organic substrate layer with heat to create chemical reactions. 

Window: An aperture that allows conductors to be more open and exposed in the dielectric of a flex PCB. 

Final Thoughts

Knowing these specific terms and definitions surrounding flex PCBs can make it much easier to understand how to create circuits using these boards. Flex PCBs are a new printed circuit board, so you must gain all the information possible before you start doing projects. These boards can be expensive, so if you misunderstand anything that a manufacturer may be telling you, it may cost you a lot of time and money to start again. 

The specific terms and definitions can also help broaden your understanding of circuitry, which can help you make better choices when selecting between standard PCBs and flex PCB. 

If you still need to learn about flex PCB or HDI PCB, or you want to know more about the specific terms and definitions.


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