This glossary is designed to provide some quick definitions to terms commonly used in the design and fabrication of printed circuit boards. It’s a growing list that we contribute to frequently so we hope you will find it useful!
Automated Optical Inspection (AOI)
AOI is used to inspect the inner layers of a multi-layer PCB prior to laminating the layers together. The optics along with the board data are used to find possible shorts or opens in the copper features that will prevent problems once the inner layers are laminated together. Read more about AOI here.
The annular ring is a round copper area surrounding a drilled hole. The ring (also called a pad) allows an electrical connection from a connecting trace through the hole to other connecting traces either on an inner layer or the other outside layer.
Acceptance Quality Level (AQL)
On any given production run of printed circuit boards there is an acceptable amount of defective boards, also known as AQL. These are removed during the test and inspection process. The level is closely monitored to ensure processes are meeting consistent quality requirements.
An array combines a single PCB multiple times to make a larger array of connected boards; or a “matrix” so to speak. This process is referred to as “stepping out” the individual boards and also often referred to as “step and repeat.” Other terms used to describe an array include: panelized, stepped out, palletized and rout and retain. An array is used to make the assembly process faster.
Array # Up
This term is used to designate how many individual PCBs are on an array.
Rails are extra PCB material that are added to the sides of an array to allow for easier handling during the assembly process. The rails could be on all four sides of the array or only on two sides.
Array X Dimension
This is the dimension of an array of PCBs across the x-Axis (left to right).
Array Y Dimension
This is the dimension of an array of PCBs across the y-Axis (up and down).
In PCB manufacturing the artwork is the electronic data (see CAM Data) that is used to produce the artwork master. This data is usually scaled and not a 1:1 representation. Please review our article about Common Problems with Gerber Files
When the artwork is sent to the plotter it creates a photo image that is a 1:1 scale of the circuit that will be used in manufacturing. From there the image can then be applied to the copper clad laminate to start the manufacturing process.
Also called Prepreg. The condition of the fiberglass material used on multi-layer PCBs that is placed between the core layers of the board. It is still pliable and soft until it is heated and pressed in a lamination press. The heat causes the material to “flow” and then it will harden as it cools.
A completed printed circuit board prior to any components being placed on it.
A drilled hole can be either plated or unplated. The walls of a plated hole are called the hole barrel. This creates a connection between the top of the board, the inner layers (if present) and the bottom of the board.
Bed of Nails
A Bed of Nails is used as part of an Electrical Test for a PCB. A frame is made that will hold test pins that match up with the connection points on the circuit board. An electrical charge is applied to check for opens and shorts to provide a pass or fail for the board. This method is not used very often; Flying Probe is the typical test method.
A beveled edge is typically used to make the leading edge of a circuit board more pointed so that it can be inserted into a connecting device. The standard is a 30 degree bevel. An example would be a PCI card that is inserted into a PCI slot in a PC.
Black pad can happen on PCBs that have an Immersion Gold Finish (ENIG). It is a condition where a surface mount component soldered to a PCB loses connection. The nickel under the gold becomes corroded and creates a break in the connection.
Blind Vias are used in multi-layer boards where a drilled hole needs a connection from an outer layer to an inner layer where the hole must stop before the opposite outer layer.
A blister will appear in a localized section of the board when a separation between either the board material or between the material and any copper foil occurs. This may or may not cause a failure in the board depending on the location and is considered a form of delamination.
Usually referring to the final thickness of the printed circuit board. This would include the fiberglass, soldermask and silkscreen and the board finish. The most commonly used thickness is 0.062″ but many options are available.
Body Gold indicates that the full body of the board is plated gold. This may occur during either electro plating or immersion depending on the design.
Printed circuit boards are manufactured on a larger panel and then individually routed out. That production panel has a border area in order to allow for tooling holes and room for mounting to equipment during the manufacturing process. Typically that boarder area is one inch on all sides.
Bow references the flatness of a printed circuit board. In the case of a bow all four corners of the board would be able to touch a flat surface equally but the middle area of the board would not be touching.
Buried Vias are used in multi-layer boards where inner layers need a connection but the drilled hole is on the inner layers only and does not extend to the outer layers.
When drilling a PCB there is often a ridge or piece of material that is left connected to the drilled hole. The burr will need to be removed to not cause any problems in the rest of the manufacturing process.
(See also B-Stage Resin) This is the final hardened stage of the resin used during the lamination process of the multi-layer PCB.
CAD (Computer Aided Design)
CAD refers to the software used by a PCB designer to create the files and needed data that is used to manufacture and assemble the circuit board and components.
CAM (Computer Aided Manufacturing)
CAM refers to the software used by PCB manufacturers to prepare customers engineering files (See Gerber Files Blog Post) for the final manufacturing process.
These are the files that provide the needed information for the manufacturing of the printed circuit board.
The ability to store energy in an electrostatic field. In relation to the impedance of a circuit board it is the relationship between dielectrics and the location and size of conductors. To learn more see our article on Controlled Impedance
When a hole is drilled at the edge of the board and plated, leaving an open half circle at the edge of the board. This is often used in a board design for a circuit that will be used to test microchips.
Check Plots are typically a PDF file that depicts the Gerber files once they have been through the CAM process. The plots can be reviewed by the customer to make sure that the data is correct and ready for manufacturing.
Clad references the material used in manufacturing PCBs. Fiberglass material is “clad” with copper and is used as the starting place for manufacturing of the PCB.
For commercial PCBs this is the highest standard for manufacturing for high reliability circuits that would be used in flight controls or for some type of life support function.
A clearance (also called isolation) is space used to create a separation from a power or ground layer near a plated hole on an inner layer. A clearance will prevent a short from the plated hole to either the power or ground plane.
Coefficient of Thermal Expansion (CTE)
A measurement of the amount the PCB material will change per degree of temperature. This is a key factor in when determining which material is the best one to use for a given circuit design. Material manufacturers will provide these details in their material specifications sheet. You can find these for many material in our Materials Library
Comparative Tracking Index (CTI)
Is used to measure the electrical breakdown properties of the insulating material used in PCBs. It is primarily used to assess electrical safety especially for human users of electrical devices. Material manufacturers will provide these details in their material specifications sheet. You can find these for many material in our Materials Library
A plated hole on the circuit board that is intended to have a component pin placed in it. This could include the component pin, terminations or wires. It is good to designate if a hole is a component hole or not because the size of a component hole is more critical than a hole that will not have a component placed in it.
This is typically the top side of the circuit board. Most often is labeled in the data files as component side, layer 1 or top side. It is important when submitting your files that the component side of the board is clearly labeled to ensure the CAM and manufacturing process is done correctly.
This is the pattern of the copper on the final circuit board. This would include the traces, pads, etc. that make up the circuit on the board.
Computer Numerical Control (CNC)
Refers to the computer control that is used with modern day machinery. It is most often used in the PCB manufacturing process with CNC Drill Machines as well as Rout machines that cut the individual boards away from the production panels.
The space between the copper traces on a PCB. Spacing may vary greatly on any individual board. Typical minimum spacing would be 0.007″ but could go down to extremes of 0.003″.
The thickness of the copper traces on a PCB. The most common thickness would be 1oz or 0.014″. 1oz refers to the amount of copper that would cover one square foot area.
A coating that is added over the printed circuit board and the installed components on the circuit board in order to provide protection to the circuitry. The protection could be against weather, water, dirt, etc.
Refers to the uninterrupted flow of the electrical current in a circuit. Most often referred to as a part of the electrical test of a circuit. To learn more see our article on Bare Printed Circuit Board Electrical Test
Adjusting the thickness of the circuit boards materials (fiberglass) in order to create a specific electrical effect. Most often used in multi-layer boards in order to obtain the desired impedance. Please see our post on Controlled Impedance
for further details.
Electrical impedance is the measure of the opposition (resistance) that a circuit presents to the passage of a current when a voltage is applied in an alternating current circuit. Controlled Impedance is the process of manufacturing a PCB to meet a specific impedance requirement. See our more detailed article on Controlled Impedance
The Copper Weight (also called Finished Copper Weight) is the total thickness of copper on the surface of a PCB. There are several processes that effect the final copper thickness. It is measured in oz/sq ft. For example 1 oz = a thickness of 0.0012″.
A multi-layer circuit board is made up of a core, prepreg and copper foil. The core is fiberglass material that has copper clad to it and will vary in thickness depending on the number of layers and the final PCB thickness required.
A counterbore is cylindrical flat-bottom hole that enlarges another drilled hole. It is typically used when a fastener, such as a socket head cap screw, is required to sit flush with the surface of the PCB. Read more about Counterbores
A countersink is a conical hole added to a drilled hole to allow the head of a countersunk screw to sit flush with the surface of the PCB. Read more about Countersinks
A reference to a technique used in drawing to fill an area with with volume or shading. Used in some cases with larger copper areas on the PCB. Leaves the copper with voided spaces instead of being a solid area of copper.
The process of polymerizing (chemically hardening) the epoxy based soldermask and/or silkscreen using a set temperature for a specified amount of time. This ensures the mask and silk will adhere to the rest of the material. Once the mask and silk are cured on the base material they cannot be removed.
The Date Code is added to the copper or silkscreen of the PCB during the manufacturing process. The date code shows the week and year that PCB was made.
A Datum is used in PCB design files to mark the point of the axis or plane used as the origin of the PCB design.
When any copper or laminate materials in a PCB begin to separate after the boards have been manufactured.
A desktop stencil is a laser cut stencil that is used to apply solder past to surface mount component pads on a printed circuit board by hand.
The chemical process of removing drilling debris that is left in the holes of a production PCB panel after being drilled.
Dielectric refers to the fiberglass material in a PCB. The material is non-conductive and acts as an insulator for the electrical circuit in the PCB. The properties of the dielectric material can have an effect on the electrical circuit.
Double Sided PCB
A double sided PCB is the most common of all circuit boards. It has copper on the top and bottom of the board material and includes connections through plated holes.
DRC (Design Rule Checking)
A DRC is performed with CAM software to verify the continuity of all conductors and routing within the manufacturers design rules.
Electrical Test is the process of testing the board for continuity and isolation. (opens and shorts). Typically the end points of all nets are checked for opens and shorts. It does not include functionality testing of the PCB. Read more about Electrical Test
The process of depositing a conductive material from a plating source using the application of an electrical current. This is used for plating in the hole walls as well as adding plating the copper pattern.
The process of depositing a conductive material from an autocatalytic plating solution without the application of an electrical current. Used to apply a thin amount of copper prior to copper plating to improve the possible connecting in the hole walls. Is also used when applying various finishes to the board such as ENIG (Electroless Nickel Immersion Gold).
Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)
Similar to ENIG but applies palladium over the nickel prior to the application of the gold. This prevents any problems of corrosion between the nickel and gold and makes it a very “universal” surface finish. Can be used for fine pitched components as well as gold wire bonding.
Electroless Nickel Immersion Gold (ENIG)
ENIG is a very thin amount of Gold applied over Nickel. The nickel is plated onto the copper prior to the application of Gold and acts as a barrier to prevent the Gold and the Copper from migrating into one another. The gold will disappear when soldered, as it is absorbed in the process. Excellent for very fine pitched components.
The electro-deposition of metal coating on a conductive object. The metal may be conductive or non-conductive. The object is placed in an electrolyte and connected to one terminal of a DC voltage source. The metal to be deposited is similarly immersed and connected to the other terminal. This creates a current flow from the metal to the conductive material thus depositing the material. In PCB manufacturing it is used to apply copper to the hole walls and copper conductor pattern.
Small adjustments are made to normalized Gerber data it compensate for the amount of copper that will be etched from the production panel. This can vary depending on the copper weight and is determined by the CAM operator based on quality controls.
Chemically removing the sidewalls of plated through holes in order to expose conductor areas on inner layers or a multi-layer PCB.
After an image pattern as been applied to a panel of copper clad fiberglass the unwanted copper is chemically etched away.
Excellon Drill File
The data file that defines the drill hole sizes, X & Y coordinates, and tool numbers for a circuit board. Also called a NC (numerically controlled) drill file.
A drawing that is used to provide additional information for the correct manufacturing of the PCB. It may include the location of holes, sizes and tolerances, board dimensions, material to be used, finish choice and any other important information not included in the gerber files.
The fiducial is a circle that is a copper pad with the same finish as the rest of the board and provides alignment targets for automated assembly equipment. A fiducial may be on the rails of the array, on individual boards or next to special components. Typically three fiducials are needed on an array and the ideal size is 0.050”.
A first article is a test run of a particular manufacturing process. It is useful to verify that all manufacturing parameters are correctly in place. For example when routing PCBs away from a production panel a single board will be routed out first to verify the rout program is correct.
Flash gold is hard gold with a maximum thickness of 3 micro inches. It is very thin and requires special handling.
This is an electrical test method of bare circuit boards. The flying probe machine uses several arms with probes on the end that work together to touch the test points on the circuit board to determine if there are any opens or shorts on the board.
Fixed Frame Stencil
A fixed frame stencil is a laser cut stencil that is permanently attached to an aluminum frame.
FR-4 is fiberglass material that has a specific standard for flammability. It is the most common material used in the manufacturing of printed circuit boards.
A laser cut stencil that will be placed inside a universal frame. A frameless stencil will have holes cutout along the each edge of the stencil so that it can be attached to a universal frame.
Gold Fingers are gold plated connectors on an edge of the PCB. The hard gold plating allows for the PCB to be inserted into a connector without damaging the surface of the connections. Read more about Gold Fingers here
In PCBs this is a conductive area of the board, often an entire layer, that is usually connected to the power supply ground of the circuit.
Hard Gold is an electrolytic process and has hardeners in it for durability. It is plated over a nickel finish and may also be referred to as Deep Gold. (The term Deep Gold is used to indicate that full panels are placed in the plating tank prior to the application of soldermask.)
HASL, Hot Air Solder Level is a common finish type for PCBs. The PCB panel with exposed copper is lowered into a liquid bath of solder then quickly raised out of the bath and moved passed jets of hot air that clear off the excess solder leaving only the solder on the exposed copper areas.
Home Base Apertures
Home base apertures are the shape of the aperture used in laser cut stencils that will control solder balling and tomb-stoning of chip components.
The process of taking the electronic data of the circuit patterns and transferring that data to the photo plotter or image device to apply the image to the film.
A plating process that does not use electroplating to transfer various metals to the copper base of a PCB. Most commonly used to apply Gold or Silver in an immersion process.
The purpose of this silver plating is to protect the copper from corroding as well maintaining its solderability. It does have a shorter shelf life than some other finishes and must be shipped with separator sheets to prevent tarnishing.
Commonly referred to as White Tin, Immersion Tin is a chemical process which applies a very thin layer of tin to the copper. The appearance is mostly white, has a shorter shelf life and is good for tight pitched components. Read more about Immersion Tin here
Electrical impedance is the measure of the opposition (resistance) that a circuit presents to the passage of a current when a voltage is applied in an alternating current circuit. To learn more see our article on Controlled Impedance
For printed circuit boards the standard and guidelines that are followed are published by the IPC Association (See IPC). The primary criteria is based on the document titled “IPC-A-600” which provided the necessary guidelines for the acceptability for printed circuit boards for Classes 1 to 3.
Institute for Interconnecting and Packaging Electronic Circuits (IPC)
Primary industry governing body and often, the final authority on how to design and manufacture printed circuit boards.
Refers to the fiberglass material used in a PCB. Typically in reference to a multi-layer circuit board.
The thickness of the fiberglass material before the soldermask, silkscreen or finishes have been applied to the PCB.
A space that opens inside the fiberglass material of a PCB that can be seen with a visual inspection.
The land or pad is the copper area that is designated for the mounting of components to the circuit board.
Laser Photo Plotter
As opposed to a vector plotter, a laser plotter is able to produce very fine lines and dots to create a more accurate photo plot.
Lead Free HASL
Similar in appearance and use as Leaded Solder with Hot Air Solder Level. Contains a mix of 99.3% Tin and 0.6% Copper. It may be referred to as SN100CL. The temp at which it flows is around 515 degrees as compared to around 485 for Leaded Solder.
LPI (Liquid Photo-Imageable) Ink
LPI is an epoxy based ink that is applied to a PCB for solder mask or silkscreen through photographic imaging techniques. The PCB panel is covered in the ink then the image is exposed and developed. This method allows for a very precise thickness and accuracy for the solder mask application. Read more on Outer Layer Image and Soldermask
Note: Bay Area Circuits also uses this process for Silk Screening a PCB.
A form of delamination just below the surface of the laminate material that is visible and shows as several small circular areas.
The copper foil that is used for the conductive layers of the PCB.
Part of the quality or inspection process will often require a Micro-Section of the circuit board. A small rectangular area of the board is punched out of the board in order to inspect the quality of the hole walls and plating. It allows for a look at the inner layers of the board to verify the overall process.
This is an unplated hole (meaning it will be non-conductive) that is used to secure the circuit board to its final assembly.
Multi Layer PCB
A Multi Layer PCB is a PCB that has more than two layers. Read more about Multi-Layer PCBs
List of names of symbols or parts and their connection points which are logically connected in each net of a circuit.
Also see Legend or Silkscreen. This is applied to the circuit board to identify components and other key information on the bare circuit board.
Non Plated Hole
A Non-Plated hole is a hole that is drilled after the copper plating process so that there is no plating in the hole. Often used for mounting holes.
NRE (Non-Recurring Expense)
A NRE is any type of onetime costs related to the manufacturing of a printed circuit board. These costs will vary but could include Tooling or Engineering costs, electrical test etc.
An open circuit is a break in the continuity of any given circuit on the board. This would be identified during the electrical test process which would result in a failed test.
Organic Surface Protectant (OSP)
OSP is an organic chemical finish that is applied to the copper. The shelf life is very short with OSP and the boards should be used very soon after applying the finish.
The process to electroplate only select portions of a production PCB panel.
Used to print the patterns on the photo tools used to manufacture a PCB.
Light sensitive material that is applied to the production PCB panel and then used to expose the pattern from the photoplot and developed. The remaining copper that is not covered by resist is etched away leaving only the copper pattern needed for the board.
Printed by the photo plotter to be used for making the copper pattern. Also used for making the patterns for soldermask and silkscreen.
Plasma Etching is a process used to remove copper from a PCB panel for special RF materials that cannot be processed with standard etching procedures.
A Plated Hole is a drilled hole on a PCB panel that has completed a plating process to allow a copper connection with pads connected to the hole.
The reference designator is generated from the Gerber data to provided additional data when loading components on the printed circuit board. It defines the component and its placement on the board.
A laser cut stencil used when a single component needs to be re-worked when the rest of the components are already soldered to the printed circuit board.
Rout is the process of using a programmed rout machine to cut a PCB out of the manufacturing panel.
A schematic is created as the first step of a PCB design. It includes graphic symbols of the electrical connections and functions of the circuit board.
Selective Gold indicates that a specific area in the interior of the board would be plated. This does not include gold fingers.
Refers to a short circuit in the circuit board. A short could have been accidentally created in the design of the board or is a result of an error in the manufacturing process. An electrical test can be used to identify the short to prevent it from passing final inspection.
Single Layer PC
A Single Layer PCB is a PCB with copper features on only one side of the material of the board.
SMT Laser Cut Stencil
Used to apply solder paste to a printed circuit board to aid in the soldering of surface mount components. The stencil is usually stainless steel and can be used many times in the electronics assembly process.
Also called Solder Cream, is used to solder a surface mount component lead to a corresponding land (pad) on a printed circuit board.
The solder side is the bottom side of the PCB.
Soft gold is commonly referred to as “wire bondable gold”. It is softer than other gold finishes which allows it to be bonded to more easily for stronger and more conductive connections. The gold does not disappear at the point of soldering or wire bond which produces a stronger welded joint.
Stencil Fiducials are alignment marks. If your screen printer is equipped with a vision system, fiducials half cut in the stencil to allow for the printer to automatically align the board with the stencil. If you are manually aligning the stencil with the board, you could either full cut the fiducials or just use the surface mount pads.
The process of “stepping out” the individual boards in an array. Other terms used to describe an array are: panelized, stepped out, palletized and rout and retain.
Tab Rout is most commonly used when a single PCB is duplicated several times in an array. Tab Rout arrays will leave a small tab on all four sides of the board attached to the other boards or to rails. Read more about Arrays
TDR stands for Time Domain Reflectometer. When using Controlled Impedance in a PCB a TDR test is used to verify the specific impedance requirements as needed.
There are a variety of tolerances in the printed circuit board manufacturing process. They are most often identified in a customer’s design files as + (plus) or – (minus) amount depending on the area and process of the board. For example the overall thickness of a circuit board is typically going to be a +/- 10% of the overall thickness. In this case a board requirement of .062” would still be within tolerance if the thickness was .068″.
Tooling holes are commonly used in four corners of the rails of a PCB array. They are used to aid in alignment and orientation when assembling the board. The typical size is .125” and they are non-plated.
In laser cut stencils Trapezoidal Apertures are created by distorting the beam on the laser, creating a draft in the aperture wall. Trapezoidal Apertures are effective if you plan on a long dwell time between printing of solder paste and placement of components. The taper in the aperture wall causes the paste to sit on top of itself, rather than sliding out the sides.
Twist references the flatness of a printed circuit board where not all four corners of the board are able to touch at the same time on a flat plane.
Universal Frame Stencil
A universal frame provides a solid frame to connect a frameless stencil.
A V-Score is a small grove that is cut into an array of PCBs so that after components are added they can easily be separated. Read more about Arrays
Wire Bondable Gold
Wire bondable gold also called soft gold. It is softer than other gold finishes which allows it to be bonded to more easily for stronger and more conductive and stronger connections. It is 99.99% pure – 24 carat gold with a typical thickness of 30 to 50 micro inches of gold.
An X-Out occurs when on an array of PCBs a single board fails electrical test or final inspection and are “X’ed out” with a marker to designate that they are not to be used. Some customers or end users specify a percentage of X-Outs allowed while others require that there be no X-Outs in an array. This should be specified when quoting the PCBs because additional costs may be incurred.
The x-Axis is the horizontal (left and right) axis of a two-dimensional plot.
The y-Axis is the vertical (up and down) axis of a two-dimensional plot.
Where the xy-plane is horizontal then Z-axis would point up from the point where x and y meet.
A .zip file is a compressed file that contains the needed design files for the manufacturing of a printed circuit board. As an example for a two layer board the files included would be Gerber files for the Top Copper, Bottom Copper, Top Soldermask, Bottom Soldermask and Top Silkscreen. It would also include the NC Drill file and a Fabrication Drawing.