Our Printed Circuit Board (PCB) Glossary is a list we have complied to offer definitions to some of the words and phrases you will often read and hear while working with circuit boards. Some of the term definitions below were adapted from the publication we highly recommend, “Printed Circuits Handbook”, by Clyde F. Coombs.
ACCELERATOR: A chemical that is used to speed up a reaction or cure, as cobalt napththenate is used to accelerate the reaction of certain polyester resins. It is often used along with a catalyst, hardener, or curing agent. The term “accelerator” is often used interchangeably with the term “promoter.”
ACCURACY: The ability to place the hole at the targeted location.
ADDITIVE PROCESS: A process for obtaining conductive patterns by the selective deposition of conductive material on an unclad base material.
ADHESIVE: Broadly, any substance used in promoting and maintaining a bond between two materials.
AGING: The change in properties of a material with time under specific conditions.
ANNULAR RING: The circular strip of conductive material that completely surrounds a hole.
ARC RESISTANCE: Test technique using a low current arc placed above the surface of the material. Arc resistance describes the material resist tracking or forming a conductive path.
ARTWORK MASTER: An accurately scaled configuration used to produce the production master.
BACKUP MATERIAL: A material placed on the bottom of a laminate stack in which the drill terminates its drilling stroke.
BASE MATERIAL: The insulating material upon which the printed wiring pattern may be formed.
BASE MATERIAL THICKNESS: The thickness of the base material excluding metal foil cladding or material deposited on the surface.
BLIND VIA: Conductive surface hole that connects an outer layer with an inner layer of a multilayer PWB without penetrating the entire board.
BLISTERING: Localized swelling and separation between any of the layers of the base laminate or between the laminate and the metal cladding.
BONDING LAYER: An adhesive layer used in bonding other discrete layers during lamination.
BOND STRENGTH: The force per unit area required to separate two adjacent layers by a force perpendicular to the board surface; usually refers to the interface between copper and base material.
BOW: A laminate defect in which deviation from planarity results in a smooth arc.
B-STAGE: An intermediate stage in the curing of a thermosetting resin. In it a resin can be heated and caused to flow, thereby allowing final curing in the desired shape.
B-STAGE LOT: The product from a single mix of B-stage ingredients.
B-STAGE RESIN: A resin in an intermediate stage of a thermosetting reaction. The material softens when heated and swells when in contact with certain liquids, but it may not entirely fuse or dissolve.
BURIED VIA: Conductive surface hole that connects one inner layer to another inner layer of a multilayer PWB without having a direct connection to either the top or bottom surface layer.
BURR: A ridge left on the outside copper surfaces after drilling.
CAPACITANCE: The property of a system of conductors and dielectrics which permits the storage of electricity when potential difference exists between the conductors.
CAPACITIVE COUPLING: The electrical interaction between two conductors caused by the capacitance between the conductors.
CARBIDE: Tungsten carbide, formula WC. The hard, refractory material forming the drill bits used in PWB drillings.
CATALYST: A chemical that causes or speeds up the cure of a resin but does not become a chemical part of the final product.
CERAMIC LEADED CHIP CARRIER (CLCC): A chip carrier made from ceramic (usually a 90-96% alumina or beryllia base) and with compliant leads for terminations.
CHIP CARRIER (CC): An integrated circuit package, usually square, with a chip cavity in the center, its connections are usually on all four sides. (See leaded chip carrier and leadless chip carrier.)
CHIP LOAD (CL): The movement of the drill downward per revolution; usually given in mils (thousandths of an inch) per revolution.
CHLORINATED HYDROCARBON: An organic compound having chlorine atoms in its chemical structure. Trichloroethylene, methyl chloroform, and methylene chloride are chlorinated hydrocarbons.
CIRCUIT: The interconnection of a number of electrical devices in one or more closed paths to perform a desired electrical or electronic function.
CLAD: A condition of the base material, to which a relatively thin layer or sheet of metal foil (cladding) has been bonded on one or both of its sides. The result is called a metal-clad base material.
CNC: Computer numerically controlled. Refers to a machine with a computer which stores the numerical information about location, drill size, and machine parameters, regulating the machine to carry out that information.
COAT: To cover with a finishing, protecting, or enclosing layer of any compound.
COLD FLOW: The continuing dimensional change that follows initial instantaneous deformation in a nonrigid material under static load, also called creep.
COLLIMATION: The degree of parallelism of light rays from a given source. A light source with good collimation produces parallel light rays, whereas a poor light source produces divergent, nonparallel light rays.
COMPONENT HOLE: A hole used for the attachment and electrical connection of a component termination, including pin or wire, to the printed board.
COMPONENT SIDE: The side of the printed board on which most of the components will be mounted.
COMPOUND: A combination of elements in a stable molecular arrangement.
CONDUCTIVE FOIL: The conductive material that covers one side or both sides of the base material and is intended for forming the conductive pattern.
CONDUCTIVE PATTERN: The configuration or design of the electrically conductive material on the base material.
CONDUCTOR LAYER 1: The first layer having a conductive pattern, of a multilayer board on or adjacent to the component side of the boards.
CONDUCTOR SPACING: The distance between adjacent edges (not centerline to centerline) of conductors on a single layer of a printed board.
CONDUCTOR THICKNESS: The thickness of the copper conductor exclusive of coating or other metals.
CONDUCTOR WIDTH: The width of the conductor viewed from vertically above, that is, perpendicularly to the printed board.
CONFORMAL COATING: An insulating protective coating which confirms to the configuration of the object coated and is applied on the completed printed board assembly.
CONNECTOR AREA: The portion of the printed board that is used for providing external (input-output) electrical connections.
CONTACT BONDING ADHESIVE: An adhesive (particularly of the nonvulcanizing natural rubber type) that bonds to itself on contact, although solvent evaporation has left it dry to the touch.
CONTROLED IMPEDANCE: The matching of substrate material properties with trace dimension and locations to create specific electric impedance as seen by a signal on the trace.
COPOLYMER: See polymer.
CORE MATERIAL: The fully cured inner-layered segments, with circuiting on one or both sides that form the multilayer circuit.
CORNER MARKS: The marks at the corners of printed boards artwork, the inside edges of which usually locate the borders and establish the contour of the board.
COUPON: One of the patterns of the quality conformance test circuitry area. (See test coupon)
CRAZING: A base material condition in which connected white spots or crosses appear on or below the surface of the base material. They are due to the separation of fibers in the glass cloth and connecting weave intersections.
CROSS-LINKING: The forming of chemical links between reactive atoms in the molecular chain of a plastic. It is cross-linking in the thermosetting resins that makes the resins infusible.
CROSS TALK: Undesirable electrical interference caused by the coupling of energy between signal paths.
CRYSTALLINE MELTING POINT: The temperature at which the crystalline structure in a material is broken down.
CTE: Coefficient of thermal expansion. The rate of thermal expansion is a function of the components used in the base material and their relative concentrations. The resin system will have a relatively high coefficient of thermal expansion compared to fiberglass cloth or other types of inorganic reinforcements. Improved materials have reduced levels of thermal expansion.
CTI: Comparative Tracking Index. Indicates the highest usable voltage for that laminate. It becomes important in application with high humidity, such as washing machines or cars. A higher index means a better protection. Similar is ‘PTI’ and ‘KC’.
CURE: To change the physical properties of a material (usually from a liquid to a solid) by chemical reaction or by the action of heat and catalysts, alone of in combination, with or without pressure.
CURING AGENT: See hardener.
CURING TEMPERATURE: The temperature at which a material is subjected to curing.
CURING TIME: In the molding of thermosetting plastic, the time in which the material is properly cured.
CURRENT-CARRYING CAPACITY: Maximum current which can be carried continuously without causing objectionable degradation of electrical or mechanical properties of the printed board.
DATUM REFERENCE: A defined point, line, or plane used to locate the pattern or layer of a printed board for manufacturing and/or inspection purposes.
DEBRIS: A mechanically bonded deposit of copper to substrate hole surfaces.
DEBRIS PACK: Debris deposited in cavities or voids in the resin.
DEFINITION: The fidelity of reproduction of the printed board conductive pattern relative to the production master.
DELAMINATION: A separation between any of the layers of the base laminate or between the laminate and the metal cladding originating from or extending to the edges of a hole or edge of the board.
DIELECTRIC CONSTANT: The property of a dielectric which determines the electrostatic energy stored per unit volume for a unit potential gradient.
DIELECTRIC LOSS: Electric energy transformed into heat in a dielectric subjected to a changing electric field.
DIELECTRIC LOSS ANGLE: The difference between 90° and the dielectric phase angle. Also called the dielectric phase difference.
DIELECTRIC LOSS FACTOR: The product of dielectric constant and the tangent of dielectric loss angle for a material.
DIELECTRIC PHASE ANGLE: The angular difference in phase between the sinusoidal alternating potential difference applied to a dielectric and the component of the resulting alternating current having the same period as the potential difference.
DIELECTRIC POWER FACTOR: The cosine of the dielectric phase angle (or sine of the dielectric loss angle).
DIELECTRIC STRENGTH: The voltage that an insulating material can withstand before breakdown occurs, usually expressed as a voltage gradient (such as volts per mil).
DIMENSIONAL STABILITY: Freedom from distortion by such factors as temperature changes, humidity changes, age, handling, and stress.
DIRECT IMAGING: The exposure of photo resist material with a laser without the use of positive or negative photo tool.
DISSIPATION FACTOR: The tangent of the loss angle of the insulating material. Also called loss tangent or approximate power factor.
Dk: Dielectric constant; permittivity.
DRILL FACET: The surface formed by the primary and secondary relief angles of a drill tip.
DRILL WANDER: The sum of accuracy and precision deviations from the targeted location of the hole.
DSC: Differential Scanning Calorimetry. Method to measure heat flow versus temperature rather than dimensional changes by DMA.
DUMMY: A cathode with a large area used in a low current density pulsating operation for the removal of metallic impurities from solution. The process is called “dummying.”
DWELL POINT: The bottom of the drilling stroke before the drill bit ascends.
EDGE-BOARD CONTACTS: A series of contacts printed on or near an edge of a printed board and intended for mating with a one-part edge connector.
EDX: Energy dispersive x-ray fluorescent spectrometer.
ELASTOMER: A material which at room temperature stretches under low stress to at least twice its length but snaps back to its original length upon release of the stress. Rubber is a natural elastomer.
ELECTRIC STRENGTH: The maximum potential gradient that a material can withstand without rupture. It is a function of the thickness of the material and the method and conditions of test. Also called dielectric strength or disruptive gradient.
ELECTROLESS PLATING: The controlled autocatalytic reduction of a metal ion on certain catalytic surfaces.
EMULSION SIDE: The side of the film or glass on which the photographic image is present.
ENTRY MATERIAL: A material placed on top of a laminate stack.
EPOXY SMEAR: Epoxy resin which has been deposited on edges of copper in holes during drilling either as a uniform coating or as scattered patches. It is undesirable because it can electrically isolate the conductive layers from the plated-through-hole interconnections.
ETCHBACK: The controlled removal of all the components of the base material by a chemical process acting on the sidewalls of plated-through holes to expose additional internal conductor areas.
ETCH FACTOR: The ratio of the depth of etch to lateral etch.
EXOTHERM: A characteristic curve which shows heat of reaction of a resin during cure (temperature) versus time. The peak exotherm is the maximum temperature on the curve.
EXOTHERMIC REACTION: A chemical reaction in which heat is given off.
FIBER EXPOSURE: A condition in which glass cloth fibers are exposed on machined or abraded areas.
FILLER: A material, usually inert, added to a plastic to reduce cost or modify physical properties.
FILM ADHESIVE: A thin layer of dried adhesive. Also, a class of adhesives provided in dry-film form with or without reinforcing fabric and cured by heat and pressure.
FLEXURAL MODULUS: The ratio, within the elastic limit, of stress to corresponding strain. It is calculated by drawing a tangent to the steepest initial straight-line portion of the load deformation curve and using the equation EB=L3m/4bd3, where EB is the modulus, L is the span (in inches), m is the slope of the tangent, b is the width of beam tested and d is the depth of the beam.
FLEXURAL STRENGTH: The strength of a material subjected to bending. It is expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure.
FLUOROCARBON: An organic compound having fluorine atoms in its chemical structure, an inclusion that usually lends stability to plastics. Teflon* is a fluorocarbon.
GEL: The soft, rubbery mass that is formed as a thermosetting resin goes from a fluid to an infusible solid. It is an intermediate state in a curing reaction, and a stage in which the resin is mechanically very weak.
GEL POINT: The point at which gelation begins.
GLASS TRANSITION POINT: The temperature at which a material loses properties and becomes a semi liquid.
GLASS TRANSITION TEMPERATURE: The temperature at which epoxy, for example, softens and begins to expand independently of the glass fabric expansion rate, usually symbolized at Tg.
GLUE-LINE THICKNESS: Thickness of the fully dried adhesive layer.
GRID: An orthogonal network of two sets of parallel lines for positioning features on a printed board.
GROUND PLANE: A conducting surface used as a common reference point for circuit returns, shielding or heat sinking.
GULL WING LEAD: A surface mounted device lead which flares outward from the device body
HALOING: A light area around holes or other machined areas on or below the surface of the base laminate.
HARDENER: A chemical added to a thermosetting resin for the purpose of causing curing or hardening. A hardener, such as an amine or acid anhydride for an epoxy resin, is a part of the chemical reaction and a part of the chemical composition of the cured resin. The terms “hardener” and “curing agent” are used interchangeably.
HEAT-DISTORTION POINT: The temperature at which a standard test bar (ASTM D 648) deflects 0.010 in under a stated load of either 66 or 264 psi.
HIGH-DENSITY INTERCONNECT (HDI): Ultra fine-geometry multilayer PWB constructed with conductive surface Microvia connections between layers. (Microvia is usually defined as a hole with a diameter less than 0.006 in.) These boards also usually include buried and/or blind vias and are made by sequential build-up lamination.
HOLE PULL STRENGTH: The force, in pounds, necessary to rupture a plated-through hole or its surface terminal pads when loaded or pulled in the direction of the axis of the hole. The pull is usually applied to a wire soldered in the hole, and the rate of pull is given in inches per minute.
HOOK: A geometric drill bit defect of the cutting edges.
HOT-MELT ADHESIVE: A thermoplastic adhesive compound, usually solid at room temperature, which is heated to fluid state for application.
HYDROCARBON: An organic compound containing only carbon and hydrogen atoms in its chemical structure.
HYDROLYSIS: The chemical decomposition of a substance involving the addition of water.
HYGROSCOPIC: Tending to absorb moisture.
I-LEAD: A surface mounted device lead which is formed such that the end of the lead contacts the board land pattern at a 90° angle. Also called a butt joint.
IMPREGNATE: To force resin into every interstice of a part, as of a cloth for laminating.
INHIBITOR: A chemical that is added to a resin to slow down the curing reaction and is normally added to prolong the storage life of a thermosetting resin.
INORGANIC CHEMICALS: Chemicals whose molecular structures are based on other than carbon atoms.
INSULATION RESISTANCE: The electrical resistance of the insulating material between any pair of contacts, conductors, or grounding devices in various combinations.
INTERNAL LAYER: A conductive pattern contained entirely within a multilayer board. IPC: Institute for Interconnecting and Packaging Electronic Circuits. A leading printed wiring industry association that develops and distributes standards as well as other information of value to printed wiring designers, users, suppliers, and fabricators. IR: infrared heating for solder-reflow operation.
J-LEAD: A surface mounted device lead which is formed into a “J” pattern folding under the device body.
JUMPER: An electrical connection between two points on a printed board added after the printed wiring is fabricated.
KIRKENDALL VOIDS: In Cu-Au or Cu-Au-Sn systems, pores in the older joint, or at copper interfaces occur through solid-state diffusion. Copper which has a relatively high solubility and solid-state mobility in gold diffuses into the gold. Transported by grain boundry diffusion at temperatures below 150°C, and by bulk diffusion above that temperature. Au-Sn regions result along with atomic vacancies. Then lattice vacancies are in profusion. Vpods can be observed and this material depletion weakens the solder joint.
LAMINATE: The plastic material usually reinforced by glass or paper that supports the copper cladding from which circuit traces are created.
LAMINATE VOID: Absence of epoxy resin in any cross-sectional area which should normally contain epoxy resin.
LAND: See terminal area.
LANDLESS HOLE: A plated-through hole without a terminal area.
LASER PHOTOPLOTTER (Laser photo generator, or LPG): A device that exposes photosensitive material, usually a silver halide or diazo material, subsequently used as the master for creating the circuit image in production.
LAYBACK: A geometric drill bit defect of the cutting edges.
LAYER-TO-LAYER SPACING: The thickness of dielectric material between adjacent layers of conductive circuitry.
LAY-UP: The process of registering and stacking layers of a multilayer board in preparation for the laminating cycle.
LCCC: Leadless ceramic chip carrier.
LEAD-FREE: Referring to solder alloys made without lead, to conform to the requirements of the European Union directive on the Restriction of Hazard Substances (RoHS) the most important of which, to the printed circuit industry, is lead. Often used to refer to any process that is designed to be compatible with “lead-free” alloys.
LEADED CHIP CARRIER: A chip carrier (either plastic or ceramic) with compliant leads from terminations.
LEADLESS CHIP CARRIER: A chip carrier (either plastic or ceramic) with compliant leads from terminations.
LEGEND: A format of lettering or symbols on the printed board, for example, part number, component locations, or patterns.
LOOSE FIBERS: Supporting fibers in the substrate of the laminate which are not held in place by surrounding resin.
MAJOR WEAVE DIRECTION: The continuous-length direction of a roll of woven glass fabric.
MARGIN RELIEF: The area of a drill bit next to the cutting edge is removed so that it does not rub against the hole as the drill revolves.
MASTER DRAWING: A document that shows the dimensional limits or grid locations applicable to any or all parts of a printed wiring or printed circuit base. It includes the arrangement of conductive or nonconductive patterns or elements; size, type, and location of holes; and any other information necessary to characterize the complete fabricated product.
MEASLING: Discrete white spots or crosses below the surface of the base laminate that reflect a separation of fibers in the glass cloth at the weave intersection.
MICROSTRIP: A type of transmission line configuration which consists of a conductor over a parallel ground plane separated by a dielectric.
MICROVIA: Usually defined as a conductive hole with a diameter of 0.0006 in or less that connects layers of a multilayer PWB. Often used to refer to any small-geometry connecting hole the creation of which is beyond the practical capabilities of traditional mechanical drilling processes.
MINOR WEAVE DIRECTION: The width direction of a roll of woven glass fabric.
MIXED ASSEMBLY: A printed wiring assembly that combines through-hole components and surface mounted components on the same board.
MODULUS OF ELASTICITY: The ratio of stress to strain in a material that is elastically deformed.
MOISTURE RESISTANCE: The ability of a material not to absorb moisture either from air or when immersed in water.
MOUNTING HOLE: A hole used for the mechanical mounting of a printed board or for the mechanical attachment of components to a printed board.
MULTILAYER BOARD: A product consisting of layers of electrical conductors separated from each other by insulating supports and fabricated into a solid mass. Interlayer connections are used to establish continuity between various conductor patterns.
MULTIPLE-IMAGE PRODUCTION MASTER: A production master used to produce two or more products simultaneously.
NAILHEADING: A flared condition of internal conductors.
NC: Numerically controlled. Usually refers to a machine tool, in this case a drilling machine. The most basic type is one in which a mechanical guide locates the positions of the holes. NC machines are usually controlled by punched tape.
NEMA STANDARDS: Property values adopted as standard by the National Electrical Manufacturers Association.
NOBLE ELEMENTS: Elements that either do not oxidize or oxidize with difficulty; examples are gold and platinum.
OILCANNING: The movement of entry material in the z direction during drilling in concert with the movement of the pressure foot.
ORGANIC: Composed of matter originating in plant or animal life or composed of chemicals of hydrocarbon origin, either natural or synthetic.
PAD: See terminal area.
PADS ONLY: A multilayer construction with all circuit traces on inner layers and the component terminal area only on the surface of the board. This construction adds two layers but may avoid the need for a subsequent solder resist, and since inner layers usually are easier to form, this construction may lead to higher overall yields. PH:A measure of the acid or alkaline condition of a solution. A pH of 7 is neutral (distilled water); pH values below 7 represent increasing acidity as they go toward 0; and pH values above 7 represent increasing alkalinity as they go toward the maximum value of 14.
PHOTOMASTER: An accurately scaled copy of the artwork master used in the photo fabrication cycle to facilitate photo processing steps.
PHOTOPOLYMER: A polymer that changes characteristics when exposed to light of a given frequency.
PINHOLES: Small imperfections which penetrate entirely through the conductor.
PINK RING: The appearance of a halo of copper around the hole of a multilayer.
PWB PITS: Small imperfections which do not penetrate entirely through the printed circuit.
PLASTICIZER: Material added to resins to make them softer and more flexible when cured.
PLASTIC LEADED CHIP CARRIER (PLCC): A chip carrier packaged in plastic, usually terminating in compliant leads (originally “J” style) on all four sides.
PLATED-THROUGH HOLE: A hole in which electrical connection is made between printed wiring board layers with conductive patterns by the deposition of metal on the wall of the hole. (see PTH).
PLATING VOID: The area of absence of a specific metal from a specific cross-sectional area: (1) When the plated-through hole is viewed as cross-sectioned through the vertical plane, it is a product of the average thickness of the plated metal times the thickness of the board itself as measured from the outermost surfaces of the base copper on external layers. (2) When the plated-through hole is viewed as cross-sectioned through the horizontal plane (annular method), it is the difference between the area of the hole and the area of the outside diameter of the through-hole plating.
PLOWING: Furrows in the hole wall due to drilling.
POLYMER: A high-molecular-weight compound made up of repeated small chemical units. For practical purposes, a polymer is a plastic. The small chemical unit is called a mer, and when the polymer or mer is cross-linked between different chemical units (e.g., styrene-polyester), the polymer is called a copolymer. A monomer is any single chemical from which the mer or polymer or copolymer is formed.
POLYMERIZE: To unite chemically two or more monomers or polymers of the same kind to form a molecule with higher molecular weight.
POTLIFE: The time during which a liquid resin remains workable as a liquid after catalysts, curing agents, promoter, etc., are added. It is roughly equivalent to gel time.
POWER FACTOR: The cosine of the angle between the applied voltage and the resulting current.
PRECISION: The ability to repeatedly place the hole at any location.
PREPRODUCTION TEST BOARD: A test board (as detailed in IPC-ML-950) the purpose of which is to determine whether, prior to the production of finished boards, the contractor has the capability of producing a multilayer board satisfactorily.
PRESS PLATEN: The flat heated surface for the lamination press used to transmit heat and pressure to lamination fixtures and into the lay-up.
PRESSURE FOOT: The tube like device on the drilling machine that descends to the top surface of the stack, holding it firmly down, before the drill descends through the pressure foot to remove chips and dust formed in drilling.
PRINTED WIRING ASSEMBLY DRAWING: A document that shows the printed wiring base, the separately manufactured components which are to be added to the base, and any other information necessary to describe the joining of the parts to perform a specific function.
PRINTED WIRING LAYOUT: A sketch that depicts the printed wiring substrate, the physical size and location of electronic and mechanical components, and the routing of conductors that interconnect the electronic parts in sufficient detail to allow for the preparation of documentation and artwork.
PRODUCTION MASTER: A 1:1 scale pattern used to produce one or more printed wiring or printed circuit products within the accuracy specified on the master drawing.
PROMOTER: A chemical, itself a feeble catalyst, that greatly increases the activity of a given catalyst.
PTH: Plated-through holes. Also refers to the technology that uses the plated-through hole as its foundation.
QUADPACK: Generic term for surface mount technology packages with leads on all four sides. Commonly used to describe chip carrier-like devices with gull wing leads.
QUALITY CONFORMANCE CIRCUITRY AREA: A test board made as an integral part of the multilayer printed board panel on which electrical and environmental tests may be made for evaluation without destroying the basic board.
RAW MATERIAL PANEL SIZE: A standard panel size related to machine capacities, raw material sheet sizes, final product size, and other factors.
REGISTER MARK: A mark used to establish the relative position of one of more printed wiring patterns, or portions thereof, with respect to desired locations on the opposite side of the board.
REGISTRATION: The relative position of one of more printed wiring patterns, or portions thereof, with respect to desired locations on a printed wiring base or to another pattern on the opposite side of the base.
REPAIR: The correction of a printed wiring defect after the completion of board fabrication to render the board as functionally good as a perfect board.
RESIN: High-molecular-weight organic material with no sharp melting point. For current purposes, the term “resin,” “polymer,” and “plastic” can be used interchangeably.
RESIST: A protective coating (ink, paint, metallic plating, etc) used to shield desired portions of the printed conductive pattern from the action of etchant, solder, or plating.
RESISTIVITY: The ability of a material to resist passage of electric current through its bulk or on a surface.
RIFLING: Spiral groove or ridge in the substrate due to drilling.
RIGID/FLEX: A PWB construction combining flexible circuits and rigid multilayer PWBs, usually either to provide a built-in connection or to make a three-dimensional form that includes components.
ROCKWELL HARDNESS NUMBER: A number derived from the net increase in depth of an impression as the load on a perpetrator is increased from a fixed minimum load to as higher load and then returned to minimum load.
RoHS: Acronym for “Restriction of Hazardous Substances,” The name given to a Directive of the European Union meant to reduce certain materials considered detrimental to the Environment.
ROUGHNESS: Irregular, coarse, uneven hole wall on copper or substrate due to drilling.
SCHEMATIC DIAGRAM: A drawing which shows, by means of graphic symbols, the electrical interconnections and functions of a specific circuit arrangement.
SEM: Scanning electron microscope.
SEQUENTIAL BUILD-UP: A process for making multilayer PWBs in which already finished multilayer’s are laminated together to form a higher-layer-count final board, or in which additional outer layers are added to finished multilayer PWBs.
SHADOWING: Etchback to maximum limit without removal of dielectric material from conductors.
SINGLE-IN-LINE PACKAGE (SIP): Component package system with one line of connectors usually spaced 0.100 inch apart.
SMC: Surface mounted component. Component with terminations designed for mounting flush to printed wiring board.
SMD: Surface mounted device. Any component or hardware element designed to be mounted to a printed wiring board without penetrating the board.
SMEAR: Fused deposit left on copper or substrate from excessive drilling heat.
SMOBC: Solder mask over bare copper. A method of fabricating a printed wiring board which results in the final metallization being copper with no other protective metal; but the non-soldered areas are coated by a solder resist, exposing only the component terminal areas. This eliminates tin-lead under the solder mask.
SMT: Surface mount technology. Defines the entire body of processes and components which create printed wiring assemblies without components with leads that pierce the board. Sn-Au-Cu: An alloy used as a replacement for eutectic tin-lead (Sn-Pb) in “lead-free” solders (often referred to, and pronounced as ”snack”).
SOI: SOIC package with J-leads rather than gull wing leads.
SOIC: Small-outline integrated circuit. A plastic package resembling a small dual-in-line package (DIP) with gull wing leads on two sides for surface mounting.
SOT: Small outline transistor. A package for surface-mounting transistors.
SPINDLE RUNOUT: The measure of the wobble present as the drilling machine spindle rotates 360°.
STORAGE LIFE: The period of time during which a liquid resin or adhesive can be stored and remain suitable for use. Also called shelf life.
STRAIN: The deformation resulting from a stress. It is measured by the ratio of the change to the total value of the dimension in which the change occurred.
STRESS: The force producing or tending to produce deformation in a body. It is measured by the force applied per unit area.
SUBSTRATE: A material on whose surface an adhesive substance is spread for bonding or coating. Also, any material which provides a supporting surface for other materials used to support printed wiring patterns.
SURFACE RESISTIVITY: The resistance of a material between two opposite sides of a unit square of its surface. It may vary widely with the conditions of measurement.
SURFACE SPEED: The linear velocity of a point on the circumference of a drill. Given in units of surface feet per minute-sfm.
Td: Thermal Decomposition Temperature. Glass Decomposition Temperature (physical characteristic/Breakdown Point). Measure of weight loss under temperature (material breaking down as volatile escape). The point where 5 percent of the original mass is lost to decomposition
TERMINAL AREA: A portion of a conductive pattern usually, but not exclusively, used for the connection and/or attachment of components.
TEST COUPON: A sample or test pattern usually made as an integral part of the printed board, on which electrical, environmental, and micro sectioning tests may be made to evaluate board design or process control without destroying the basic board.
TETRA-ETCH: A nonpyrophoric (will not ignite when exposed to moisture) proprietary etchant.
TETROFUNCTIONAL: Describes an epoxy system for laminates that has four cross-linked bonds rather than two and results in a higher glass transition temperature, or Tg.
Tg: Glass transition temperature. The temperature at which laminate mechanical properties change significantly. A higher glass transition temperature delays the onset of rapid thermal expansion and therefore reduces total expansion within a temperature range.
THERMAL CONDUCTIVITY: The ability of a material to conduct heat; the physical constant for the quantity of heat that passes through a unit cube of a material in a unit of time when the difference in temperatures of two faces is 1°C.
THERMOPLASTIC: A classification of resin that can be readily softened and resoftened by repeated heating.
THERMOSETTING: A classification of resin which cures by chemical reaction when tested and, when cured, cannot be resoftened by heating.
THIEF: An auxiliary cathode so placed as to divert to itself some current from portions of the work which would otherwise receive too high a current density.
THIXOTROPIC: Said of materials that are gel-like at rest but fluid when agitated.
THROUGH-HOLE TECHNOLOGY: Traditional printed wiring fabrication where components are mounted in holes that pierce the board.
THROWING POWER: A measure of the degree of uniformity with which metal is deposited on an irregularly shaped cathode. Often refers to the ratio of amount of plated metal on the surface of a copper clad board to the amount plated on a side of a hole through the same board.
TMA: Thermal momechanical analyzer. Specific test procedure used to measure how long a material will resist blistering or delamination at a specific temperature. Time to delamination. More complex resin systems are harder to measure with TMA; DSC and especially DMA are preferred techniques of measuring or accompanied with TMA.
T260 = Time to delamination test at 260C°. Simple way to screen materials for compatibility with lead-free assembly.
T288 = time to delamination test at 288C°. Simple way to screen materials for compatibility with lead-free assembly.
TWIST: A laminate defect in which deviation from planarity results in a twisted arc.
UNDERCUT: The reduction of the cross section of a metal foil conductor caused by the etchant removing metal from under the edge of the resist.
VAPOR PHASE: The solder-reflow process that uses a vaporized solvent as the source for heating the solder beyond its melting point, creating the component-to-board solder joint.
VIA: A metalized connecting hole that provides a conductive path from one layer in a printed wiring board to another. (1) Buried via-connects one inner layer to another inner layer without penetrating the surface. (2) Blind via-connects the surface layer of a printed wiring board to an internal layer without going all the way through the other surface layer.
VOID: A cavity left in the substrate.
VOLUME RESISTIVITY: The electrical resistance between opposite faces of a 1-cm cube of insulating materials commonly expressed in ohm-centimeters. The recommended test is ASTMD 256 51T. Also called the specific insulation.
VULCANIZATION: A chemical reaction in which the physical properties of an elastomer are changed by causing the elastomer to react with sulfur or some other cross-linking agent.
WATER ABSORPTION: The ratio of the weight of water absorbed by a material to the weight of the dry material.
WEAVE EXPOSURE: A condition in which the unbroken woven glass cloth is not uniformly covered by resin.
WEAVE TEXTURE: A surface condition in which the unbroken fibers are completely covered with resin but exhibit the definite weave pattern of the glass cloth.
WETTING: Ability to adhere to a surface immediately upon contact.
WICKING: Migration of copper salts into the glass fibers of the insulating material.
WORKING LIFE: The period of time during which a liquid resin or adhesive, after mixing with catalyst, solvent, or other compounding ingredients, remains usable. (See potlife.)