Acceptable Quality Level:The maximum number of defects per every 100 units that are considered to be satisfactory as a process average.

Acrylic: A synthetic resin made from acrylic acid or a derivative thereof. Acrylics possess the property of transparency, as well as offer flame resistance.

Activated Rosin Flux: A mixture of rosin and small amounts of organic-halide activators or organic-acid activators.

Activators: A substance that enhances the ability of a flux to remove oxides and other contaminants from surfaces being joined.

Active Components: Electronic components such as semiconductors, transistors, diodes, etc., that can operate on an applied electrical signal and change its basic characteristics (e.g., switching, amplification, rectification).

Active Hold-Down: The process of pressing a component lead directly in contact with a bonding pad during soldering to ensure intimate contact between the lead and pad. Intimate contact is important for proper heat transfer through the lead to reflow the solder. This is a characteristic of hot bar soldering, which utilizes a thermode to press the leads against the bonding pads.

Additive Plating: A process in which the conductive, resistive, and insulating materials are successively plated to define traces, pads, and elements.

Adhesion: The state in which two surfaces are held together by means of interfacial forces.

Adhesive: A substance capable of holding materials together by surface attachment.

Adsorption: The adhesion of gases or liquid molecules to the surface of solids or liquids with which they are in contact.

Aerosol: Fluid or gas particles small enough to be airborne.

Aerososl: Fluid or gas particles small enough to be sprayed.

Aging: The change in the properties of a material over time and under varying conditions of humidity, temperature, pressure, etc.

Alignment Holes (or Tooling Holes): Holes specifically designed in TAB tape for registration of a TAB frame. These holes can be located virtually anywhere on the tape site, however, locations are standardized in many cases.

Alloy: A mixture of two or more metals combined to achieve properties, such as a lower melting point or greater strength, that the individual metals do not possess.

Analog Circuit: An electrical circuit that provides a continuous relationship between its input and output.

Angle of attack: The angle between the squeegee face and the plane of the stencil.

Anisotropic Conductive Adhesive: Conductive adhesives that conduct electricity in one direction only. Also referred to as "Z-axis conductive adhesives." When using this type of adhesive, high Z-axis forces are required during bonding. Components attached using this material use the pick, place, and attach process.

Anisotropic: A material that exhibits different properties when tested along axes in different directions.

AOI: To inspect a pattern or object using a camera in an automated system.

APQP: Advanced Product Quality Planning is a structured method of defining and establishing the steps necessary to assure that a product satisfies the customer. The goal of a product quality planning is to facilitate communication with everyone involved to assure that all required steps are completed on time.

Aqueous Cleaning: A cleaning technique that uses water as the primary cleaning fluid.

Area Array TAB: A mounting configuration for a TAB frame to an IC where the inner leads are connected to bumps in an array pattern on the surface of the IC instead of on the perimeter, which is the case for typical TAB components.

Array: A group of elements, such as solder bumps, or circuits arranged in rows and columns on a substrate.

ASIC: A custom made circuit used for a specific application.

Assembly: A group of components physically joined to a PCB or ceramic board.

ATE: Equipment that automatically analyzes functional or static parameters to evaluate performance.

Automated Test Equipment: (see ATE)

Automatic optical inspection: (see AOI)

Azeotrope: A blend of two or more polar and nonpolar solvents that act as a single solvent and can be used to remove both polar and nonpolar contaminants.

Azeotropic Mixture: A liquid mixture of two or more substances that behaves as a single substance.

B-Stage PCB: Refer to "prepreg."

Ball Grid Array: (See BGA)

Bare Board: An unpopulated PCB.

Bed-of-Nails Fixture: A test fixture consisting of a frame and holder containing a field of spring-loaded pins that make electrical contact with a planar test object.

Bend Radius: The radius at the inside of the bends at both the lead shoulder leading to the leg and the base of the leg leading to the foot.

BGA: A leadless surface-mountable package in which solder ball interconnects cover the bottom surface of the package in a checkboard fashion. BGAs are reflow soldered to PCBs using a mass reflow process.

Board: An organic printed circuit card or board on which smaller components, cards, or modules can be mounted.

Body: The insulating part of an interconnect.

Bond lift-off : A failure by separation of a bonded (or soldered) lead from the pad surface (substrate).

Bond Strength : The force per unit area required to separate two adjacent layers of a package. The force is applied perpendicular to the surface of the package.

Bonding Alloy: A term sometimes substituted for solder. The "bonding alloy" can be application specific; the most common to fine pitch bonding is eutectic Sn/Pb solder.

Bonding Pads: Copper traces, or pads, on a substrate to which leads are bonded. Dimensions and thermal path from the bonding pads must be properly designed to achieve uniform solder reflow.

Bonding: The joining of two materials. For instance, the attachment of a component to a substrate.

Boundary Scan: An approach to the testing of printed circuit board assemblies that can be used to diagnose individual circuit failures by embedding the test circuits into the board and in the most failure-prone integrated circuits.

Breakaway panels: PCBs held together with breakaway tabs to make handling, placement and soldering easier and more efficient. Boards are snapped apart at the end of processing.

Bridge: Solder that effectively joins two conductors that should not be electrically connected, causing a short.

Built-in Lead Stress: The force within leads of a molded carrier ring or TAB component that result in lead skew or splay after the excising process. Possible causes include the dam bar removal process, the stamping process used to produce lead frames, or stress induced during prior thermal or mechanical processing of the components.

Built-In Self Test: An electrical testing technique in which hardware is added to the chip to allow the integrated circuit to test itself with minimal use of test equipment.

Bump: A small mound formed on the device or the substrate pads that can be used as a contact for face-down bonding. This is a method of providing connections to the terminal areas of a device.

Burn-In: The process in which a device is electrically stressed by subjecting it to an elevated temperature and voltage for an adequate period of time to cause the failure of a marginal device.

Butt Joint: A solder joint where the end of the lead sits on the solder pad.

C-4 (Controlled Collapse Chip Connection): A solder joint connecting a substrate directly to an IC in a flip chip configuration. In this packaging scheme, a solder ball is formed on the IC, the IC is placed active circuitry down onto a substrate, and the solder is reflowed. As the solder melts, the solder balls collapse into a shape controlled by the surface tension of the liquid solder while supporting the weight of the IC.

C-5 (Controlled Collapse Chip Carrier Connection): The same technology as C-4 except the IC is mounted in an intermediate carrier (ceramic or FR-4) using conventional technology, and the chip carrier, having the solder balls, is mounted directly to the substrate and reflowed.

C-Stage: Refer to "laminate."

CAD/CAM: Computer-aided design is the use of special software tools to formulate printed circuit patterns. Computer-aided manufacturing translates such designs into actual products. These systems include mass memory for data processing and storage, inputs for design creation and output devices for converting stored information into drawings and reports.

Capillary Action: The effect of surface tension that draws a liquid into a small opening. So a combination of natural causes that forces molten solder to flow against gravity between closely spaced solid surfaces.

Card: A printed circuit board of smaller dimensions is commonly referred to as a card. A card is generally one level lower than the printed circuit board in the hierarchy of packaging. A card is also referred to as a daughter board.

Ceramic Ball Grid Array (CBGA): A ball grid array package with a ceramic substrate.

Ceramic Column Grid Array (CCGA): The same as CBGA except the solder balls are replaced by solder columns. The advantage of columns is that the inherent flexibility of the columns help compensate for CTE mismatch between the ceramic component and the FR-4 board. Columns are required rather than solder balls for components greater than 25mm square.

Ceramic: An inorganic, nonmetallic material. Examples include alumina or glass-ceramic. Ceramics are often used in forming ceramic substrates for the packaging of semiconductor chips.

CFC: A chlorinated fluorocarbon that can cause ozone layer depletion. The use of CFCs is restricted by the Environmental Protection Agency. CFCs are primarily used in air conditioning and refrigeration, foam insulators, and cleaning solvents.

Chip Carrier: An integrated circuit package that is usually square and may possess a cavity for a chip in the center and whose connections are typically on all four sides.

Chip-on-Board : (see COB)

Chip: The individual circuit or component of a silicon wafer. The leadless form of an electronic component part, either passive or active, discrete or integrated.

Circuit: The interconnections of electrical elements and devices that perform a desired electrical function.

Circuit tester: (see ICT)

Clamshell Fixture: An in-circuit test fixture designed to probe both sides of a PCB.

Cleaning: An operation involving the removal of flux residues and other contaminants from the surface of a PCB assembly.

Cluster Testing: A variation of the in-circuit testing procedure in which a cluster of components are tested as a functional unit.

Coating: A thin layer of material, conductive or dielectric, applied over components or a base material.

COB: A configuration in which a face-up bonded chip is directly attached to a printed circuit board or substrate and exclusively interconnected to the substrate conventionally, i.e., by flying wires.

Coefficient of Thermal Expansion (CTE): The ratio of change in dimensions to original dimensions per degree rise in temperature, expressed in ppm/ºC.

Cofiring: A process for forming multilayer ceramic substrates in which thick- film conductors and dielectrics are simultaneously processed by a firing cycle.

Cold solder joint: A connection reflecting poor wetting action and characterized by a gray, porous appearance owing to insufficient heat or inadequate cleaning.

Comb Pattern: A set of comb-like arrays of uniformly spaced conductors.

Component: An individual functional element in a physically independent body (e.g., resistor, capacitor, or transistor).

Component densityt: The number of parts on a PCB divided by board area.

Component Lead: A wire or formed conductor that extends from a component and serves as a mechanical and/or electrical connection. Leads can readily be formed to a desired configuration.

Conduction: The thermal transmission of heat energy from a hotter region to a cooler region in the presence of a conducting medium.

Conductive Adhesive: Refer to "isotropic/anisotropic conductive adhesives."

Conductor, Electrical: A class of materials-ususally metals-that easily conducts electricity. Examples include silver, copper, gold, and super-conducting ceramics.

Conductive Epoxy: A polymer material made to pass electrical current by the addition of metal particles, usually silver.

Conductor, Thermal : A class of materials-ususally metals-that easily conduct heat. Examples include copper, aluminum, and beryllia.

Conformal Coating: A thin nonconducting coating that is either plastic or inorganic and is applied to a circuit for environmental and mechanical protection.

Contact Angle: The angle between bonding material and a bonding pad. Also called the wetting angle.

Contact Printing: A type of printing where there is no gap between the stencil and the substrate.

Contact Resistance: The maximum resistance allowed between a pin and the socket contacts of a connector when assembled and in use.

Contact Time: Refer to "Dwell time."

Contaminant: An undesirable material that can adversely influence the properties of a material or the quality of a product. A contaminant can be liquid or solid.

Continuous Tape: A TAB tape handling scheme that uses a continuous reel of polyimide tape to mount and carry TAB components through the assembly process. Typically, the tape width conforms to industry standards, with 35mm, 48mm, and 70mm widths being the most common.

Convection: The transfer of heat by movement of hot air. (Often used in conjunction with infrared radiation to reduce the effect of IR shadowing. )

Coplanarity: The maximum distance between the lowest pin and the highest pin when a package rests on a perfectly flat surface.

Copper foil: A cathode-quality electrolytic material deposited as a thin, continuous sheet on substrates as a conductor for PCBs. It readily bonds to insulators, accepts the printed resists and etches out to form the circuit pattern.

Copper mirror test: A flux corrosivity test using a vacuum-deposited film on a glass plate.

Corrosion: A chemical action that causes the gradual deterioration of the surface of a metal by oxidation or chemical reaction.

Corrosive Flux: A flux that contain levels of activators like halides, amines, or organic acids that can cause the corrosion of copper.

CTE Mismatch: The difference in the coefficients of thermal expansions of two materials or components joined together, which produces strains and stresses at joining interfaces or in attachment surfaces.

Curing Cycle: The time-temperature profile needed to cure a thermosetting material like a bonding adhesive.

Curing Time: The time needed to properly cure a thermosetting plastic material.

Curing: A change in the physical properties of a material via chemical reaction or by reaction to temperature-time profile.

Cycle rate: A component placement term measuring machine speed from pickup to board location and return. Also called the test rate.