Glossary of Terms

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A

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.

Active Trim: Trimming of a circuit element (usually resistors) in a circuit that is electrically activated and operating to obtain a specified functional output for the circuit (see Functional Trimming)

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 for registration of a substrate. These holes can be located virtually anywhere on the substrate, 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.

Alumina: Aluminum oxide (Al2O3). Alumina substrates are made of formulations that are primarily (96 to 99%) alumina

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 screen or 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.

Annular Ring: That portion of conductive material completely surrounding a hole.

AOI: (Automatic Optical Inspection) To inspect a pattern or object using a camera in an automated system.

AQL: Abbreviation for "Acceptable Quality Level". A method of random sampling rather than 100 percent inspection.

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

Aqueous Flux: An organic-chemical soldering flux that is soluble in water.

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.

Artwork: The accurately scaled configurations or patterns produced to enable the product to be made; photographic films which are created to produce working thick film screens and thin film masks.

As-Fired: Values of thick-film resistors or smoothness of ceramic substrates as they come out of the firing furnace and prior to any trimming and polishing.

Aspect Ratio: The ratio between the length of a film resistor and its width; equal to the number of squares of the resistor.

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

Assembly Drawing: A drawing or depiction showing all the components and interconnections mounted or soldered to the film circuit in their proper position.

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

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.

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B

Bake Out: Subjecting an unsealed hybrid circuit package to an elevated temperature to "bake out" moisture and unwanted gases prior to final sealing.

Ball Bond: An attachment formed when a ball shaped end interconnecting wire is deformed by thermo-compression against a metallized pad. The bond is also designated a "Nailhead Bond" from the appearance of the flattened ball.

Ball Grid Array [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.

Bare Board: An unassembled (unpopulated) printed board.

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.

Bias Cut: Material cut at 45 degrees from the normal weave pattern.

Binder The organic or inorganic material which encapsulates and holds together the base in reinforced or otherwise heterogeneous composites.

Blind Via: A via hole extending only to one surface of a printed circuit board.

Blister: A localized swelling and separation between any of the layers of a laminated base material, or between base material and conductive foil. It is a form of delamination.

Blow Hole: A void caused by outgassing. (Outgassing is a gaseous emission from a printed circuit assembly when exposed to a reduced pressure or heat or both.

Bond: An interconnection that performs a permanent electrical and/or mechanical function.

Bond Strength: In wire bonding, the pull force at rupture of the bond interface measured in the unit gram-force.

Bonding Di: Attaching the semiconductor chip to the substrate, either with an epoxy, eutectic or solder alloy.

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

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.

Bow: The deviation from flatness of a board characterized by a roughly cylindrical or spherical curvature such that if the board is rectangular, its four corners are in the same plane.

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

British Thermal Unit (B.T.U.): The quantity of heat required to raise the temperature of one pound of water 1°F from 58.5°F to 59.5°F (its point of maximum density).

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.

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C

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.

Camber: A term that describes the amount of overall warpage present in a substrate.

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.

Celsius: also referred to as Centigrade, is equal to the difference between the temperature in Fahrenheit less 32 and the quantity divisible by 1.8. formula: °C = (°F-32) ÷ 1.8

Centrifuge: Testing the integrity of bonds in a hybrid circuit by spinning the circuit at a high rate of speed thereby imparting a high G loading in the interconnecting wire bonds and bonded elements.

Ceramic: Inorganic nonmetallic material such as alumina, beryllia, steatite, or for sterite, whose final characteristics are produced by subjection to high temperatures, often used in microelectronics as parts of components, substrate, or package.

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.

Chamfered Corner:  Used for rapid orientation in fixture during processing.

Chip: The uncased and normally leadless form of an electronic component part, either passive or active, discrete or integrated.

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 : [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.

Chip and Wire: A hybrid technology employing face-up bonded chip devices exclusively, interconnected to the substrate conventionally by flying wires.

Circuit: The interconnection of a number of electrical elements and /or devices, performing a desired electrical function.

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

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

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

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

Co-Firing: Processing more than one type of the thick-film paste through the firing cycle at the same time - usually refers to conductors and resistors

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 density: 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.

Conductivity: The ability of a material to conduct electricity; the reciprocal of resistivity.

Conductor Spacing:  The distance between adjacent conductor film edges.

Conductor Width: The width of individual conductors in a conductive film pattern.

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

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

Conductive Epoxy: An epoxy material (polymer resin) that has been made conductive by the addition of a metal powder, usually gold or silver.

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

Conformal Coating: A thin non-conducting 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 Belt Furnace: A firing furnace that has a continuous belt, carrying the unfired substrates through the firing cycle.

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.

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.

Crazing: Minute lines appearing in or near the surface of materials such as plastics, usually resulting as a response to environment. Crazing cannot be felt by running a fingernail across it (if the fingernail catches , it is a crack).

Crossover: Transverse crossing of metallization paths without mutual electrical contact and achieved by the deposition of an insulating layer between the conducting paths at the area of crossing.

Crosstalk: Signals from one line leaking into another nearby conductor because of capacitance or inductive coupling or both (e.g. owing to capacitance of a thick-film crossover).

CTE: (Coefficient of Thermal Expansion) A characteristic thermomechanical property of a material or a composite. It is the tendency of a material to expand as it is heated. In laminate, in-plane (x and y direction) and out-of-plane (z-direction).

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.

Cut and Strip: An essentially obsolete method of producing artwork using a two-ply laminated plastic sheet, by cutting and stripping off the unwanted portion of the opaque layer from the translucent layer, leaving the designed art work configuration.

Cure: To change the physical, chemical, or electrical properties of a material by chemical reaction, by the action of heat and catalysts alone or in combination, with or without pressure. Specifically to convert a low molecular weight polymer or resin to and insoluble, infusible state.

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.

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D

DCA: Direct Chip Attach. A chip-to-substrate connection intended to reduce the first level of packaging. Here, the silicon die is inverted and mounted directly to the Substrate. Also referred to as chip-on-board technology.

Defect: Any nonconformance to specified requirements by a unit or product.

Definition: The sharpness of a screen-printed pattern - the exactness with which a pattern is printed.

Deionized Water: Water that has been treated to remove ionized material.

Delamination: A separation between plies within the base material, or between the base material and the conductive foil, or both.

Dendritic Growth: The metallic growth between pads in the presence of moisture and an electrical bias.

Density: The weight of a material in relationship to its volume.

Device: An individual electrical circuit element that can't be further reduced without destroying its intended function.

Dewetting: A situation where a lead or pad was at one point in the soldering process wetted by the solder, but due to extended time or temperature, the presence of intermetallics, volatiles or other causes, has become withdrawn from the wetted surface.

Die Bonder: The placement machine for chips in a chip-on-board process line.

Die Bonding: The attachment of an integrated circuit chip to a substrate.

Die Sorter: Equipment that picks die from a wafer and presents them for their next process step. When used in reference to bare die placement machines, the die are presented for pick by the machine's placement nozzles.

Die: Integrated circuit chip as diced or cut from the finished wafer.

Dielectric: Materials that do not conduct electricity and that are used for making capacitors, for insulating conductors (as in crossover and multi-layered circuits), and for encapsulating circuits.

Dielectric Constant: The term used to describe a material's ability to store charge when used as a capacitor dielectric. It is the ratio of the charge that would be stored with free space as the dielectric to that stored with the material in question as the dielectric.

Dielectric Layer: A layer of dielectric material between two conductor plates.

Diffusion: A material transport phenomena that occurs in solids, and is caused by the continual physical motion of atoms from one position to another. This results in the flow of material from regions of high concentraion to regions of low concentration.

DIP Socket: A connector for a Dual In-Line Package, or one that has its leads in two parallel rows.

Double-Sided Assembly: A fully assembled PCB with components on both sides of the substrate.

Downtime: The period in which equipment is not producing product owing to maintenance or failure.

Drilled Hole: Used to make front-to-back connections; (vias), mounting holes or access ports, (feed-throughs).

Dross: Any oxide or other contamination formed on the surface of molten solder.

Dual In-Line Package (DIP): A package with two rows of leads extending at right angles from the base with standard spacing between the leads and row. This package is intended for through hole mounting.

Durometer: The measure of rubber or plastic hardness, as with the squeegee blade.

Dynamic Flex: A flex circuit in constant motion, for example, in a printer head.

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E

Elastomeric: A material that at room temperature can be stretched repeatedly to at least twice its original length, and upon release of the stress, will return with force to its approximate original length. A rubber band is an example.

Electrode: A conductor through which a current enters or leaves an electrolytic cell, vacuum tube, or any nonmetallic conductor.

Electroless Plating: Deposition of metal (without any external electric current) by an exchange reaction between metal complexes in the solution and the metal being coated.

Electroplating: A method of electrically depositing metals of very precise compositions and thicknesses onto a base metal.

Electromigration: The electrolytic transfer of metal from one conductor to another conductor separated from the first conductor by a dielectric medium.

Electronic Packaging: The technology of interconnecting semiconductor and other electronic devices to provide an electronic function.

Electroplating: Deposition of metal onto a cathodic surface by passing DC current into an electrolytic solution.

Elongation: The fractional increase in length of a material stressed in tension.

Emissivity: The ratio of the radiant energy emitted by a source to the radiant energy of a perfect radiating surface (black box) having an equivalent surface area with all other relevant conditions being the same.

Emulsion: A stable mixture of two or more immiscible liquids held in a suspension by small percentages of emulsifiers.

Encapsulant: The material used to cover devices to provide mechanical protection and to ensure reliability, typically an epoxy.

Encapsulate: Sealing up or covering an element of circuit for mechanical and environmental protection.

Encapsulation: The sealing or covering of an element or circuit for the purpose of mechanical and environmental protection.

Environmental Test: A test or series of tests used to determine the sum of external influences affecting the structural, mechanical, and functional integrity of any given package or assembly

Epoxy Resin: A material that forms straight chain thermoplastic and thermosetting resins. Expoxy resins have excellent mechanical properties and good dimensional stability.

Epoxy: A thermosetting polymer containing the oxirane group.

Eutectic: The minimum melting point of a combination of two or more materials. The eutectic temperature of an alloy is always lower than the melting point of any of its individual constituents. The eutectic temperature is the particular temperature at which the eutectic occurs. Eutectic alloys, when heated, transform directly from a solid to a liquid and do not show any pasty regions. For example, eutectic solder paste has a composition of 63% tin (Sn) and 37% lead (Pb), and has a eutectic temperature of 183ºC.

Excising: Cutting component leads free from the remainder of the package to prepare the component for forming or placement.

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F

Failure: The temporary or permanent functional impairment of a component or device caused by physical, mechanical, chemical, or electrical damage.

Failure Rate: The rate at which devices form a given population can be expected (or were found) to fail as a function of time (e.g. percent per 1000 hr of operation).

Fahrenheit:  Equals 1.8 multiplied to the sum of the temperature in Celsius and 32. formula: - °F = 1.8 x (°C + 32)

Fiducial: A specific mark incorporated in the circuit artwork and used by machine vision to identify artwork orientation and location.

Filler Materials: Ceramic or metallic particles used to modify the properties of polymers.

Fillet: A smooth, concave junction where two surfaces meet. The quality of a solder fillet determines the strength of the joint.

Film: Single or multiple layers or coatings of paste material used to form various elements (resistors, capacitors, inductors) or interconnections and crossovers (conductors, insulators). Thick films are deposited by screen printing.

Final Seal:  The manufacturing operation that completes the enclosure of the hybrid microcircuit so that further internal processing cannot be performed with out de-lidding or disassembling the package.

Fine Leak: A leak in a sealed package less than 10-5 cm3/sec at one atmosphere of differential air pressure

Fine Pitch: Surface mount components with a lead pitch of at least 50 mils. Fine pitch is more commonly used to refer to components with a lead pitch of 25 mils or less. These packages usually require vision assistance for accurate placement.

Fire: The term used to describe the act of heating a thick-film circuit so that the resistors, conductors, capacitors, and other integrated elements will be transformed into their final form.

Fixture: A device that interfaces the PCB to the process machine center(s).

Flat Pack: An integrated circuit package with leads on two or four sides. The leads on these packages are either gull wing or flat, and have standard spacing. Packages with a lead pitch below 50 mils are referred to as fine pitch packages.

Flex Circuits: Flexible printed circuit boards made using thin polyimide or polyester film with copper circuitry on one or both sides of the flex. Flex circuits can be single or multilayer.

Flip Chip: Any packaging scheme in which the active circuitry of an IC is placed facing the surface of the substrate. So A leadless structure which is designed to electrically and mechanically interconnect to the circuit by means of an appropriate number of bumps located on its face which are covered with a conductive bonding agent. Examples are flip TAB and C-4.

Flip Chip interconnection:  In this process, the bumped device is mounted to the substrate active side down. The technique is called "flip chip" because the active circuitry faces down instead of up, as in the case of wire bonded devices.

Flip TAB: A mounting configuration for a TAB component where the active circuitry of the IC is placed facing the surface of the substrate.

Flood bar: A device on a screen or stencil-printing system that drags paste back to the starting point after the squeegee has made a printing stroke.

Fluorocarbon: The liquid vaporized in Vapor Phase reflow soldering.

Flux Activation Temperature: The temperature at which flux is active enough to remove oxides from the metals being joined.

Flux Activity: The efficiency of a flux to promote the wetting of a surface with molten solder.

Flux Characterization: Tests performed to determine the properties of fluxes and flux residues.

Flux Residue: A flux-related contaminant present on or near the surface of a solder connection.

Flux Solder Connection: A solder joint with entrapped flux, causing high electrical resistance.

Flux: A chemically- or physically-active formulation capable of cleaning oxides and enabling wetting of metals with solder.

Foot Angle: The angle of the lead foot after lead forming with respect to the plane defined by the bottom of the component.

Foot Length: The part of the component lead that comes in contact with the bonding pad on the substrate.

Footprint: The pattern on the printed circuit board to which the leads on a surface mount component are mated. Also called a land or a pad.

Functional Test: The electrical testing of an entire assembly that simulates the intended function of the product.

Functional Trimming: Trimming of a circuit element (usually resistors) on an operating circuit to set a voltage or current of the output.

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G

Gang Bonding: A process in which multiple mechanical or electrical bonds are made by means of a single stroke of a bonding tool.

GelPak: A matrix tray style feeder without pockets, that consists of a tacky gel over a mesh. The components are placed in a regular array on the tray and are held in place by the tacky gel. When picking components, vacuum is applied through the bottom of the tray, pulling the gel through the mesh and releasing the die.

Glass Fabric: Glass yarns woven in a specific pattern.

Glass Transition Temperature: The temperature above which a polymer loses its properties of glass and behaves as an elastomer. Glass transition temperature is characterized by a decrease in elastic modulus and an increase in CTE.

Golden boy: A component or assembly tested and known to function to a specification, then used to test other units via comparison.

Green: A term used in ceramic technology meaning unfired (for example, a "green" substrate is one that has been formed, but has not been fired).

Green Strength: The strength of a substance, joint, or assembly before it has been cured.

Gross Leak: A leak in a sealed package greater than 10-5 cm3/sec at one atmosphere of differential air pressure.

Ground Plane:   An electrically-conductive plane in a multilayer circuit that connects a number of circuit elements to grounding electrodes.

Gull Wing Lead: A lead configuration, usually found on small outline packages, where the leads are bent. The end view of these packages resembles a gull in flight.

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H

Halo: A bright or dark ring around a drop of molten solder on a flat surface.

Hard water: Water containing calcium carbonate and other ions that may collect on cleaning equipment interiors and cause clogging.

Hardener: A chemical added to a resin to advance curing, i.e., a curing agent.

Header: The base of a hybrid circuit package that holds the leads.

Heat Sink: The supporting member to which electronic components or their substrate or their package bottom are attached. This is usually a heat conductive metal with the ability to rapidly transmit heat from the generating source (component).

Heat Treating:   A process that uses precise heating and cooling of metals after stamping and forming in order to optimize internal stresses and spring properties.

Hermetic: The sealing of an object so it is airtight.

Hot Bar Soldering: A process in which a heated bar simultaneously solders all the leads of a device to the pads on a Substrate.

Hot Gas Reflow: A solder reflow process that uses a heated gas, including air, as the mode of heat transfer.

Hot Spot: A small area on a circuit that is unable to dissipate the generated heat and therefore operates at an elevated temperature above the surrounding area.

Hybrid Circuit: A microcircuit consisting of elements which are a combination of the film circuit type and the semiconductor circuit type or a combination of one or both of these types and may include discrete add-on components.

Hybrid Microelectronics: The entire body of electronic art which is connected with or applied to the realization of electronic systems using hybrid circuit technology.

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I

Inert Atmosphere: A gaseous atmosphere that is not conducive to chemical reactions, such as helium or nitrogen.

Infant Mortality: (Early Failures) The time during which circuits are failing at a decreasing rate (during the first few hundred hours of operation).

InfraRed (or IR) Reflow: A technique in which long wavelength light serves as the heat source to reflow solder and form solder joints.

Ink: Synonymous with "composition" and "paste" when relating to screenable thick-film materials, usually consisting of glass frit, metals, metal oxide, and solvents.

Innovation: Innovation is the whole process from: invention, development, pilot production, marketing, production. Invention is just invention (.Innovation = creative idea + implementation.)

IR Shadowing: When connector bodies or other components prevent the infrared energy from directly striking some solder joints, causing non-uniform heating.

Inorganic Flux: An aqueous flux solution of inorganic acids and halides.

Insulation Resistance: The resistance to current flow when a potential is applied (IR is typically measured in megohms).

Insulators: A class of materials that do not conduct electricity and are characterized by high resistivity.

Integrated Circuit: A microcircuit that consists of interconnected elements inseparably associated and formed in-situ on or within a single substrate, usually silicon, to perform an electronic circuit function.

Interconnect: The conductive path required to achieve connection from one circuit element to another.

Interconnection: The conductive path required to achieve a connection from a circuit element to the remainder of the circuit.

Intermetallic: Chemical compounds formed between the metals present in the solder, base metal and protective platings. Intermetallic formation is necessary for good solder joints, but excessive intermetallics can cause brittleness.

Isotropic Conductive Adhesive: Isotropic adhesives conduct electricity in all directions. This means the adhesive can be dispensed only on those areas (pads) where a circuit path is required (i.e., where bumps will attach).

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J

J-Lead: A lead configuration usually used on plastic chip carrier packages. J-leads are bent underneath the body of the package, with a side view resembling the shape of the letter "J."

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K

Kelvin: The absolute temperature scale (metric). formula: - K = °C + 273

Kerf: The slit or channel cut in a resistor during trimming by laser beam or abrasive jet.

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L

L-Cut: A trim notch in a film resistor that is created by the cut starting perpendicular to the resistor length and turning 90 degrees to complete the trim parallel to the resistor axis thereby creating an L-shaped cut

Laminar Flow: A constant and directional flow of filtered air across a clean workbench. The flow is usually parallel to the surface of the bench.

Laminate: A stack of prepregs with copper foils on either surface after lamination during PCB fabrication.

Lamination: A heat and pressure cycle used to consolidate a stack of prepregs into a solid block. The term also refers to the consolidation of a stack of laminates (with circuitry) to form a PCB. Lamination is referred to as the C-stage in PCB fabrication.

Land Pattern: The complete configuration of the lands to which a surface mount component is attached. Also called a footprint or a pad.

Land: Widened conductor areas on the major substrate used as attachment points for wire bonds or the bonding of chip devices.

Laser: An acronym for "Light Amplification by Stimulated Emission of Radiation."

Laser Marking: Used for part or surface identification.

Laser Soldering: A method of soldering in which the heat required to reflow a solder interconnection is provided by a laser (YAG or CO2). In this process, the solder joints are heated sequentially and cooled rapidly.

Laser Trim: The adjustment (upward) of a film resistor value by applying intense localized heat from a focused laser source to vaporize material.

Layout: The scale depiction (drawing) in two dimensions of all conductors, resistors and other circuit elements to be fabricated as a film substrate.

Leaching: The movement of metal atoms from the lead base metal into liquid solder. This is prevented by nickel plating. May also refer to alloying of a gold protective plating into the solder.

Lead Configuration: The conductors extending from a device, which function as both mechanical and electrical connection points.

Lead Coplanarity: The position of all of the component leads with respect to one another using a reference plane defined by the three lowest leads of a component.

Lead Forming: After excising, forming the lead into a specific shape or profile required for placement and bonding. The typical lead form profile is a gull-wing shape.

Lead Frame: A sheet metal framework etched to form an array of metal traces (leads). An IC is attached to the lead frame at the innermost portion of the leads, and the outermost portion of the leads is attached to the next level of the assembly. However, lead frames are the basis for molded carrier ring (MCR) and plastic quad flatpack (PQFP) components, while TAB frames are the basis for TAB components.

Lead Pitch: The sum of the lead width and lead spacing. Typically stated as the distance between the center of one lead to the center of an adjacent lead.

Lead Plating: The metal coating on a component lead. Common lead plating materials are pure tin (Sn), pure gold (Au), and eutectic tin/lead solder (63% Sn/37% Pb).

Lead Spacing: The distance between adjacent leads in a defined area of a component.

Lead Thickness: In reference to component leads, it is the sum of the thickness of the base metal, plating, and total fabrication tolerances. Lead thickness is a critical element in determining the dimensions and proper clearances in excise and form tooling.

Lead Width: The width of the lead in a defined area of a component.

Lead: A wire that connects two points in a circuit; it is usually self-supporting.

Leaded Device: Electronic devices that have electrical leads extending from the body of the package.

Leadless Device: Electronic devices which do not have electrical leads extending from the body of the package. These packages could have solder bumps or lands located on the package.

Leakage Current: A small amount of current that flows through or across an insulator between two electrodes.

Leg Angle: The angle of the vertical portion of a lead with respect to a plane perpendicular to the plane defined by the bottom of the component.

Leg Length: The part of the component lead between the two bend radii. The leg length is directly related to the overall lead form height.

LCC: Leadless Chip Carrier.

Life Drift: The change in either absolute level or slope of a circuit element under load. Rated as a percentage change from the original value per 1000 hours of life.

Life Test: Test of a component or circuit under load over the rated life of the device.

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M

Machined Alignment Flats:  Used for precise location with 3-pin fixture. Flat edges provide repeatable positioning. Flats are 2-3 mils deep on parts lasered from larger blanks. They are 15 +/- 10 mils deep when lasered in as-fired edges.

Mask:   The photographic positive (or negative) that serves as the master for making thick-film screens.

Melting Range: The difference between the solidus and liquidus temperature.

Mesh Porosity: The ratio of the amount of open area in a mesh versus the amount of closed area in a mesh.

Mesh Size: The number of openings per inch in a screen. A 325 mesh screen has 325 openings per linear inch, or 105,625 openings per square inch.

Metal Composition: The composition of metals in an alloy that go into solder paste.

Metal Content: The percentage weight of the solder alloy powder in solder paste.

Metallization: A film pattern (single or multi-layer) of conductive material deposited on a substrate to interconnect electronic components, or the metal film on the bonding area of a substrate which becomes a part of the bond and performs both an electrical and a mechanical function.

Metal to Glass Seal: (or glass-to-metal seal) An insulating seal made between a package lead and the metal package by forming a glass bond to oxide layers on both metal parts. in this seal, the glass has a coefficient of expansion that closely matches the metal parts.

Microcircuit: A small circuit (hybrid or monolithic) having a relatively high equivalent circuit element density, which is considered as a single part on (hybrid) or with (monolithic) a single substrate to perform an electronic circuit function. (This excludes print wiring boards, circuit card assemblies, and modules composed exclusively of discrete electronic parts).

Microelectronics: The area of electronic technology associated with or applied to the realization of electronic systems from extremely small electronic parts of elements.

Micron: One millionth of a meter, and another term for micrometer. An easy conversion scheme is to remember that 25.4 microns=0.0254mm=0.001"=1 mil=1,000 microinches. With this formula memorized, it is simple to translate between inch and metric references.

Microstructure of Material: Atomic structure of a material. In bonding applications, refers to the effect of atomic structure on material behavior during various steps in the excise, form, and bonding processes.

Migration:   An undesirable phenomenon whereby metal ions, notably silver, are transmitted through another metal, or across an insulated surface, in presence of moisture and an electrical potential.

Misalignment: Misregistration of the centerline of the component lead with respect to the centerline of the bonding pad on the substrate.

Misregistration: The lack of adequate dimensional conformity between two or more patterns or features. Examples include misregistration of a board with respect to a stencil or the misaligment between layers of a printed circuit board.

Multichip Module: A module capable of supporting several ICs in a single package. Typically, multichip modules are based on ceramic, contain high performance ICs with high pin count, and use some form of advanced interconnect technology such as TAB.. The parameters used to define a multichip module are vague, but one basic criterion is a package that is no less that 20% silicon, has no fewer that 100 I/O on a substrate, and has no fewer that four layers.

Multilayer Board: A substrate that uses more than two layers for conductor routing. Plated via holes are used to connect the internal layers to the outer layers.

Multilayer Ceramic: A stack of alternating metallic and ceramic layers with vias interconnecting them.

Multilayer Ceramic Capacitor: A Miniature ceramic capacitor manufactured by paralleling several thin layers of ceramic. The assembly is fired after the individual layers have been electroded and assembled.

Multilayer Substrate: Substrates that have buried conductors so that complex circuitry can be handled. Assembled using processes similar to those used in multi-layer ceramic capacitors. Cofired multilayer ceramic substrates are also referred to as multilayer substrates.

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N

Neutralizer: An alkaline chemical added to water to improve its ability to dissolve organic acid flux residues.

Nitto tape: Tape that sliced silicon wafers are placed on prior to dicing.

Nominal Resistance Value: The specified resistance value of the resistor at its rated load.

Nonactivated: A natural or synthetic resin flux without activators.

Nonconductive Epoxy : An epoxy material (polymer resin) either without a filler or with a ceramic powder filler added for increasing thermal conductivity and improving thixotropic properties. Nonconductive epoxy adhesives are used in chip to substrate bonds where electrical conductivity to the bottom of the chip is unnecessary or in substrate-to-package bonding

Nonpolar Solvent: A solvent that is not electrically conductive and will dissolve nonpolar compounds such as hydrocarbons and resins.

Nonpolar: A condition in which a substance does not ionize in water.

Nonwetting: A condition in which molten solder has contacted a surface, but the solder has not adhered to all of the surface, and a portion of the base metal may be exposed. Nonwetting occurs when there is a barrier (intermetallic or oxide) between the two joining surfaces.

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O

Off-Contact: A stencil printing method in which the printer is setup so there is a space between the stencil and the substrate.

Ohms/Square: The unit of sheet resistance, or more properly, of sheet resistivity.

Open: A complete break in a metal conductor path or a condition in which solder fails to bridge the gap between lead termination and the pad, resulting in a loss of electrical continuity.

Organic PCB: A printed circuit board made from organic material (epoxy, polyimide, etc.).

Origin (0,0) :  The point of reference for all internal features. Normally a corner of the part or the alignment flat intersection when present.

Outer Lead Bonding: The process of joining the leads of a component to the next level of the assembly immediately following placement. Commonly referred to as OLB. The bonding method can be laser, hot gas, or hot bar.

Outgassing: The gaseous emission or de-aeration from a PCB or solder joint.

Overcoat:   A thin film of insulating material, either plastic or inorganic (e.g., glass or silicon nitride) applied over integral circuit elements for the purposes of mechanical protection and prevention of contamination.

Overglaze: A glass coating that is over another component or element, normally for physical protection or electrical isolation purposes.

Overlap: The contact area between a film resistor and a film conductor.

Oxide Content: The amount of oxides present on the surface of solder powder.

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P

Package: The container for an electronic component(s) with terminals to provide electrical access to the outside of the container. In addition, the container usually provides environmental protection (hermeticity), and a defined form factor.

Package Cap: The cup-like cover that encloses the package in the final sealing operation.

Packaging Density:   The quantity of components, interconnections, and mechanical devices per unit volume.

Package Lid:  flat cover plate that is used to seal a package cavity.

Packaging Level:   The various members that comprise the packaging hierarchy, such as chip, chip carrier, PCB, system, etc.

Pad: A metallized area on the surface of an active substrate as an integral portion of the conductive pattern that is typically used for the connection, and/or attachment of components. Also called footprint or land.

Passivation: The formation of an insulating layer directly over a circuit or circuit element to protect the surface from contaminants, moisture, or particles.

Passive Components: (Elements)Elements such as resistors, capacitors, and inductors which do not change their basic character when an electrical signal is applied. Transistors and electron tubes are active components.

Paste: Synonymous with "composition" and "ink" when relating to screenable thick-film materials

Paste Blending: Mixing a resistor paste of different ohms/square value to create a third value in between those of the two original materials.

Paste Soldering: Finely divided particles of solder suspended in a flux paste. Applied by screening on to a film circuit and reflowing. Forms connections to solderable components.

Pattern: The outline of a collection of circuit conductors and resistors that defines the area to be covered by the material on a film circuit substrate.

Peak Firing Temperature: The maximum temperature seen by the resistor or conductor paste in the firing cycle as defined by the firing profile.

PCB: The term generally used for printed circuit configurations such as rigid or flexible, single, double, or multilayered boards that are completely processed. A PCB or PWB is a substrate of a glass fabric impregnated with a resin (ususally epoxy) and cured and clad metal (almost always copper) upon which a pattern of conductive traces is formed to interconnect components.

Peel Strength: A true test of the adhesion between the lead and the bonding pad after it has been soldered. This parameter is determined by peeling the component lead off the bonding pad using special fixturing on a pull tester.

Pick-and-Place: The assembly process in which components are selected and placed onto specific locations of the PCB.

Pinhole: Small holes occurring as imperfections which penetrate entirely through film elements, such as metallization films or dielectric films

Pitch: The center-to-center spacing between pads, rows of bumps, pins, etc.

Placement: The manual, semiautomatic, or automatic placement of a component, device, or chip at its intended position at a given packaging level.

Planarity: Planarity refers to substrate surface flatness. It is another term for board warpage or camber.

Plasma Cleaning: A cleaning process that uses electrically excited gas molecules to remove surface contamination. Most commonly found in applications where extreme cleanliness is required, such as bonding pad preparation on the chip and substrate for wire bonding.

Plastic Encapsulation:   Environmental protection of a completed circuitry embedding it in a plastic such as epoxy or silicone.

Plastic Leaded Chip Carrier (PLCC): A component package with J-leads on all four sides.

Plated Through Hole (PTH): A plated hole in a Substrate used as an interconnection between the top and bottom sides or the inner layers of  that substrate.

Polymerize: To chemically unite two or more polymers or monomers of the same kind to form a molecule with higher molecular weight.

Polymerized Rosin: Rosin that has reacted with itself during the course of a soldering operation.

Potting:  Encapsulating of a circuit in plastic.

Power Density: The amount of power dissipated from a film resistor through the substrate. Measured in W/in2.

Power Dissipation: The dispersion of the heat generated from a film circuit when a current flows through it.

Preflow: The period of time in the reflow profile after preheat and before the reflow spike occurs. During this time, the temperature of the metals being joined is allowed to equalize.

Preheat: A preliminary phase of a process during which the product is heated at a predetermined rate from the ambient temperature to a desired elevated temperature.

Preheating: Increasing the temperature of a material above the ambient temperature to reduce the thermal shock and influence the dwell time during subsequent elevated temperature processing.

Preseal Visual: The process of visual inspection of a completed hybrid circuit assembly for defects prior to sealing the package.

Print and Fire: A term sometimes used to indicate steps in the thick-film process wherein the ink is printed on a substrate and is fired.

Printing Parameters: The conditions that affect the screening operation such as off-contact spacing, squeegee speed, squeegee pressure, etc.

Printed Wiring Assembly: Also called printed circuit assembly, this term is used for a printed wiring board in which all the individual components have been completely attached.

Probe: A rigid, pointed, metallic, wire-shaped device used for making electrical contact to a circuit pad for electrical test purposes.

Production Lot: Hybrid microcircuits manufactured on the same production line(s) by means of the same productions techniques, materials, controls, and design, The production lot is usually date coded to permit control and traceability required for maintenance of reliability programs.

Profile: A graphical representation of the time versus temperature of a continuous furnace or oven cycle.

Pseudoplastic: A fluid that displays a decrease in viscosity with an increase in the shear rate.

Pull Strength: A measure of the quality of a solder joint formed between a component lead and a bonding pad on a substrate. This parameter is typically determined by placing a hook under the shoulder of a lead and pulling up.

Purple Plague: One of several gold-aluminum compounds formed when bonding gold to aluminum and activated by re-exposure to moisture and elevated temperature (<340 deg. C). Purple plague is purplish in color and is very brittle, potentially leading to time-based failure of the bonds. Its growth is highly enhanced by the presence of silicon to form ternary compounds.

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Q

Quad Flat Pack (QFP): A ceramic or a plastic chip carrier in which the leads project down and away from all four sides of a square package.

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R

Reflow: The application of heat to a surface containing a thin deposit of a low melting point metal or alloy (e.g., solder paste tin lead alloy), resulting in the melting of the deposit, followed by its solidification.

Reflow Soldering: A process for joining surface mount parts into a solder paste for permanent interconnection via passage through various stages including preheat, stabilization/drying, reflow spike and cooldown.

Registration: The alignment of a circuit pattern on a substrate.

Registration Marks: The marks used for aligning successive processing masks.

Reliability: The continued conformance of a device or system to a specification over an extended period of time.

Repair: An operation that restores a part or assembly to a condition in which it can be used.

Repeatability: The ability of a process to accurately return to a specific target. A designation for evaluating process equipment and consistency.

Residues: Contaminants left behind on the surface of the substrate or the PCB as a consequence of both preassembly and assembly operations.

Resin Flux: A resin and small amounts of organic activators in an organic solvent.

Resin Impregnation: The process of coating a glass fabric by resin using metering rolls to control the fabric to resin ratio.

Resin: An organic polymer which, when mixed with a curing agent, crosslinks to form a thermosetting plastic.

Resistance: The property of a material to oppose the flow of current.

Resistor Drift: The change in resistance of a resistor through aging and usually rated as percent change per 1000 hr.

Resistor Geometry: The film resistor outline. (see Aspect Ratio)

Resistor Overlap: The contact area between a film resistor and a film conductor

Resistor Paste Calibration: The characterization of a resistor paste for resistivity, TCR and other parameters by screening and firing a test pattern using the paste and recording the results.

Rework: A manufacturing operation that restores a part or an assembly to an operable condition. The reworked part/assembly should meet or surpass specifications.

Rheology: The study of the change in the form and flow of matter, embracing elasticity, viscosity, and plasticity.

Rosin Flux: Rosin in an organic solvent or rosin as a paste with activators.

Rosin: A hard, natural resin, consisting of abietic acid and pimaric acids and their isomers, some fatty acids, and terepene hydrocarbons. Resin is extracted from pine trees and subsequently refined.

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S

Saponifier: An alkaline chemical added to water to improve its ability to dissolve rosin flux residues.

Schematic: Diagram in symbolic form of a functional electronic circuit.

Scored Substrate: A substrate that has been scribed with a thin cut at the break-lines.

Screen: A network of metal or fabric strands, mounted on a frame, and upon which the film circuit patterns and configurations are superimposed by photographic means.

Screen Deposition: The laying down of a circuit pattern on a substrate using the silk screening technique.

Screen Printing: The process whereby the desired film circuit patterns are transferred to the surface of the substrate by forcing material through the open areas of a screen using the wiping action of a soft squeegee.

Scribe Line: A series of laser pulses (normally 4-6 mils apart) typically 35-50% of substrate thickness. Allows for multi-up arrays that are easily snapped into single devices after processing. Tolerance after snapping, +/- 3 mils typical.

Scribed Edge: Somewhat rough edge remaining after snapping. Normally 2-3 mils larger than initial dimension. Most cost effective sizing technique when tolerance permits.

Self-Alignment: The tendency of certain slightly misaligned components (during placement) to self-align with respect to their land patterns during reflow soldering. It occurs due to the surface tension of molten solder.

Serpentine Cut: A trim cut in a film resistor that follows a serpentine or wiggly pattern to effectively increase the resistor length and increase resistance.

Shadowing: The failure of molten solder to wet the leads of surface mount components due to their location on the board during wave soldering or the cause for insufficient heating of surface mount components due to their location on the board during infrared reflow soldering.

Shear Strength: The force required to shear apart adhesive-bonded and cured materials and/or components.

Sheet Resistance: The electrical resistance of a thin sheet of a material with uniform thickness as measured across opposite sides of a unit square pattern. Expressed in ohms/square.

Short: An unwanted connection between conductor paths.

Silk Screen: A screen of a closely woven silk mesh stretched over a frame and used to hold an emulsion outlining a circuit pattern and used in screen printing of film circuits. Used generically to describe any screen (stainless-steel or nylon) used for screen printing.

Silver chromate test: A qualitative check for the presence of ionic halides in RMA fluxes.

Single-Layer Board: A printed circuit board that contains metallized conductors on one side of the board only.

Slump: A spreading of material (solder paste, adhesive,thick film, etc.) after stencil printing (or dispence) but before curing.

Small Outline Integrated Circuit (SOIC): An integrated circuit surface mount package with two parallel rows of gull-wing leads.

Small Outline J-Leaded (SOJ): An integrated circuit surface mount package with two parallel rows of J-leads.

Small Outline Transistor (SOT): Discrete surface mount transistors with a molded plastic outline that serve small and medium power applications.

Snapback: The return of a screen or stencil to normal (flat plane) after its deflection by a squeegee across its surface.

Solder Balls: Small spheres of solder adhering to the laminate, mask, or conductor surfaces usually after wave or reflow soldering.

Solder Bridging: Solder paste or solder on two or more adjacent pads that come into contact to form a conductive path (forming a bridge).

Solder Bumps: Round solder balls bonded to the pads of components and subsequently used for face-down bonding techniques.

Solder Connection: The joining of two or more metal parts by means of an electrical or mechanical connection.

Solder Mask: A dielectric material used to cover the entire surface (except where the joints are to be formed) of the PCB primarily to protect the circuitry from environmental damage. Solder mask also helps to reduce bridging.

Solder Paste: A homogenous and kinetically stable mixture of minute spherical solder particles, flux, solvents and binder that is screen printed onto the printed circuit board and then reflowed to form the solder joints.

Solder Powder: The solder alloy in solder paste exists in the form of powder. Solder powder is the major ingredient that affects the printability of the paste and the quality of the solder joint.

Solder Thickness: The amount of solder deposited on a pad for reflow. Optimum thickness will vary with pad size and pitch, but must be consistent across a single bonding site.

Solder Wicking: The capillary movement of molten solder onto a pad or component lead or between metal surfaces, such as strands of wire.

Solder: A low melting point alloy, usually of lead (Pb) and tin (Sn), that can wet copper, conduct current, and mechanically join conductors.

Solderability: The ability of a conductor to be wetted by solder and to form a strong bond with the solder.

Solder Dam: A dielectric composition screened across a conductor to limit molten solder from spreading further onto solderable conductors.

Soldering: A process of joining metallic surfaces with solder, without melting the base material.

Solids Content: The metal powder content as a percentage of the mass of the wet solder paste, or the percentage by weight of rosin in a flux formulation.

Solvent Cleaning: A cleaning method employing chlorinated and fluorinated hydrocarbon liquids.

Solvent: A solution capable of dissolving a solute.

SPC: The use of statistical techniques to analyze the outputs of processes with the results guiding actions taken to adjust and/or maintain a state of quality control.

Specific Heat: The ratio of a material's thermal capacity to that of water at 15ºC.

Spherically Compliant Suspension: A patented mechanism based on a four-bar linkage that can be integrated into an outer lead bonder to have self-planarization of the thermode head to the substrate. This mechanism has been developed and patented by Universal Instruments Corporation.

Spread: The distance a substance (e.g., an adhesive) moves after it has been applied at ambient conditions.

Squeegee: The rubber or metal blade of a screen printer that pushes the composition across the screen or stencil and through the patterned apertures and onto the substrate.

Stainless Steel Screen: A stainless steel mesh screen stretched across a frame and used to support a circuit pattern defined by an emulsion bonded to the mesh.

Step and Repeat: A process wherein the conductor or resistor pattern is repeated many times in evenly spaced rows onto a single film or substrate.

Stencil Printing: Deposition of a specific material, such as solder paste, using a stencil.

Stencil: A metal mask in which patterns or apertures matching the component locations on the PCB are made so a suitable material can be forced through the apertures by a squeegee onto a substrate. Common materials are stainless steel and brass.

Storage life: The period that an adhesive can be stored and remain viable for use.

Substrate Geometry: Substrate dimensions, typically dimensions critical to implement a successful bonding process, including the following: board size, bonding pad layout and dimensions, solder thickness, adjacent components, planarity, fiducial shape and dimensions, and board thickness and construction.

Surface Mount Device (SMD): An active or passive device designed to be soldered to the surface of the printed circuit board.

Surface Mount Technology (SMT): A method of assembling printed circuit boards where the components are mounted onto the surface of the board rather than being inserted into holes in the board.

Surface Tension: An effect of the forces of attraction between the molecules on the surface of a liquid. Surface tension is the reason water beads up better on the hood of your car when waxed versus unwaxed. The wax increases the surface tension of the water, and thus it beads up more readily.

Surfactant: A chemical added to any substance to lower its surface tension.

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T

Tackiness: The ability of solder paste to hold surface mount components in place after placement but before reflow soldering.

Tape-and-reel: Component packaging for placement via housing parts in cavities in a continuous strip. The cavities are covered by a plastic tape so that they can be wound in a reel for presentation to a component placement machine.

Tape Bonding: Utilization of a metal or plastic tape material as a support to a carrier of a component in a gang bonding process.

Tantalum Capacitor: Capacitors that utilize a thin tantalum oxide layer as the dielectric material

Temperature Coefficient of Capacitance (TCC): The amount of capacitance change in a capacitor with temperature. Expressed as the average change over a certain temperature range in ppm/degree C

Temperature Coefficient of Resistance (TCR):  The amount of resistance change in a resistor (or resistor material) with temperature. Expressed as the average change over a certain temperature range in ppm/degree C.

Temperature Cycling: An environmental test where the device under test is subjected to several temperature changes from a low temperature to a high temperature over a certain period of time.

Tensile Strength: The longitudinal stress required to break a prescribed specimen divided by the original cross-sectional area at the point of rupture (usually expressed in lbs. per square inch or PSI).

Terminal: A metallic device used for making electrical connections.

Test Board: A printed circuit board deemed to be suitable for determining the acceptability of a group of boards produced with the same fabrication process.

Test Fixture: A device that interfaces between test equipment and the unit being tested.

Test Pattern: A pattern used for inspecting or testing purposes.

Test Point: A specific point of access to an electrical circuit used for electrical testing purposes.

Thermal Conductivity: The rate with which a material is capable of transferring a given amount of heat.

Thermal Cycling: A method used to induce stresses on electrical components by means of sequential heating and cooling in an oven. It is used in accelerated reliability testing.

Thermal Profile: A time versus temperature graph that displays the temperatures an assembly is subjected to over time in an oven during processes such as reflow soldering or the curing of adhesives, encapsulants, and conformal coatings.

Thermal Shock: A condition whereby devices are subjected alternately to extreme heat and extreme cold; used to screen out processing defects.

Thermocompression Bonding: The joining of two materials without an intermediate material by the application of pressure and heat in the absence of electrical current.

Thermocouple: A sensor made of two dissimilar metals which, when heated, generate a small DC voltage used in temperature measurements.

Thermoplastic: Polymer materials that can be repeatedly melted without significant change in their properties.

Thick Film: A film deposited by screen printing "paste" and subsequent firing at high temperature to fuse the paste into its final form.

Thick Film Hybrid Circuit: A hybrid microcircuit that has add-on components, usually chip devices, added to a thick film network to perform an electrical function.

Thick Film Technology: The technology whereby electrical networks or elements are formed by applying a semi-liquid paste coating through a screen of mask in a selective pattern onto a supporting substrate material and fired.

Thin Film: A thin film (usually less than 100 um thickness) isone that is deposited onto a substrate by an accretion process such as vacuum evaporation, or pyrolytic decomposition, or sputtering.

Thixotropic Ratio: An indication of thixotropy as a ratio of viscosities at two different shear rates.

Thombstoning: A soldering defect in which a chip component is pulled into a vertical position leaving one side unsoldered.

Threshold Limit Value: A guideline for the exposure of humans to solvents; it is expressed as a Time Weighted Average (TWA) of the parts per million of vapor in air.

Through Hole: A hole in the substrate connecting the two surfaces of a printed circuit structure.

Tinning: The process of coating metallic surfaces with a thin layer of solder.

Tip-to-Tip Dimension: With respect to component geometry, the distance between the ends of the leads on opposite sides of a component after excising and forming.

Tombstoning: The lifting of one end of a passive surface mount component during solder reflow caused by surface tension and unbalanced forces of solder wetting.

Top Hat Resistors: Film resistors having a projection on one side allowing a notch to be cut into the center of the projection to form a serpentine resistor and thereby increase the resistivity.

Torsional Strength: The torque required to separate adhesive bonded (and cured) materials and/or components.

Touch-Up: The identification and elimination of defects in a product.

Tracking: Two similar elements on the same circuit that change values with temperature in close harmony are said to track well. Tracking of different resistors is measured in ppm/deg C (difference). Tracking is also used in reference to temperature hysteresis performance and potentiometer repeatability.

Transistor: An active semiconductor device capable of providing power amplification. Transistors have three or more terminals.

Trimming: Notching a resistor by abrasive or laser means to raise the nominal resistance value.

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U

Ultra-fine-pitch: Center-to-center lead distances and conductor spacings of 0.010" or less.

Ultrasonic Bonding: A process involving the use of ultrasonic energy and pressure to join two materials.

Ultrasonic Cleaning: A method of cleaning that uses cavitation in fluids caused by applying ultrasonic vibrations to the fluid.

Underfill: In flip chip applications, the material injected under the die after testing to ensure reliability. This material is particularly important for flip chips mounted on substrates with different CTEs than silicon, such as FR-4 and some ceramics.

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V

Vapor Phase Reflow: A solder reflow technique in which the solder joints are heated by the condensation of an inert vapor.

Vehicle: A thick film term that refers to organic system in the screenable paste

Via: An opening in the dielectric layer that interconnects different layers of circuitry. A via can be used for an electrical connection or for thermal dissipation.

Void: A cavity inside the solder joint formed by gases released during reflow or by flux residues entrapped before solidification.

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W

Waffle Pack: A matrix tray for holding bare die. Typically, waffle packs are 2" x 2" or 4" x 4." The pockets for die in waffle packs are typically designed for specific die sizes; they are not standardized.

Wave Soldering: A process in which many potential solder joints are brought in contact with a wave of molten solder for a short period of time and are soldered simultaneously.

Wetting: The spreading of solder along the leads and pad to produce complete and uniform solder coverage.

Whisker: A metallic growth, needle-like in size, that appears on the surface of a PCB.

Wedge Bond: A bond made with a wedge tool. The term is usually used to differentiate thermo-compression wedge bonds from other thermo-compression bonds (almost all ultrasonic bonds are wedge bonds).

Wire Bonding: The use of fine wires to connect semiconductor packages to the next level of packaging. Wires are composed of gold or aluminum.

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Y

Yield:   The ratio of usable components at the end of a manufacturing process to the number of components initially submitted for processing. Can be applied to any input-output stage in processing, and so must be carefully defined and understood.

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Z

Z-Axis Conductive Epoxy: Refer to anisotropic conductive adhesive.

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