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The distance between points of corresponding phase of two consecutive cycles of a wave. The wavelength is related to the propagation velocity, and the frequency. It is indirectly proportional to frequency.

Wavelength Isolation

A WDM’s isolation of a light signal in the desired optical channel from the unwanted optical channels. Also called far-end crosstalk.


The thorough impregnation of a material by a liquid. The more viscous a fluid, and the higher its surface tension, the more difficult it is for the liquid to “wet” materials. Certain additives, for example, water softeners, reduce surface tension, or viscosity and improve wetting properties, allowing the material to flow out more.

Wetting Balance

An instrument used to measure wetting forces, and consequently, estimate solderability.


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

Wire Bonding

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

Working life

The period of time during which an epoxy after mixing with a curing agent, remains workable and suitable for use.

Yield Strength

The load in pounds per square inch where the material under test begins to change dimensions and will not completely recover when the load is removed. Yield strength will normally be lower than ultimate strength. Generally speaking, the more rigid a material is, the closer will be yield and ultimate strengths. Furthermore, the more resilient a material is, the greater the spread between yield and ultimate strengths.


A device that includes a source and driving electronics. It functions as an electricalto-optical converter.


Underwriter’s Laboratory.

Ultrasonic Cleaning

The use of ultrasonic energy along with a chemical solvent to clean a component or a PCB assembly immersed in solvent. Mechanical oscillation is introduced by the ultrasonic energy to facilitate cleaning.


The invisible region of the spectrum just beyond the violet end of the visible region. Wavelengths range from 1 to 400 nm.


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.


Operating in one direction only.




Volt. Unit of eletric potential, also known as electromotive force. Represents the potencial difference between two points of a conducting wire carrying a constant current of 1 ampere when the power dissipated between these points is equal to 1 watt.


Drilled holes in laminate that interconnect different layers of circuitry. Vias can be used for electrical connections or thermal dissipation.


The property of resistance to flow exhibited within the body of a fluid. Usually measured in centipoise.

Visible Light

Electromagnetic radiation visible to the human eye; wavelengths of 400-700 nm.

Visible Spectrum

Light which can be seen by the unaided human eye, defined in our case as between 400 nm and 750 nm.


A hole or bubble in a solder joint.


See Watt.

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.


See wide area network.


Linear measurement of optical power, usually expressed in milhwatts, microwatts, and nanowatts.

Wave Cleaning

Cleaning a PCB by passing it through a wave of solvents (similar to the concept used in a wave fluxer or a wave soldering process).

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.


A system or material designed to confine and direct electromagnetic waves in a direction determined by its physical boundaries.

Tape Bonding

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


Abbreviation for thermoelectric cooler.

Temperature, Curing

The temperature to which an adhesive or an assembly is subjected to cure the adhesive. Note-The temperature attained by the adhesive in the process of setting it may differ from the temperature of the atmosphere surrounding the assembly.

Tensile Strength

The pulling force necessary to break a given specimen divided by the cross sectional area. Units given in lbs./in/2 (P.S.I.). It measures the resistance of a material to stretching without rupture. Normally is not used with reference to elastic materials which recover after elongation.


A metallic device used for making electrical connections.

Test Pattern

A pattern used for inspecting or testing purposes.

Thermal Conductivity

A measure of how rapidly heat is conducted through a material.

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 Noise

Noise resulting from thermally induced random fluctuation in current in the receiver’s load resistance.

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 Resistance

The ability of a cured system to resist cracking or crazing under conditions of rapid and continuous thermal change. The 1/4 inch Olyphant Washer test is cycled over a temperature range of -55¡C to +125¡C, this temperature is normally used as the test condition unless otherwise stated.

Thermocompression Bonding

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


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


Describes the property of an epoxy, to set or become rigid and non-meltable when heated with or without pressure.

Thermosetting Plastic

Polymer materials that cure (irreversably polymerize) at specific temperature and time conditions.

Thixotropic Ratio

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


The property of a paste or fluid to thicken or set up to a paste or semi-gel when allowed to stand. Agitation breaks it down but further standing will again permit a viscosity rise.

Torsional Strength

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


A device that performs, within one chassis, both telecommunicafion transmitting and receiving functions.


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

Solvent Cleaning

A cleaning method employing chlorinated and fluorinated hydrocarbon liquids.

Solvent Extraction

The removal of one or more components from a liquid mixture by intimate contact with a secondary liquid that is nearly insoluble in the first liquid and which dissolves the impurities and not the substance to be purified.

Specific Gravity

The ratio of the weight of any volume of a mass or substance to the weight of an equal volume of water at given temperature. The specific gravity of a substance times the density of water equals the density of the substance.

Specific Heat

The ratio of a material’s thermal capacity to that of water at 15°C.


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


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.

Stencil Printing

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

Storage life

The period of time during which a packaged epoxy or curing agent can be stored under specific temperature conditions and remain stable for use. Sometimes called shelf life.


An applied force or pressure, as tension or shear, exerted on a body which produces a resultant strain on the material. The ability of material to withstand a stress depends on the strength of its cohesive force or molecular resistance.


A material upon the surface of which an epoxy is spread for any purpose, such as bonding or coating.

Substrate Geometry

Substrate dimensions, typically dimensions critical to implement a successful bonding process, including the following

Surface Mount Technology

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 Resistivity

The resistance to a current flow along the surface of an insulator material. Measure in ohms-cm.

Surface Tension

The property of a liquid which causes the surface to pull into the smallest area for a maximum volume, hence, drops are spherical. The fact that water drops on a wax surface do not spread out due to surface tension. If a wetting agent were to be added to the water the round droplet would spread out into a film because of the lowered surface tension.

Surface-Emitting Diode

An LED that emits light from its flat surface rather than its side. Simple and inexpensive, with emission spread over a wide angle.


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

T Tera.

One trillion.

TAB Component

An IC mounted on a TAB site.

Tape Automated Bonding (TAB)

The process where silicon chips are joined to patterned metal traces (leads) on polymer tape to form inner leads bonds and subsequently the leads are attached to the next level of the assembly, typically a substrate or board, to form outer lead bonds. TAB is the technique of interconnecting silicon with beam bonding as opposed to wire bonding.

Tape Ball Grid Array (TBGA)

A BGA package on a copper polyimide base like TAB, except TAB leads are replaced by an area array ball grid for interconnects. A stiffener is added to ensure flatness for the mass reflow assembly process.


Abbreviation for second.


Society of Automotive Engineers.


The change of direction of light rays or photons after striking small particles. It may also be regarded as the diffusion of a light beam caused by the non-homogeneity of the transmitting material.

Screen Printing

The transfer of a pattern onto a surface by forcing a suitable material through a screen with a squeegee.


To convert an epoxy into a fixed or hardened state by chemical or physical action through polymerization.

Shear Strength

The shear force required to break a specimen divided by its cross-sectional area; the force being applied parallel to the cross-sectional area.

Shore A Hardness

The reading of a material’s hardness on a durometer, the scale of which is 0-100, used on elastomers and other flexible materials. Consists of a pin point depression into the material, the material being at least 100 mils thick. A Shore A reading of 80 equal a Shore D reading of 30.

Shore D Hardness

The reading of a material’s hardness on a durometer similar to the Shore A durometer, the scale of which 0-100, used on rigid and semi-rigid materials. Consist of a pin point depression into the material. Both the Shore A and Shore D instruments are made by the Shore Instrument Manufacturing Company, Inc., Jamaica, NY.


An unwanted connection between conductor paths.


The decrease in volume, or contraction, of a material by the escape of any volatile substance, or by a chemical or physical change in the material.

Si Silicon

Generally used in detectors. Good for short wavelengths only (e.g., < 1000 nm).

SI Units

Abbreviation for International System of Units, commonly known as the metric system,

Silica Glass

Glass made mostly of silicon dioxide, SiO2, used in conventional optical fibers.


(SM) Fiber A small-core optical fiber through which only one mode will propagate. The typical diameter is 8-9 microns


The distance a substance (e.g., an adhesive) moves after it has been applied and cured.


Surface-mount device.


Surface-mount technology.

Softening Range

The range of temperature in which a thermoplastic changes from a rigid to a soft state.

Solids Content

The metal powder content as a percentage of the mass of the wet solder paste.


A solution capable of dissolving a solute.


Similar to encapsulating, except that steps are taken to insure complete penetration of all the voids in the object before the resin polymerizes.


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.


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.


Partially-cured fiber-reinforced resin fabric. Also referred to as the B-stage in the manufacturing of PCB.


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


(Picosecond ) One trillionth of a second.


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.


(Picowatt) One trillionth of a Watt.

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.


The combined process of emission, transmission, and absorption of thermal energy between bodies separated by an empty space.


An instrument, distinct from a photometer, to measure power (Watts) of electromagnetic radiation.


A terminal device that includes a detector and signal processing electronics. It functions as an optical-to-electrical converter.

Refractive Index

Gradient The change in refractive index with distance from the axis of an optical fiber.


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


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


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


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


The ability of a material to resist passage of electrical current either through its bulk or on a surface. The unit of volume resistivity is the ohm-cm, of surface resistivity, the ohm.


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


Printed circuit board.

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.


A two-electrode, radiation-sensitive junction formed in a semiconductor material in which the reverse current varies with illumination. ItÕs a semiconductor device that converts light to electrical current. Photodiodes are used for the detection of optical power and for the conversion of optical power to electrical power.


The technology involving light and photons at all wavelengths between the far-infrared and the ultra-violet. Also called “Optoelectronics”.


Providing an electric current under the influence of light or similar radiation.


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


The fine solid particle, usually inorganic, used in the preparation of colored products, and substantially insoluble in the vehicle. In contrast, a dye is soluble.


Small regular or irregular crater in a surface, usually with its width approximately of the same order of magnitude as its depth.


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

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 Deformation

With respect to materials science, the deformation of a material resulting from it being stressed beyond its ability to return to its original shape.

Plastic Fiber

An optical fiber having a plastic core and plastic cladding.

Plating Inconsistency

Variance in overall lead plating thickness and cross-sectional characteristics, which can cause lead form variation during the lead forming process.

Polar Solvent

A solvent with the ability to dissolve polar compounds such as inorganic salts. However, polar solvents cannot dissolve nonpolar compounds such as resins and hydrocarbons.


The direction of the electric field in the lightwave.

Polarization Maintaining Fiber

Fiber that maintains the polarization of light that enters it.

Polarization Mode Dispersion

(PMD) Polarization mode dispersion is an inherent property of all optical media. It is caused by the difference in the propagation velocities of light in the orthogonal principal polarization states of the transmission medium. The net effect is that if an optical pulse contains both polarization components, then the different polarization components will travel at different speeds and arrive at different times, smearing the received optical signal.


Thermosetting ring chain polymers characterized by -NH group. They are being increasingly used as dielectrics in high performance circuits.


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

Pot Life

The length of working time of a two component reactive system from the time of the addition of the curing agent in a specific mass (i.e. 100 grams). It is expressed in minutes.


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


Nanometer. One billionth of a meter.


Refer to “nonpolar.”


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

Nonpolar Solvent

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


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.


Nanowatt. One billionth of a Watt.


Any material is opaque if no light can be transmitted through it.

Operating Or Service Temperature

The temperature at which an epoxy system can operate continuously without degradation of its properties.

Optical fiber

A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote internal reflection. It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.

Optical Waveguide

Another name for optical fiber.


That branch of physical science concerned with vision and certain phenomena of electromagnetic radiation in the wavelength range extending from the vacuum ultraviolet at about 40 nm to the far-infrared at 1 mm. Now being replaced by the more inclusive term photonics.


Uneven surface somewhat resembling an orange peel.

Organic PCB

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


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

p Pico

One trillionth.

Packaging Density

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

Packaging Level

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


A portion of the conductive pattern that is typically used for the connection, and/or attachment of components.

PBGA (Plastic Ball Grid Array)

Generic name for a BGA component constructed on organic substrate material, such as FR-4, overmolded with plastic.


One millionth of a meter. Abbreviated um.


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.


One millionth of a second. Abbreviated us.


One millionth of a Watt. Abbreviated uW


Military specification.


Military standard.


One thousandth of an Amp.


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


Abbreviation for multimode.


Any ingredient added to an epoxy formulation that changes its properties.

Moisture Resistance

Having some resistance to high humidity. A moisture resistant adhesive will not be easily affected by moisture. Will not easily change its chemical and physical properties due to moisture. Should not be confused with “water proof.”

Mold Flash

Plastic debris remaining on a plastic molded package after the component manufacturing process. This can occur on molded carrier ring (MCR) and plastic quad pack (PQFP) components.


( Milliseconds) One thousandth of a second.

Multimode Fiber

An optical fiber that has a core large enough to propagate more than one mode of light The typical diameter is 62.5 micrometers.

Multimode Laser Diode

(MMLD) Synonym for Multilongitudinal mode laser.


Millivolt. One thousandth of a Volt. mW Milliwatt. One thousandth of a Watt.

n Nano

One billionth.

N Newtons

Measure of force generally used to specify fiber optic cable strength.


National Electrical Manufacturers Association.

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.

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.


Light Emitting Diode. LEDs work on the principle of spontaneous emission of light as opposed to stimulated emission. LEDs usually have high bandwidth but relatively low power. LEDs operate in the infrared, visible and ultraviolet regions of the optical spectrum.


Synonym optical fiber.


The amount of a signal’s power, expressed in dB, that is lost in connectors, splices, or fiber defects.

M Mega

One million.

M Meter

The SI base unit of length, approximately 39.37 inches.

Material Dispersion

Dispersion resulting from the different velocities of each wavelength in a material.

Maximum Service Temperature

Highest recommended continuous use temperature based upon thermal endurance and historical data.

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. For example, a 325 mesh screen has 325 openings per inch.

Metal-Core Boards

Boards built with a metallic core and an organic or inorganic insulation on either sides of the core. The core could be made of steel, stainless steel, aluminum, copper, or a laminate of metals (in most cases copper invar copper or copper tungsten copper). The insulation of the core is done prior to metallization.


(MegaHertz) One million Hertz (cycles per second).


See integrated systems digital network.


International Standards Organization.

Isotropic Conductive Adhesive (ICA)

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).

Izod Impact Strength

A measure of the brittleness of a material. Brittle materials will have low izod impact values (.15 for example). Tough materials will have high izod impact strengths (.60 for example).

K Kelvin

Measure of temperature where water freezes at 273° and boils at 373°.

k Kilo

One thousand.


A very strong, very light, synthetic compound developed by Du Pont which is used to strengthen optical cables.


(Kilogram) Approximately 2.2 pounds.


One thousand cycles per second.


(Kilometer) 1km = 3,280 feet or 0.62 miles.


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


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.


See local area network.

Large Core Fiber

Usually, a fiber with a core of 200 um or more.


Acronym for light amplification by stimulated emission of radiation. Lasers usually have low bandwidth and high power. Lasers in fiber optics are usually solid-state semiconductor types.

Laser Diode

A semiconductor that emits coherent light when forward biased.


The process during which liquid solder dissolves a metal coating.


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

Lead (Pb)

A soft heavy gray metal used in solder and other alloys.

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.


A property of absorbing and holding moisture.


See Hertz.


Institute of Electrical and Electronic Engineers.


To fill the voids and spaces of an electrical unit with a compound. (This does not imply complete fill or complete coating of the surfaces by a hole-free film).

In-Circuit Test

An electrical test of a PCB assembly in which each component is tested individually, even though many components are soldered to the PCB.

Index of Reftaction

(Also refractive index) The ratio of the velocity of light in free space to the velocity of light in a fiber material. Symbolized by n. Always greater than or equal to one.

Index-Matching Fluid

A fluid whose index of refraction nearly equals that of the fiber’s core. Used to reduce Fresnel reflection at fiber ends. See also index-matching gel.

Index-Matching Gel

A gel whose index of refraction nearly equals that of the fiber’s core. Used to reduce Fresnel reflection at fiber ends. See also index-matching fluid.

Inert Atmosphere

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


(IR) The invisible portion of the electromagnetic spectrum bounded by the long-wavelength extreme of the visible spectrum (about 0.7 um) and the shortest microwaves (about 1000 um). See also frequency, light.


(Indium gallium arsenide) Generally used to make high-performance long-wavelength detectors.


(Indium gallium arsenide phosphide) Generally used for long-wavelength light emitters.

Injection Molded Boards

Printed circuit boards made by molding filler-reinforced resins into a desired shape. Routing and through hole metallizations are performed by seeding and plating, or by printing. An alternative approach is to transfer mold the interconnect directly onto the injection molded cards.

Insertion Loss

The loss of power that results from inserting a component, such as a connector or splice, into a previously continuous path.

Insulation Resistance

The ratio of the direct voltage applied to electrodes in contact with an epoxy system to the total current between them. It is dependent upon both the volume and surface resistance of the epoxy systems. ASTM D257-61.


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.


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


See infrared.


Instrument Society of America.


(Gallium indium arsenide phosphide) Generally used for long wavelength light emitters.

Gardner Color Scale

A system of color standards based upon stable solutions of ferric chloride used in the evaluation of resins, lacquers, oils and varnishes. The Gardner Scale can be correlated roughly with other color standards such as FAC, ASTM, NPA and Lovibond.

Ge Germanium

Generally used in detectors. Good for most wavelengths (e.g., 800-1600 nm).


The initial jelly-like solid phase that develops during the transition from a liquid to a solid. Note- In this state the epoxy is soft, flexible, and has no strength.


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.


(Gigahertz) One billion Hertz (cycles per second) or 109 Hertz.

Glass Fiber

Glass Fiber is the original FiberOptic material, and still the standard in communications technology. Glass fiber requires a large bend radius and is not easily field-terminated. Lightly Expressed does not typically use glass fiber. See Acrylic Fiber.

Glass Transition Temperature (Tg)

Approximate midpoint of the temperature range over which a material undergoes a phase change from brittle to rubbery or vice versa.


That property of the cured epoxy or any other material which causes it to reflect light.

Green Strength

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


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


A substance or mixture of substances added to an epoxy resin to promote or control the curing reaction by taking part in it.

Heat Distortion (Deflection) Temperature

The temperature at which a material softens enough to distort under a given load. It is not usually considered to be beyond the maximum usable temperature, but is an indication of the maximum usable temperature when the material is load bearing at a given load. As the load decreases, the maximum usable temperature will increase.

Heat Sink

Any device that absorbs and draws off heat from a hot object, thereby neutralizing the extreme temperature.


The sealing of an object so it is airtight.


One cycle per second.

Humidity (Absolute)

The amount of moisture present in the atmosphere expressed in grams per cubic meter.

Humidity (Relative)

The ratio of the amount of moisture contained in the atmosphere to the amount of moisture that can be carried in the atmosphere at a given temperature. Relative humidity is expressed in percent, e.g., 75% R.H. at a given temperature means that the air is 75% saturated with moisture.

Hydrophilic Solvent

Refer to “polar solvent.”

Hydrophobic Solvent

Refer to “nonpolar solvent.”


Small globular mass which has not blended completely into the surrounding material and is particularly evident in a transparent or translucent material.


Rate Number of device failures in one billion device hours.

Flame Retardance

The ability of an epoxy system to resist combustion or burning. Some materials tend to extinguish themselves when subjected to a flame. Such materials are classified as self-extinguishing. ASTM D790-63.

Flash Point

The temperature at which the material gives off flammable vapor in sufficient quantity to ignite momentarily on the application of a flame under specified conditions.

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.

Flexural Modulus

The ratio, within the elastic limit, of flexural stress to the corresponding strain. It is expressed in pounds per square inch. ASTM D790-63.

Flexural Strength

Ability of a material to withstand failure due to bending.

Flip Chip

Any packaging scheme in which the active circuitry of an IC is placed facing the surface of the substrate. Examples are flip TAB and C-4.


Movement of the epoxy during the curing stages before completely cured.

Foot Length

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

Forced Drying Temperatures

A temperature between room temperature and 150°F.(65°C).


See fiber optic test procedure.

Functional Test

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

Fused Coupler

A method of making a multimode or single-mode coupler by wrapping fibers together, heating them, and pulling them to form a central unified mass so that light on any input fiber is coupled to all output fibers.

Fused Fiber

A bundle of fibers fused together so they maintain a fixed alignment with respect to each other in a rigid rod.


Capable of being melted or fused together by melting

G Giga

One billion.


(Gallium aluminum arsenide) Generally used for short wavelength light emitters.


(Gallium arsenide) Used in light emitters.

Gallon, U.S

A volume equal to 231 cubic inches measured at 25°C. (77°F).


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 183°C.


The removal of entrained air from an epoxy system by vacuum. Also referred to as degassing.


Eletric Vehicle.


The liberation of heat energy during a chemical reaction. Exotherm is increased in large masses.

F Fahrenheit

Measure of temperature where water freezes at 32° and boils at 212°.


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

Failure Rate

The number of failures of a device per unit of time.

Failure, Adhesive

The failure at the bond line between substrates and an adhesive; the adhesive separating entirely from the substrate.

Failure, Cohesive

Failure within the adhesive under a stress, resulting in a broken bond with all adhered surfaces still covered with adhesive.

Failure, Substrate

The failure of the substrate material itself, upon subjecting bonded adhered surfaces to a stress.

Faraday Effect

A phenomenon that causes some materials to rotate the polarization of light in the presence of a magnetic field parallel to the direction of propagation. Also called magneto-optic effect.


A rigid tube that confines or holds a fiber as part of a connector assembly.

Fiber Bundle

Refers to the collection of individual fibers that supply light to the fixture. These fibers are held together and protected by the sheathing.

Fiber Optic Cable

A cable containing one or more optical fibers.

Fiber Optic Gyroscope

A coil of optical fiber that can detect rotation about its axis.

Fiber Optic Test Procedure

(FOTP) Standards developed and published by the Electronic Industries Association (EIA) under the EIA-RS-455 series of standards.


(variously “fiber optic,” “fibre optic” (England), and “fiberoptic,”) Refers to the conduction of light waves through materials of exceptional clarity and across long distances. FiberOptics demonstrate total internal reflection by combining like materials of differing indices of refraction.


A substance, often inert, added to a system to improve properties and/or decrease cost.

Filler Materials

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

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.


A material which at room temperature can be stretched repeatedly to at least twice its original length and, upon immediate release of the stress, will return with force to its approximate original length.


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.


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

Electrolytic Corrosion

Corrosion by means of electrochemical action.

Electromagnetic Interference

(EMI) Any electrical or electromagnetic interference tha causes undesirable response, degradation, or failure in electronic equipment. Optical fibers neither emit nor receive EMI.

Electromagnetic Radiation [EMR)

Radiation made up of oscillating electric and magnetic fields and propagated with the speed of light. Includes gamma radiation, X-rays, ultraviolet, visible and infrared radiation, and radar and radio waves.

Electromagnetic Spectrum

The range of frequencies of electromagnetic radiation from zero to infinity.


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.


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

Elongation (%)

Ability of a material to stretch or become longer.


Abbreviation for electromagnetic.


Electromagnetic interference.


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.


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


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


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


A fiber optic bundle used for imaging and viewing inside the human body.


A thermosetting polymer containing the oxirane group.

Epoxy Resin

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

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.


Nonconducting material used to encapsulate circuitry and in the manufacture of capacitors and printed circuit boards.

Dielectric Constant

When electrical energy is applied in a circuit, the insulating material of the electrical charge and releases it when the current is broken. Capacitance is the ratio of charge absorbed to the potential (voltage applied). Dielectric Constance is the ratio of an insulator’s capacitance to that of dry air. (1.0). A dielectric constant of 5 means an insulator will absorb 5 times more electrical energy than air.

Dielectric Strength

The voltage which an insulating material can withstand before breakdown occurs, expressed in volts per Mil

Diffraction Grating

An array of fine, parallel, equally spaced reflecting or transmitting lines that mutually enhance the effects of diffraction to concentrate the diffracted light in a few directions determined by the spacing of the lines and by the wavelength of the light.


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.


Fluid characterized by an increase in viscosity with an increasing shear rate.


A reactive or non-reactive additive whose primary function is to lower the viscosity and extend the material to which it was added.


An electronic device that lets current flow in only one direction. Semiconductor diodes used in fiber optics contain a junction between regions of different doping. They include light emitters (LED’s and laser diodes) and detectors (photodiodes).

Direct Chip Attach (DCA)

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

Direct Chip Attach Module (DCAM)

A component type developed by IBM¨ consisting of a small substrate with flip chips attached using the DCA process. This small substrate, or module, is now a component with solder pads on the bottom side that can be mounted to a board using conventional surface mount processes.


Any change from an initial color possessed by a material, either due to environmental or internal conditions.

Dispensing Supplies

Medium used to apply epoxy to pieces or units. Squeeze bottles, syringes, needles, and meter mix equipment are all examples.


Organic and inorganic phosphates and polymers used in aqueous cleaning to assist in the removal of insoluble particles.

Dissipation Factor

The measure of electrical energy absorbed and lost in the insulating material when energy is applied in a circuit. 20-3060 has a dissipation factor of .01. This means that .01% of the energy being stored (capacitance) is lost. Dissipation factor is the ratio of the resistive component of a capacitor to the capacitive reactance of the capacitor. Also referred to as Loss Tangent. ASTM D150-59T.

Dry Film Photoresist

Solid photoresist applied to a surface by lamination of prefabricated film.

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.

Edge-Emitting Diode

An LED that emits light from its edge, producing more direction output than surface-emitting LED’s that emit from their top surface.


That property of materials by virtue of which they tend to recover their original size and shape after deformation. Note-if the strain is proportional to the applied stress, the material is said to exhibit Hookean or ideal elasticity.

Crosstalk (XT) 1

Undesired coupling from one circuit, part of a circuit, or channel to another. 2. Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates and undesired effect in another circuit or channel.


Cathode ray tube.

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.


To change the physical properties of an epoxy by chemical reaction through polymerization, usually accomplished in the presence of heat and catalyst, alone or in combination.

Cure Cycle

The schedule of time periods at specified temperatures to which a reacting thermosetting plastic or rubber composition is subjected in order to reach certain specified properties.


The process of irreversibly polymerizing a thermosetting plastic by subjecting it to a temperature-time profile.

Curing Agent

A catalytic or reactive agent which when added to resin causes polymerization.

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.


Decibels relative to milliwatt.


Decibels relative to microwatt.


Direct current.

Decibel (dB)

A unit of measurement indicating relative optic power on a logarithmic scale. Often expressed in reference to a fixed value, such as dBm (1 milliwatt) or dBA (1 microwatt).


Any nonconformance to specified requirements by a unit or product.

Deionized Water

Water that has been treated to remove ionized material.


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.


The weight of a material in relationship to its volume.


Dewetting occurs when molten solder has coated a surface and then receded, leaving mounds of solder that are irregularly shaped and are separated by areas covered with a thin solder film.


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

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.

Compressive Modulus

The ratio within the elastic limit of compressive stress to corresponding compressive strain (deformation per original length). It is expressed in pounds per square inch. ASTM D695-54.

Compressive Strength

Crushing load at the failure of a specimen divided by the original sectional area of the specimen.

Compressive Strength, Ultimate

The maximum load in pounds that can be carried per square inch of cross section of the material under test.


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


Having the quality of power of conducting or transmitting heat, electricity, or static electricity.

Conductive Adhesive

Refer to “isotropic/anisotropic conductive adhesives.”


Reciprocal of volume resistivity. Conductance of a unit cube of any material.

Conductor, Electrical

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

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.


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.


The transmission of thermal energy from a hotter region to a cooler region through a moving fluid such as air or water.


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


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


Tying together large molecules and hence changing the physical properties of material. Cross-linking usually involves formation of three dimensional molecular network and is customarily associated with thermosetting resins.


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

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.


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.


Formation of a dry powdery chalk-like appearance or deposit on the surface of a material. It is due to a breaking down of the material after being exposed to ultraviolet light, or other weathering.


The individual circuit or component of a silicon wafer. The 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 chip is directly attached to a printed circuit board or substrate by solder or conductive adhesives.


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


Material that surrounds the core of an optical fiber. Its lower index of refraction, compared to that of the core, causes the transmitted light to travel down the core.


Degree of clearness in a cured epoxy system.


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

Closed-Cell Foamed Plastic

A cellular plastic in which there is a predominance of noninterconnecting cells.


Centimeter. Approximately 0.4 inches.


Complementary metal oxide semiconductor. A family of IC’s. Particularly useful for low speed or low-power applications.


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

Coefficient Of Linear Thermal Expansion

Once cured, a measure of the change in length of an epoxy system over a given temperature range. It is expressed in inches per inch per degree C. ASTM D696-44.

Coefficient Of Thermal Expansion (CTE)

Change in a unit of length or volume that accompanies a unit change in temperature.


The state in which the particles of a single substance are held together by primary or secondary valence forces observed in the tendency of the substance to stick to itself. As used in the adhesive field, the state in which the particles of the adhesive (or the adhered) are held together.


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


Having a refractive index that differs for light of different polarizations.


The smallest unit of information upon which digital communications are based; also an electrical or optical pulse that carries this information.


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


The union of materials by adhesives.

Bond Strength

The unit load applied in tension, compression, flexure, peel, impact, cleavage, or shear, required to break an adhesive assembly with failure occurring in or near the plane of the bond. Note-The term adherence is frequently used in place of bond strength.


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

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.

Brookfield Viscosimeter

An instrument for measuring the viscosity of formulated adhesives under standard conditions of temperature.


Internal void or a trapped globule of air or other gas.


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.


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.

C Celsius.

Measure of temperature where water freezes at 0° and boils at 100°.


The final stage in the reaction of certain thermosetting resins in which the material is relatively insoluble and infusible. Certain thermosetting resins in a fully cured state are in this stage.


One or more optical fibers enclosed within protective covering(s) and strength members.


A thermal unit. A calorie is that amount of heat required to raise the temperature of one gram of water, one degree centigrade.


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.


A substance which markedly speeds up the cure of an adhesive when added in minor quantity as compared to the amounts of the primary reactants.

CD Compact disk

Often used to describe high-quality audio, CD-quality audio, or short-wavelength lasers; CD Laser.


A scale of temperature which features 0° and 100° as the freezing and boiling point of water respectively. To convert centigrade to Fahrenheit multiply by 1.8 and add 32, e.g., (100°C x 1.8) + 32 = 212°F.


1/100th of a poise; (dyne-sec/cm2); a viscosity measurement unit.

Aqueous Cleaning

A cleaning technique that uses water as the primary cleaning fluid.

AR Coating

Antireflection coating. A thin, dielectric or metallic film applied to an optical surfa to reduce its reflectance and thereby increase its transmittance. ArmorA protective layer, usually metal, wrapped around a cable.

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.


A group of elements or circuits arranged in rows and columns on a substrate

Artificial Weathering

The exposure of product to cyclic laboratory conditions involving changes in temperature, relative humidity, and ultra violet radiant energy, with or without direct water spray, in an attempt to produce changes in the material similar to those observed after continuous outdoor exposure. Note-The laboratory exposure conditions are usually intensified beyond those encountered in actual outdoor exposure in an attempt to achieve an accelerated effect.


American standard code for information interchange. A means of encoding information.


Application-specific integrated circuit. A custom-designed integrated circuit.


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


American Society for Testing and Materials.


The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering. Attenuation is usually expressed in dB/km.

Automated Test Equipment

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


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.


An intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated and swells when in contact with certain liquids, but may not entirely fuse or dissolve. The resin in an uncured thermosetting system, is usually in this stage.


The return of a portion of scattered light to the input end of a fiber; the scattering of light in the direction opposite to its original propagation.

Baking Temperature

A temperature above 150°F.(65.6°C). Refers to curing materials at these elevated temperatures.

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.


The range of frequencies over which a particular instrument is designed to function within specified limits.

Bare Board

An unpopulated PCB.

Bend Radius

The smallest radius an optical fiber or fiber cable can bend before increased attenuation or breakage occurs.


Loss Attenuation caused by high-order modes radiating from the outside of a fiber optic waveguide which occur when the fiber is bent around a small radius. See also macrobending, microbending.


Alternating current.


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.


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).

AD or ADC Analog-to-digital converter

A device used to convert analog signals to digital signal.

Additive Plating

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


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


A substance capable of holding materials together by surface attachment.


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


A hard fragmented material used with an epoxy binder as a flooring or surfacing medium. Also coarse filler used as a core for epoxy tools.


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.


A metal formed by combining two or more other metals


Curing agent for epoxy resins that is any of a class of ammonia derivatives. They are derived from Ammonia (NH3).

Analog A continuously variable signal

A mercury thermometer, which gives a variable range temperature readings, is an example of an analog instrument.

Analog Circuit

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

Angular Misalignment

Loss at a connector due to fiber end face angles being misaligned.

Anisotropic Conductive Adhesive ( ACA )

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.


American National Standards Institute.

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