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.

Wavelength

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.

Wetting

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.

Whisker

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.

Visible Spectrum

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

Void

A hole or bubble in a solder joint.

W

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.

WAN

See wide area network.

Transmitter

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

Watt

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

UL

Underwriter’s Laboratory.

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).

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.

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.

Ultraviolet

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