wafer A thin disk (or slice) of silicon on which many separate chips can be fabricated and then cut into individual die.

warp (warpage) The deviation from flatness of a board characterised by an approximately cylindrical or spherical curvature. (Also referred to as ‘bow’ and ‘twist’)

waste hierarchy: The ranking of waste management options in order of sustainability.

waste management: Management of the collection, recovery and disposal of wastes, including options for waste reduction.

waste minimisation: The reduction of waste at source, by understanding and changing processes to reduce and prevent waste. This is also known as process or resource efficiency. Waste minimisation can include the substitution of less environmentally harmful materials in the production process.

wave soldering A method of soldering components to printed circuit boards by moving the boards over a continuously flowing and circulating wave of molten solder in a solder bath. The process permits precise control of the depth of immersion in the molten solder and minimises heating of the board. SMDs are held in place during wave soldering with adhesives and are mounted on the secondary side (wave side) of the PCB.

weave exposure A surface condition of base material in which the unbroken fibres of woven glass cloth are not uniformly covered by resin. (Also see fibre exposure)

weave texture A surface condition of base material in which a weave pattern of glass is apparent although the broken fibres of the woven cloth are completely covered by resin.

webbing Solder adhering to the surface of a solder mask after the soldering operation.

wedge lock Mechanical hardware utilized for constraining the edges of a circuit board assembly in a mechanical chassis. It reduces the possibility of damage due to board vibration and improves the heat conduction path between the assembly and the chassis.

wet solder mask Applied by means of distributing wet epoxy ink through a silk screen, a wet solder mask has a resolution suitable for single-track design, but is not accurate enough for fine-line designs.

wetting In general, wetting is the ability of a liquid to flow across a surface as opposed to sticking to itself. Wetting occurs when the attraction between liquid and surface is greater than the surface energy of the liquid, drawing a molecularly thin layer across itself.

Wetting in soldering applies to molten solder spreading along the base metal/metallisation surfaces to produce a relatively uniform, smooth, unbroken and adherent film of solder. A good intermetallic bond between surfaces is formed. One action of flux is to reduce the surface tension of the solder to enhance wetting.Good wetting is indicated by a low ‘contact angle’ (positive wetting angle) between the solder fillet and the base metal/metallisation.

whisker A slender needle-shaped growth between conductors and lands which occurs after the printed board has been manufactured.

wicking Absorption of liquid by capillary action along the fibres of the base metal. For an alternative use, see solder wicking.

wire Besides its usual definition of a strand of conductor, wire on a printed board also means a route or track.

wire pullout force The force at which a cable will fracture or pull out of the termination at the back of a contact in a connector. The pull out force must be no less than the breaking strain of the plain wire.

wire wrap area A portion of a board riddled with plated-through holes on a 100-mil grid. Its purpose is for accepting circuit changes which may be found necessary after a board has been manufactured, stuffed, tested and debugged.

wiring harness A prefabricated bundle of wires.

workmanship requirements A set of quality standards that must be met by a manufactured PCA.

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