Vapour Phase

The solder re-flow process that uses a vaporized solvent as the source for heating the solder beyond its melting point,creating the component-to-board solder joint.

Vacuum Pick-up

A component handling tool with a small vacuum cup for ease of pick-up and removal during de-soldering.

Unsupported Hold

A hole containing no conductive material nor any other type of reinforcement.

Underwriters’ Symbol

A logotype authorized for placement on a product which has been recognized (accepted) by Underwriters Laboratories, Inc. (UL).

Undercut

A groove or excavation at one edge of a conductor caused by etching.

Ultrasonic Soldering

Fluxless soldering wherein molten solder is vibrated at ultrasonic frequencies while making the joint.

UL

Underwriter’s Laboratories, Inc., a corporation for the purpose of establishing safety standards on types of equipment or components in USA and Canada.

Twist

The deformation of a rectangular sheet, panel or printed board, that occurs parallel to a diagonal across its surface in such a way that one of the comers of the sheet is not in the plane formed by the other three corners.

Trim Lines

Lines which define the borders of a printed board.

Triazine

Dielectric material with higher glass transition temperature and better thermal stability than epoxy resin, however, more expensive and not in common use.

Transmission Line

A signal-carrying circuit composed of conductors and dielectric material with controlled electrical characteristics used for the transmission of high-frequency or narrow-pulse type signals.

Transmission Cable

Two or more transmission lines.

Traces

The metallic conductive strips that provide connections between components, terminals, etc., on printed circuits.

Trace

A single conductive path in a conductive pattern.

Tombstoning

A soldering defect in which a chip component moves into a vertical position during solidification of the solder so that only one terminal is connected. It is caused by defective re-flow processing.

Tolling Hole

Also called fabrication hole, pilot hole, or manufacturing hole. These are used as PCB reference points upon which other dimensions are based.

Tinning

The application of molten solder to a basis metal in order to increase its solderability.

Through Connection

An electrical connection between conductive patterns on opposite sides of an insulating base, e.g. plated through-hole or clinched jumber wire.

Thermoset

A plastic cured or hardened by heating into a permanent shape. Thermosets cannot be re-melted.

Thermoplastic

A plastic set into final shape by forcing the melted polymer into a cooled mould. The hardened form can be re-melted several times.

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