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.

Thermocouple

A device made of two dissimilar metals which, when heated, generate a voltage that is used to measure temperatures.

Test Point

Special points of access to an electrical circuit, used for testing purposes.

Test Pattern

A pattern used for inspection or testing purposes.

Test Fixture

A device that adapts a specific assembly under test system via inter-connection.

Test Coupon

A pattern as an integral part of the PCB on which electrical tests may be made to non-destructively evaluate process control. A portion of a circuit used exclusively to functionally test the circuit as a whole.

Test Board

A printed board suitable for determining acceptability of the board or of a batch of boards produced with the same process so as to be representative of the production board.

Terpenes

(Turpentine)A solvent used in cleaning electrical assemblies.

Termination

 The part of component that makes contact with a pad on a substrate.

Terminal Area

A portion of a conductive pattern usually, but not exclusively, used for the connection and/or attachment of components.

Tenting

A printed board fabrication method of covering over plated through-holes and the surrounding conductive pattern with a resist, usually dry film.

Tented Via

A via with solder mask completely covering both its pad and its plated through-hole. This completely insulates the via from foreign objects, thus protecting against accidental shorts, but it also renders the via unusable as a test point.

Temperature Profile

 The depiction of the temperature that a selected point traverses as it passes through the re-flow process.

Teflon

Du Pont trade name as an inventor for PTFE(Polytetrafluoroethylene).

Taped Components

Components attached to continuous tape for automatic assembly.

Tape-and-reel

A packaging method of housing surface-mount parts in  their own tape cavities in a long continuous strip. The cavities are covered so that the tape can be wound around a reel for convenient handling and machine set-up.