TAB = Tape Automated Bonding A process for interconnecting an integrated circuit die to the substrate surface using a fine lead frame supported by a carrier film (usually Kapton tape). The TAB process starts by bonding the IC die to the patterned inner leads on the tape, generally followed by testing. In a separate operation, the outer leads are positioned over the substrate pads and bonded to them. Most interconnection uses solder processes, but welding and conductive adhesive attachment are also found.

Tape-and-reel Method of housing parts in separate cavities in a long continuous strip. The cavities are covered with a plastic sheet to facilitate winding the strip around a reel for component presentation or ‘feeding’ to automated placement equipment.

TCE See CTE.

TCOW: True Cost of Waste. The cost of waste is always much greater than just the cost of disposal, and can be as much as 5–10% of a company’s turnover. Waste disposal is the obvious ‘visible’ cost but there are numerous hidden costs.

TDR = Time Domain Reflectrometry. TDR is a technique which is used for measuring the characteristic impedance of a printed circuit trace. The equipment measures the way in which a pulse is reflected from discontinuities in the transmission line created by the trace.

temperature gradient The rate of change in temperature, which can be expressed in terms of change per unit of distance or per unit of time.

tensile strength Ability of a solder joint to resist a force applied perpendicular (upward) from it.

tented via a via with dry film solder mask completely covering both its pad and its plated-thru 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. Sometimes vias are tented on the top side of the board and left uncovered on the bottom side to permit probing from that side only with a test fixture.

terminal A point of connection for two or more conductors in an electrical circuit; one of the conductors is usually an electrical contact or lead of a component.

terminal area See land.

terminal hole A hole used for attachment and electrical connection of component terminations, including pins and wires, to the printed board. (Also referred to as ‘component hole’)

terminal pad See land.

termination An electric input or output point of a circuit or component to which electrical connections can be made.

terminator A device (usually resistive) attached to the end(s) of a transmission line to prevent or reduce signal reflections that could affect the performance of the circuit.

ternary alloy Alloy consisting of three metals (e.g. tin/lead/silver).

test coupon A portion of a printed circuit board or panel, dedicated for test purposes, that undergoes the same fabrication processes as the board, and can therefore be used to determine its acceptability. Typically test coupons are standard patterns which enable the fabricator to compare different products.

Some test coupons are subjected only to non-destructive electrical tests to evaluate the fabrication process; in other cases the test coupon can be separated from the board and then used for destructive testing. Test coupons are used not only to verify quality and conformance of individual batches, but also to monitor the long-term quality of the board and fabrication process.

test pad Designated points of access to a circuit or component for testing purposes.

test pattern During testing of a PCA, patterns of signal faults are inserted into the circuitry, and its response is observed to determine if the faults were recognized appropriately. See circuit fault.

test point Special points of access (a terminal or plug-in connector) provided in a circuit, used for electrical testing purposes or to facilitate monitoring, calibration, or trouble-shooting.

Tg see glass transition temperature.

theory of operation A description of how a circuit design is supposed to function.

Thermal Coefficient of Expansion (TCE) see CTE (Coefficient of Thermal Expansion)

thermal grease A viscous material (such as silicone grease) that is inserted between two surfaces to enhance heat transfer between them.

thermal relief pad A land configuration used for connecting plated through-holes to large conductive areas (power or ground planes) which become heat sinks during a soldering operation. It prevents excessive loss of heat of the solder in the hole, which could result in formation of an inadequate joint.

thermode A heated bar that is used during rework/repair of a PCA to remove a component by simultaneously desoldering multiple component leads

thieves (plating thieves) Non-functional metal areas on a surface to be electroplated. Their purpose is to balance the current density during plating to ensure uniform build-up of plated material. See dummy traces.

thin film hybrid See hybrid circuit.

thixotropy ‘Memory’ property of a fluid (especially of solder paste) whereby its viscosity (resistance to flow) depends on its recent history of flow and not just on the force applied to it. See also shear thinning.

through connection See feed-through.

through-hole 1) (noun) A hole that extends though the entire circuit board, which may or may not be plated, depending on its function. Plated through-holes are used for the attachment and electrical connection to the printed board of component terminations, including pins and wires. 2) (adjective) (also spelt ‘thru-hole’). Of a component, having pins designed to be inserted into holes and soldered to pads on a printed board. Contrast with surface mount.

through-hole technology The science applied to making electrical connection of components to and through the surface of a conductive pattern using component holes (in contrast to SMT).

through-hole via A plated hole made to extend completely through a circuit board hole for the sole purpose of connecting conductors on one or more layers.

tinning The application of a solder coating to a basis metal (e.g. conductive paths and terminals) to enhance solderability and minimise oxidation.

tombstoning A soldering defect condition observed after reflow soldering, in which leadless devices such as chip resistors or capacitors stand on their end, with only one edge soldered to lands on the circuit board, resembling a tombstone. Also referred to as the Stonehenge or Manhattan effect. Tombstoning is caused by force imbalances during solder reflow, with a variety of root causes. See also ‘ drawbridging’.

tooling hole A hole in a circuit board or fabrication panel that is used for positioning purposes; for example, at fabrication, to align the panel with the artwork; at assembly, to facilitate handling, and as a means of rough alignment for component placement. Typically tooling holes are treated in such a way as to be very accurate at the fabrication stage, whereas assembly processes normally rely for accuracy on the position of copper features.

top or bottom entry sockets refer to the direction from which the connectors plug together (that is, bottom entry means that the plug connector has to pass through holes or slots in the PC board).

top side The primary side of a PCA, usually containing the most complex or major components. The top side of a PCA having some or all through-hole components (Assembly Types II and III) is the side with the through-hole component bodies, and is also referred to as the ‘component side’. The top side of a PCA having all SMT components (Assembly Type I) is the final side to receive component mounting materials and components. See Types I/II/II assemblies.

TQFP Thin Quad Flat Pack. Essentially the same as a QFP except low-profile, that is, thinner.

trace(track) Segment of a route. See conductor.

transmission line A conductor that is configured to have a specific impedance value. See microstripline and stripline.

treatment: Involves the physical, chemical or biological processing of waste to reduce their volume or harmfulness.

true position The theoretically exact location of a feature or hole established by a basic dimension.

true positioning tolerancing See geometric dimensioning.

TSOP = Thin Small Outline Package As with SQFP, this term and the related TSSOP refer to fine pitch low-profile packages. Similar in style to the SOP, but substantially smaller. The term ‘shrink’ refers to the reductions in the footprint of the package; ‘thin’ generally means that both lead frame and package have been designed to allow a much thinner resin coat than the standard SOP

TSSOP = Thin Shrink Small Outline Package See TSOP.

tube feeder A parts packaging method in which parts are inserted end-to-end in an anti-static plastic tube or stick. Indexing for feeding to the placement tool may be accomplished by vibration or spring action.

twist The deformation parallel to a diagonal of a rectangular sheet such that one of the corners is not in the plane containing the other three corners.

two-part connector A device that provides a mechanically pluggable interface for electrical terminations. One half of a connector pair is mounted on a circuit board and the mating half is electrically connected to the rest of the system.

Type I, II, III assembly Designating PCB assemblies (I) SMDs mounted on one or both sides of the board; (II) mixed technology having leaded (through-hole) parts mounted on the primary side and SMDs on one or both sides; and (III) mixed technology featuring passive SMDs on the secondary side and leaded components mounted to the primary side.

• Type I A printed circuit assembly (PCA) with surface mount technology (SMT) devices on the top side, bottom side or both sides of a board.
• Type II A printed circuit assembly (PCA) with a mixture of surface mount and through-hole components placed only on opposite sides of the board.
• Type III A printed circuit assembly (PCA) with a mixture of surface mount and through-hole components, where the SMT components are placed on both sides of the board and the through-hole components are placed only on the topside of the board.

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