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Glossary of terms

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Term Definition
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.
Td   (glass decomposition temperature) The temperature at which material weight changes by 5%. This parameter determines the thermal survivability of the resin material.
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 coefficient   (TC) The ratio of a quantity change of an electrical parameter, such as resistance or capacitance, of an electronic component to the original value when temperature changes, expressed in %/ºC or ppm/ºC.
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.
tenting   The covering of holes in a printed board and the surrounding conductive pattern with a dry film resist.
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 board   A printed board that is deemed to be suitable for determining the acceptability of a group of boards that were. Or will be, produced with the same fabrication process.
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 fixture   A device that interfaces between test equipment and the unit under test.
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   (glass transition temperature). The point at which rising temperatures cause resin inside the solid base laminate to start to exhibit soft, plastic-like symptoms. This is expressed in degrees Celsius (°C).
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
thick film hybrid   An alternative to a printed circuit board (PCB), it is generally smaller, more secure and more robust than a PCB.  Thick film hybrid microcircuit technology involves the precision screen printing and firing of conductors, resistors and dielectrics onto a ceramic, titanium or stainless steel substrate for multilayer circuitry.
thief   An extra cathode placed as to divert to itself some of the current from portions of the board which otherwise would receive too high a current density.
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.
thou   (somewhat old-fashioned) UK name for one thousandth of an inch, equal to 25.4µm.
through connection   See feed-through.
through-hole   (also spelt ‘thru-hole’). 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. Also describes 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   Segment of a conductor route or net.
track   Trace.
transmission line   A conductor that is configured to have a specific impedance value. See microstripline and stripline.
true position   The theoretically exact location of a feature or hole established by a basic dimension.
true positioning tolerancing   See geometric dimensioning.
TS16949   The ISO/TS16949 is an ISO technical specification aiming to the development of a quality management system that provides for continual improvement, emphasizing defect prevention and the reduction of variation and waste in the supply chain. It is based on the ISO 9001 and the first edition was published in March 2002 as ISO/TS 16949:2002. It was prepared by the International Automotive Task Force (IATF) and the "Technical Committee" of ISO. It harmonizes the country-specific regulations of Quality-Management-Systems. About 30 percent of the more than 100 existing automobile manufacturers affiliate the requirements of the norm but especially the large Asian manufacturers have differentiated, own requirements for the quality management systems of their corporate group and their suppliers. TS16949 applies to the design/development, production and, when relevant, installation and servicing of automotive-related products. It is based on ISO 9001. The requirements are intended to be applied throughout the supply chain. For the first time vehicle assembly plants will be encouraged to seek ISO/TS16949 certification.
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
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.
turnkey   A type of outsourcing method that turns over to the subcontractor all aspects of manufacturing including material acquisition, assembly and testing. Its opposite is consignment, where the outsourcing company provides all materials required for the products and the subcontractor provides only assembly equipment and labor.
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   A printed circuit assembly (PCA) with surface mount technology (SMT) devices on the top side, bottom side or both sides of a board.
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 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.