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Glossary of terms

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Term Definition
radial lead   A component terminal that protrudes ray-like from the body of a component.
radiation   The mechanism for transfer of heat from a solid surface (such as a component) by electromagnetic transmission.
RAM (random access memory)   A device that stores information, which can be both written and read many times. Any part of the memory can be accessed directly through an address. Data in RAM cells can be erased or changed by being overwritten or by removal of power from the device.
rat’s nest   A graphic display produced by a CAD system that shows all interconnections between circuit nodes on a layout as a set of straight lines (unrouted connections). [The name comes from the pattern of the lines as they crisscross the board, to form a seemingly haphazard and confusing mess similar to a rat’s nest] This display is useful when optimising part placement.
REACH   Registration, Evaluation, Authorisation and Restriction of Chemicals. REACH is the Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals. It entered into force on 1st June 2007. It streamlines and improves the former legislative framework on chemicals of the European Union (EU). The main aims of REACH are to ensure a high level of protection of human health and the environment from the risks that can be posed by chemicals, the promotion of alternative test methods, the free circulation of substances on the internal market and enhancing competitiveness and innovation. REACH makes industry responsible for assessing and managing the risks posed by chemicals and providing appropriate safety information to their users. In parallel, the European Union can take additional measures on highly dangerous substances, where there is a need for complementing action at EU level.
recovery   Involves the recovery of value from waste, through recycling, composting or incineration with energy recovery.
recurring cost   The cost that is incurred for each item produced, including material and labour.
recycling   Involves the reprocessing of wastes, either into the same material (closed-loop) or a different material (open-loop recycling). Commonly applied to non-hazardous wastes such as paper, glass, cardboard, plastics and metals. However, hazardous wastes (such as solvents) can also be recycled by specialist companies, or using in-house equipment.
reduction   Reducing the quantity or the hazard of a waste produced from a process. It usually results in reduced raw material and energy demands – thus also reducing costs.
reference designator (“ref des”)   An alphanumeric identifier assigned to each electronic component in a circuit. By convention this begins with one or two letters followed by a numeric value. The alpha part defines the type of component (R = resistor, C = capacitor, etc.) and the numeric part is a sequential number assigned to the component (R23 is the 23rd resistor used in the circuit). Where space allows, reference designators usually appear as a white or yellow epoxy ink legend on the board. They are placed close to their respective components but not underneath them, so that they are visible on the assembled board. By contrast, on an assembly drawing a reference designator is often placed within the boundaries of a footprint, in order to eliminate ambiguity on a crowded board.
reference dimension   A dimension without a tolerance that is used only for informational purposes that does not govern inspection or other manufacturing operations.
reflections   The undesirable return of signal energy due to a discontinuity in a transmission line in which the signal is travelling.
reflow   The melting of electrodeposited tin/lead followed by solidification. The surface has the appearance and physical characteristics of being hot-dipped.
reflow soldering   A process of joining metallic surfaces (without melting the base metals) through the mass heating of pre-placed solder (usually in the form of paste) to create solder fillets in the metallised areas.
register   A printing term describing the proper positional alignment of artwork, tooling equipment and materials to ensure clear and accurate reproduction: used as ‘in register’ and ‘off register’. In PCB usage, is applied to the alignment of artwork with respect to the unexposed laminate panels, and of internal and external features, primarily between pads and holes on both sides and on internal layers.
registration   Properly register.
reinforcement   Material embedded in the resin of a laminate to provide additional mechanical strength. Typical materials are glass cloth, random glass fibres, paper, and a variety of high-strength plastic fibres.
reliability   The probability that an item will function under a specific set of conditions, for a stated period of time, without failure or unacceptable degradation of performance.
repair   Restoring the functional capability of a defective PCB, component or assembly.
replaceable contacts   Can be replaced whilst in service by releasing them from their moulding and then the refitting of a new contact.
residue   Excess of unwanted substances remaining after chemical processing.
resin   A nonconductive plastic material, such as epoxy, polyester, or phenolic, used to produce printed circuit laminates.
resist   Any material used to define a pattern by preventing the products associated with a manufacturing process from attacking (etching) or adhering (plating) to the surface covered by the resist. Coating material used to mask or protect selected areas of a pattern from the action of an etchant, plating solution, or solder. Coating material used to mask or protect selected areas of a pattern from the action of an etchant, solder or plating.
re-use   Using materials or products again, for the same or a different purpose, without material reprocessing (such as glass milk bottles or returnable plastic crates).
revision number (or letter)   Sequential alphanumeric designators used on documentation and data to identify and control changes. The revision number or letter of a drawing should be advanced (A to B, etc.) any time the drawing is modified, to differentiate it from the previous version. In some companies, letters are used to denote designs not released for production, and numbers to denote modifications to production designs. See documentation/data release and dash number.
rework   Repetition of a manufacturing process to bring an assembly into compatibility with a spec or contract requirement.
RF (Radio Frequency)   Also abbreviated rf, or r.f., RF is a term that refers to alternating current which will generate an electromagnetic field suitable for wireless broadcasting and/or communications.The RF spectrum is divided into several ranges, or bands. With the exception of the lowest-frequency segment, each band represents an order of magnitude increase in frequency:
rheology   A term describing the viscosity and surface tension properties of solder pastes or adhesives.
ribbon cable   A multiple round conductor cable in flat ribbon format, which can be used in mass termination connectors. It is sometimes colour-coded.
rigid-flex   A circuit board combining both rigid and flexible dielectric materials in a single assembly.
ringing   Short-term spikes in a signal. Usually related in digital circuitry to transients generated when a gate changes (switches) logic states.
risk   The probability of the occurrence and potential negative impact of a decision or action on downstream activities.
RLP (registered land pattern)   A specific component pattern geometry defined by the IPC that has been used and accepted as an industry standard for that type of part.
RMA   Return material authorization.
RMA (Rosin Mildly Activated Flux)   The most commonly used flux through 1995, but usually requires cleaning with CFC bearing materials so is being phased out.
RoHS   The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC; commonly referred to as the Restriction of Hazardous Substances Directive or RoHS was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state. This directive restricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment. It is closely linked with the Waste Electrical and Electronic Equipment Directive (WEEE) 2002/96/EC which sets collection, recycling and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic e-waste.
root number   The portion of an assembly or part number that identifies its unique type or function (for PA123456-001, PA123456 is the root number)
rosin flux   The mildest (and least effective) of solder fluxes, generally used in no-clean soldering. A variant, RMA (rosin, mildly activated), is the most widely used material for electrical interconnect.
rosin joints   A soldered joint in which one of the terminations is surrounded by an almost invisible film of insulating rosin, making the connection intermittently or continuously open even though it looks good. The interface has no metallic or electrical continuity which results in a high resistance condition with low strength.
rotational error   In placement, the angular displacement of a component’s axes as a result of centring mechanism inaccuracy.
rout   A machining process for defining the outline of a circuit board which use cutters similar to end mills. See board profiling
route   1. n. A layout or wiring of a connection. 2. v. The action of creating such a wiring.
routing   1) (Pronounced ‘rooting’) from route, establishing paths on a board for circuit interconnections. (Pronounced ‘rowting’) from rout, using a cutter to define the outline of a circuit board, as described under board profiling.
routing channel   The space available to route conductors between existing circuit features (pads, vias, holes, prerouted traces, etc.).
row spacing   The dimension between rows of electrical contacts across the axis of a connector housing.
rule class   A set of predetermined layout rules [spacing, voltage, conductor size(s), current, isolation, etc.] that are associated with a specific type or class of circuitry. For example, there may be a different rule class used on a layout for analogue circuitry than for digital circuitry on the same PCA.