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.

recovery: Involves the recovery of value from waste, through recycling, composting or incineration with energy recovery.

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.

recurring cost The cost that is incurred for each item produced, including material and labour.

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 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.

reflections The undesirable return of signal energy due to a discontinuity in a transmission line in which the signal is travelling.

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 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 soldering, such as flux or oil.

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:

Designation	Abbreviation	Frequencies	Free-space wavelengths
Very Low Frequency	VLF	9 kHz–30 kHz	33 km–10 km
Low Frequency	LF	30 kHz–300 kHz	10 km–1 km
Medium Frequency	MF	300 kHz–3 MHz	1 km–100 m
High Frequency	HF	3 MHz–30 MHz	100 m–10 m
Very High Frequency	VHF	30 MHz–300 MHz	10 m–1 m
Ultra High Frequency	UHF	300 MHz–3 GHz	1 m–100 mm
Super High Frequency	SHF	3 GHz–30 GHz	100 mm–10 mm
Extremely High Frequency	EHF	30 GHz–300 GHz	10 mm–1 mm

The SHF and EHF bands are often referred to as the microwave spectrum.

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 = Rosin Mildly Activated Flux - the most commonly used flux through 1995, but usually requires cleaning with CFC bearing materials so is being phased out.

ROM = Read-Only Memory A device that is used for permanent storage of information. Data can be read many times, and remains when power is removed from the device.

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.

route 1. n. A layout or wiring of a connection. 2. v. The action of creating such a wiring.

rout A machining process for defining the outline of a circuit board which use cutters similar to end mills. See board profiling

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.