radial lead A lead extending out of the side of a component rather than from the end. The opposite lead configuration is the axial lead.

radiant heat transfer The electromagnetic radiation emitted by one body due to the temperature difference between it and another body, the radiation being proportional to the difference.

radiation, focused infrared Infrared concentrated on a point or line by a backup reflector.

radiation, infrared Thermal radiation emitted in the infrared wavelength region (0.7–1000 microns) of the electromagnetic spectrum.

radiation, long wave IR Infrared occurring between the wavelengths of 5–100 microns.

radiation, medium wave IR Infrared occurring between the wavelengths of 2.5–5 microns.

radiation, near IR Infrared occurring between the wavelengths of 0.78–2.5 microns. Also called short wave IR radiation.

radiation, non-focused infrared Infrared scattered over an area by a diffuse backup reflector.

radiation, re-emitted infrared Thermal energy absorbed by a media that is re-emitted as infrared at a wavelength dependent on its temperature.

radiation, reflected infrared IR energy that is redirected to a target. No change in wavelength occurs.

radiation, short wave IR Infrared occurring between the wavelengths of 0.78–2.5 microns. Also called near IR radiation.

radiation, thermal infrared Thermal electromagnetic radiation heat transfer occurring between the wavelengths of 0.78–1000 microns.

random access memory (RAM) A type of memory that offers access to storage locations within it by means of X and Y coordinates.

read only memory (ROM) A random access storage in which the data pattern is unchangeable after manufacture.

real estate The surface area of an integrated circuit or of a substrate. The surface area required for a component or element.

reduction Removal of oxygen from a compound. Reduction typically signifies a decrease in an element’s or an ion’s positive charge.

reference designators Diagram markings that distinguish one graphic symbol from another and correlate these identifications with actual components on the parts lists and assembly drawings. They consist of a combination of letters and numbers that identify the class of the component.

reflectivity Percentage of incident infrared that reflects from the surface, thus having no heating effect.

reflow of through-hole Process in which through-hole components populating a PCB assembly are reflow soldered simultaneously with surface mount components (rather than wave soldered or hand soldered). Also known as single center reflow soldering, paste-in-pin, pin-in-paste, and intrusive soldering.

reflow process A general term referring to the overall process of reflowing solder paste in attaching surface mount components to various substrates. It usually includes the preheat process, stabilization and/or drying, the reflow spike, and cooldown, but sometimes refers to the reflow spike area only. Also called reflow soldering.

reflow soldering A process for joining parts to a substrate by depositing solder paste, placing parts, heating until the solder fuses, and allowing them to cool in the joined position. Also referred to as the reflow process.

reflow spike A portion of the reflow process where the temperature is raised sufficiently to cause the solder paste to reflow.

registration The location of a circuit with respect to fixed points. Successive operations must register properly so opposite sides of the circuit will mate properly, holes will fall in center of pads, and tabs will fit into connectors.

repair The act of restoring the functional capability of a defective part without necessarily restoring appearance, interchangeability, and uniformity.

repeatability The ability to repeatedly return to a specific target. Used when evaluating the consistency of processes and process equipment.

resin A solid or semi-solid organic compound lacing a crystalline structure. Resins are characterized by not having definite and sharp melting points, are usually not conductors of electricity, and many are transparent or translucent. Natural resins usually originate in plants, such as pine sap, and are not water soluble. The rosin used in soldering fluxes is an example of resin.

resin recession A void between the plated through-hole barrel and the wall of the holes when viewed in cross section after exposure to high temperatures.

resin smear A condition usually caused by drilling in which the resin is transferred from the base material to the wall of a drilled hole covering the exposed edge of the conductive pattern.

resist A material used to mask some process action from a given part of an assembly. An example is a resist used in soldering to cover those parts of the bare conductor over which a solder coat is not desired.

resistance A measure of the difficulty of moving an electrical current through a material when a voltage is applied.

resistance heating A method of heating that depends on one of two principles: (1) The passage of large currents through a poor conductor like graphite or resistive alloys. Here the heat generated in the tool is transferred by conduction to the work—common in soldering. (2) The resistance of an air gap that causes an arc and rapid heating until the gap is filled by molten metal—common in brazing and welding.

resolution (1) PCB Fab: The ability to reproduce artwork of various size lines and spaces. (2) PNP (Pick and Place): Defines the finest increments of machine movement, and hence, the ultimate precision of the equipment. (3) Vision: The number of pixels per screen image. The larger the number, the better the resolution.

response time The time required for thermal equilibrium to occur after a setpoint change is made on a reflow machine.

rework The act of repeating one or more manufacturing operations for the purpose of bringing a non-conforming item into conformance with a drawing, specification, or contract requirement.

rheology (1) A term used to describe the flow of a fluid. Typically used to describe the viscosity and surface tension properties of a solder paste. (2) Describes the flow of a liquid, as with solder paste or epoxy, or its viscosity and surface tension properties.

robber An area designed around a printed circuit board to absorb unevenly distributed current.

rosin A naturally occurring resin usually associated as a component of pine sap. It is a mixture of several organic acids, of which abietic acid is the chief component. Available as gum, wood, and Tall Oil Rosins, sometimes chemically modified. The most widely used material in the manufacture of soldering fluxes for the electronic industry is water white (ww) gum rosin.

rosin flux The mildest and least effective of solder fluxes. To increase rosin flux efficiency, small amounts of organic activating agents are added. Type RMA, mildly activated rosin flux, is the flux most commonly used for electrical connections.

rotational error The angular displacement of the component axes resulting from component centering-mechanism inaccuracies and placement tool rotational precision.

router (CAD) A computer program that determines paths between interconnecting points.