SAE = Society of Automotive Engineers A US technical society that prepares and publishes material and process specifications, standards, technical papers, and books.

saponifier An aqueous solution of organic or inorganic base and additives for dispersing and removing rosin and water-soluble flux residues via chemical reaction as a detergent solution.

scavenging See leaching.

schematic (diagram) A diagram, drawing or plan which shows, by means of graphic symbols, the parts, electrical connections and functions of a specific circuit arrangement.

schematic symbology A graphic diagram used to represent a specific type of component and its terminations on a schematic diagram.

scorch To burn an exposed surface so as to change its colour or texture.

screening 1) A process for transferring an image to a surface by forcing a viscous liquid material (such as ink, resist, or solder paste) through a screen with a squeegee. 2) The process of inspecting or testing a group of materials or parts to weed out noncompliant items.

screen print The decals and reference designators in epoxy ink on a printed circuit board, so called because of their method of application: see legend.

secondary side The side of the assembly that is commonly referred to as the ‘solder side’ in through-hole technology. In SMT, the secondary side may be either reflow-soldered or wave-soldered.

selective plating (sometimes called duplex plating) Connector contacts can be electroplated all over, usually with tin or gold. More common today are selective plating processes whereby gold is plated onto the mating contact area for optimum electrical performance and tin is plated onto the tail for solderability performance.

self-alignment The tendency of components slightly misaligned during placement to self-align with respect to their land pattern during reflow soldering, due to the surface tension of molten solder. Minor self-alignment is possible but one should not count on it!

semi-aqueous cleaning This cleaning technique involves a solvent cleaning step, hot water rinses and a drying cycle.

semiconductor A solid crystalline substance whose electrical conductivity falls between that of a conductor and an insulator.

semiconductor device An electronic component containing an active circuit material whose conductivity can be varied by a variety of external inputs (voltage, light energy, heat, etc.).

sequencing interconnections Controlling the order of interconnection of nodes in a net during routing to enhance the performance of sensitive circuits.

shadowing A condition in which solder fails to wet the device leads during the wave-soldering process. Generally the trailing terminations of a component are affected, because the component body blocks the proper flow of solder. Requires proper component orientation to correct the problem.

shear strength Ability of a solder joint to resist a force applied parallel to the printed circuit board.

shear thinning The property of a fluid (usually solder paste) whereby the viscosity (that is, the resistance to flow) reduces temporarily as the fluid is subjected to an increased shear force, (for example by a squeegee during the print process.

shielding An electrically conductive physical barrier designed to reduce the detrimental interaction of electromagnetic fields upon devices or circuits. Commonly attached to cables or connector housings to protect against EMI and mechanical damage. See EMI/EMC.

short (short circuit) An abnormal connection of relatively low resistance between two points of a circuit. The result is excessive (often damaging) current between these points. At the design phase, such a connection is considered to have occurred in a CAD database or artwork whenever conductors from different nets either touch or come closer than the minimum spacing allowed for the design rules being used.

shrouded contacts Contained within the outline of the moulding, so preventing contact damage. Un-shrouded contacts protrude beyond the outline of the moulding.

signal 1) A net. 2) A net other than a power or ground net.

signal coupling See circuit coupling.

signal edge The forward or trailing part of a signal pulse that causes a gate to change logic states.

signal flow The movement of data through a circuit.

signal integrity The specified purity (lack of distortion) of a signal transmitted through a circuit required for proper operation. Design of a circuit, selection of electronic parts, their physical placement on a board, and the location and physical configuration of the interconnections all have a significant effect on signal integrity, especially for high speed circuitry.

signal layer An interconnection layer on a circuit board devoted exclusively to the routing of signal traces.

signal propagation delay The time it takes a signal to travel (propagate) in a line, compared to its theoretically possible speed. This is mainly a function of the characteristic impedance of the line, the dielectric constant of the surrounding material, and the type and number of the components attached to the line.

signal rise and fall times The time it takes the edge of a signal pulse to reach a value that will cause a gate to change states.

signal timing The speed at which a signal that causes digital devices to switch (change states), travels in a circuit. See clock speed.

silicon A non-metallic element used in the semiconductor industry as a substrate for multiple layers of material, built to form transistors and integrated circuits. Silicon is grown from a crystal to form a cylinder shaped ‘log.’ Slicing the logs into sections 1/40 of an inch thick creates bare wafers.

silicon wafer A thin, iridescent, silvery disk of silicon which contains a set of integrated circuits, prior to their being cut free and packaged.

silkscreen 1) The decals and reference designators in epoxy ink on a printed circuit board, so called because of their method of application: see legend. 2) A data file controlling the photoplotting of this legend.

SIMM = Single In-line Memory Module A high-density DRAM package alternative consisting of several plastic leaded chip carriers (PLCC) connected to a single printed circuit board (PC board). SIMMs provide an upgrade vehicle for future generations of DRAMs without having to redesign the PC board.

simulation Use of a computer program that duplicates the characteristics of an entity. Its purpose is to verify the performance of a design before committing it to a hardware implementation. See modelling.

single track PCB design with only one route between adjacent DIP pins.

single-sided (single-layer) board A PCB with metallised conductors on one external surface only. Any through holes are unplated.

SIP = Single-In-Line Package A component package that has a single row of terminals, pins, or lead wires along one edge of the package.

SIR = Surface Insulation Resistance A measure of the electrical resistance of the surface of an insulator. Its units are ohms, but normally quoted as ‘ohms per square’, reflecting the fact that the resistance value measured between conductors will depend linearly on their separation and inversely on their width. SIR test means a test for the maintenance of a high SIR valu under conditions of applied voltage, temperature and humidity, which is used to assess the suitability of flux materials and cleaning processes. Ionic residues lead to rapidly deteriorating values of SIR.

skew Describing the misalignment of a component or device to its proper mounting site.

skipping (solder skip) Condition found in wave soldering, when adjacent conductor areas are not all coated with solder.

slump A spreading of material (solder paste, adhesive, thick film, etc.) after stencil printing but before curing. An excessive slump detracts from definition. If loss of definition is the result after reflow, it is cause for rework.

SMD (SMC) = Surface Mount Device (Component) An electronic device designed for mounting onto lands on the surface of a substrate rather than by insertion into holes in the substrate. SMD is a registered service mark of North American Philips Corp. (Assembléon) to denote resistors, capacitors, SOICs and SOTs.

SMOBC = solder mask over bare copper The application of solder mask material over unplated copper conductors. There is sometimes a concern that solder plating on conductors that are covered by mask material will remelt and flow during the board soldering operation, damaging the mask and the board itself. SMOBC eliminates that possibility.

SMT = Surface Mount Technology A method of assembling printed wiring boards or hybrid circuits, where components are attached to pads on the board surface, as distinct from through-hole technology, where component leads are inserted into holes. The result is higher component density, and smaller assemblies.

Sn Chemical symbol for tin.

snapback The return of a stencil to normal (flat plane) after its deflection by a squeegee across its surface.

soak That part of the solder reflow process in which internal temperature differences between components are permitted to equalize (stabilization).

soft Pertaining to or consisting of software.

software Programs, data files, procedures, rules, and any associated documentation pertaining to the operation of a computer system or of a computer application.

SOIC = Small-Outline Integrated Circuit A plastic-encapsulated surface-mounted IC package with parallel rows of leads on the two longer sides. The leads are formed into a gull-wing shape, with standard spacings between leads and rows. The original SOIC had leads on 1.27mm (0.05 in) spacing, and this is still commonly found; more recent package formats have narrower lead spacings See also SOJ.

SOJ = Small Outline J-Leaded A surface-mounted IC package with two parallel rows of J-leads, with standard spacing between leads and rows. Generally used for memory devices, where the rows of leads are typically on the narrow edges. Most of these parts use finer pitches than standard SOICs, and are also substantially thinner.

solder A fusible alloy used to join two or more metals at temperatures below their individual melting points. Solders which melt readily are ‘soft solders’, others fusing at a higher temperature (usually taken as above 425°C) are ‘hard solders’. Solders consisting mostly of tin and lead are normally used for soldering electronic assemblies. The tin in solder forms an intermetallic with copper (or nickel) in the surface being bonded.

solder balls Small spheres of solder which have separated from the main body of the solder joint and adhere to laminate, mask, or conductors. Most often associated with the use of solder paste containing excessive oxides or moisture. Baking of paste may minimise formation of solder balls, but over-baking may cause excessive balling.

solder braid Flat strips of copper braid used to soak up liquid solder from pads and components. Solder braid comes in a variety of thicknesses and is usually impregnated with flux to aid the wetting of the solder to the copper braid. Also called solder wick.

solder bridging See bridging.

solder bumps The spherical solder materials bonded to a passive or active device contact area that serve as connections to circuit pads.

solder contact angle See contact angle.

solder dam A neck-down (narrowing) of a conductor that restricts the flow of molten solder. Its main purpose is to ensure that the proper amount of material remains at the solder joint that is being formed.

solder fillet (see fillet)

solder impurities Trace metals (other than tin and lead) and contaminants which exist in the solder. With age and continued usage, impurities become more prevalent in solder baths or pots and in wave soldering machines.

solder joint contamination The presence of foreign matter in a solder connection.

solder levelling or fusing The process of remelting plated solder (tin-lead) on the surface of a circuit board to control its thickness, reduce granularity, and eliminate harmful oxidation.

solder mask A coating material used to mask or protect selected areas of a pattern from the application of solder. Usually applied to a PCB to allow solder to adhere only to the pads and other unmasked areas. Also referred to as ‘solder resist’.

solder paste (cream) A homogeneous combination of minute spherical solder particles, flux, solvent, and a gelling or suspension agent, which has the consistency and viscosity of a paste and is used in surface mount reflow soldering. Solder paste can be deposited on a substrate by solder dispensing and screen or stencil printing.

solder preforms Special solder forms or configurations, frequently supplied as stamped washers, spheres or formed wire, that generally contain a predetermined alloy and a flux core or coating.

solder projection An undesirable solder protrusion from a solidified joint or coating. Dependent on its shape, also referred to as ‘icicle’, ‘solder horn’ or ‘peak’.

solder side In assembly of plated through-hole components, the term refers to the soldered side of the PCB. With SMT, it means the secondary side generally is limited to passive chip parts.

solder splashes Drops of solder in areas that should be free of solder; an undesirable condition that could cause electrical shorts.

solder voids The absence of solder on the joint surfaces or pockets of bare spaces resulting from failure of the alloy to completely wet the joint.

solder wicking Capillary action, caused by surface tension, leads solder to fill small spaces such as holes, between strands of wire up a pad or component lead, or under the insulation of a covered wire. The effect worsens if there are temperature differentials, because the surface tension of solder increases with temperature, causing it to travel towards a heat source.

Wicking is a redistribution of solder away from the intended joint caused by surface tension. With leaded packages, excessive wicking can lead to there being insufficient solder at the lead-to-pad interface. Solder wicking is frequently caused by rapid heating during reflow or excessive lead non-coplanarity

solderability The ability of a metal surface. such as a lead, pad or trace. to be wetted by molten solder to form a strong bond.

soldering Process by which two or more metal surfaces are bonded together via an intermediary alloy called a solder.

solids content The weight percentage of rosin (solids) in a flux formula.

solidus The temperature at which some components of the solder alloy begin to melt. See liquidus and pasty range.

solvent Any solution capable of dissolving a solute. In the electronics industry, aqueous, semi-aqueous and non-ozone-depleting solvents are used. As used when referring to fluxes, the ‘solvent’ is the liquid carrier for the flux ingredients, which allows even distribution of the flux material. During the pre-heating of the board the solvent is intended to evaporate, so that little, if any, is present when the board contacts the solder wave. For most fluxes, the solvent is isopropanol and/or some other alcohol.

solvent cleaning The removal of organic and inorganic soils using a blend of polar and non-polar organic solvents.

SOT = Small Outline Transistor A plastic surface-mounted package, for use with a transistor or diode, that has two gull wing leads on one side of the package and one on the other.

special waste: Defined by the Environmental Protection (Special Waste) Regulations 1996 (as amended) and is broadly any waste on the European Hazardous Waste List that has one or more of fourteen defined hazardous properties.

SPICE A computer tool that is used to analyse the performance of analogue circuitry.

SQFP = Shrink Quad Flat Pack See QFP. As with the SOP, the QFP has been developed to take up less valuable board area. ‘Shrink’ is the term associated with reducing the plan dimensions of the package, and is always accompanied by a reduction in lead pitch, and usually by an overall thinning of the package.

spring contacts in a connector can have one, two, three, four or six cantilever or beam contacts. These are usually called single beam, twin leaf or twin beam, three, four or six leaf or finger contacts. Two-part contacts comprise a precision turned outer shell with an integral stamped and formed inner spring contact.

squeegee A rubber or metal blade used in stencil printing to wipe solder paste across the stencil face, forcing the material through the patterned apertures and onto the PCB.

SRAM = Static Random Access Memory An integrated circuit similar to a DRAM which requires no constant refreshing or recharging. It retains stored information as long as power is applied to the computer, hastening information retrieval process time.

stack-ability Where a connector has its length and/or breadth narrow enough to allow two connectors to be placed together, and maintain contact pitch centres. This can be side-to-side (side stackable) or end-to-end (end stackable).

stack-up Defines the construction and lay-up of a circuit board.

stamped and formed contacts are made from originally flat strip (usually non-ferrous materials) and are stamped out of the strip and formed up into spring contacts.

stand-offs Moulded pips or bars that allow cleaning fluids to pass between the connector housing and the top face of the PCB, if is necessary after the soldering operation to remove flux residues, etc.

static and dynamic thermal conditions Heat flow conditions/values that remain constant are considered thermally static. Heat flow conditions that are continuously changing are thermally dynamic.

stencil A metal sheet bearing a circuit pattern cut into the material. Common materials are stainless steel and brass.

strain relief An area between a body and termination which has been formed or treated in such a way as to reduce the forces acting on the body when external forces are applied to induce separation, compaction, or sliding.

stripline A type of high-frequency transmission line configuration that has a specific, characteristic impedance value. It consists of a conductor placed in a precise relationship between two parallel ground planes and surrounded by a dielectric material.

stub A short projection or branch from the main path of a conductor. In high-frequency operation a stub can act as a discontinuity in a circuit, causing degradation of performance.

stuff As in ‘board-stuffing’ a somewhat disparaging term which describes the activity of attaching and soldering components to make a printed circuit assembly.

subassemblies Two or more individually replaceable items integrated to form a system.

sub-panel A group of printed circuits (called modules) arrayed in a panel and handled by both the board house and the assembly house as though it were a single printed circuit board. The sub-panel is usually prepared at the board house by routing most of the material separating individual modules, leaving small tabs. The tabs are strong enough so that the sub-panel can be assembled as a unit, and weak enough so that final separation of assembled modules is easily done.

substrate The base material which forms both the support structure of an electronic circuit and the insulating layer upon which the conductor pattern is fabricated. Provided that the material meets the manufacturing and usage design requirements, the term may refer equally to an epoxy-glass PCB laminate, a flex material, or the ceramic base for a hybrid circuit.

surface mount (technology) See SMT.

surfactant A chemical added to water to lower its surface tension to improve wetting for cleaning. Surfactants are used in fluxes to reduce surface tension at the metal/solder interface to further promote solder wetting, especially when the assembly exits the solder wave. Where the flux is to be used in a foam fluxer, surfactants can also serve as foaming agents.

sustainable development: Development which meets the needs of the present without compromising the ability of future generations to meet their own needs.

sustainable waste management: Using material resources efficiently to cut down on the amount of waste produced. And, where waste is generated, dealing with it in a way that actively contributes to the economic, social and environmental goals of sustainable development.

symbol A simplified design representing a part in a schematic circuit diagram.

synthesizer A computer program that allows an engineer to specify the logic operations that a design is expected to perform. The synthesizer extracts the equivalent logic circuit functions from a library and connects them together as specified by the engineer to form a complete circuit.

system integration See integration.