SMT Terminology Demystified for Surface Mount Technology

Master SMT Terminology with our Expert Guide. Perfect for Beginners & Pros. Boost Your Electronics Manufacturing Know-How Now!
SMT Terminology Demystified for Surface Mount Technology

Table of Contents


Accuracy: The difference between the measured result and the target value.

Additive Process: A method for manufacturing PCB conductive wiring by selectively depositing conductive materials such as copper and tin on the board layer.

Adhesion: A force similar to the attraction between molecules.

Aerosol: Liquid or gas particles small enough to be spread through the air.

Angle of attack: The angle between the screen printing scraper surface and the screen printing plane.

Anisotropic adhesive: A conductive substance whose particles only pass through the Z-axis direction by the current.

Annular ring: Conductive material around the drill hole.

Application-specific integrated circuit (ASIC): A circuit designed for a specific purpose customized by customers.

Array: A group of elements, such as solder balls, arranged in rows and columns.

Artwork: The PCB’s conductive wiring diagram is used to generate a photo master plate, which can be made at any scale, but usually at 3:1 or 4:1.

Automated test equipment (ATE): Equipment designed for automated analysis of function or static parameters to evaluate performance levels and used for fault isolation.

Automatic optical inspection (AOI): A camera-based inspection of models or objects on an automatic system.


Ball grid array (BGA): A packaging form of integrated circuits, with input and output points arranged in a grid pattern of solder balls on the component’s bottom surface.

Blind via: A conductive connection between the outer and inner layers of a PCB that does not extend to the other side of the board.

Bond lift-off: A fault that separates the soldering pins from the surface of the solder pad (circuit board substrate).

Bonding agent: A glue used to bond single layers to form multilayer boards.

Bridge: Solder connecting two conductors that should be electrically connected, causing a short circuit.

Buried via: A conductive connection between two or more inner layers of a PCB, which cannot be seen from the outer layer.


CAD/CAM system: A computer-aided design and manufacturing system that uses specialized software tools to design the structure of printed circuit boards and converts this design into an actual product. These systems include large-scale memory for data processing and storage, input devices for design creation, and output devices for converting stored information into graphics and reports.

Capillary action: A natural phenomenon where molten solder flows against gravity on solid surfaces that are very close together.

Chip on board (COB): A hybrid technology that uses chip components adhered face-up and traditionally connected to the circuit board substrate layer by wire bonding.

Circuit tester: A method of testing PCBs in bulk production that includes a bed of needles, component pin footprints, guide probes, internal traces, load boards, bare boards, and component testing.

Cladding: A thin layer of metal foil that is bonded to a layer of board to form the conductive wiring of a PCB.

Coefficient of thermal expansion: The amount of expansion measured in parts per million (ppm) when the surface temperature of a material increases by one degree.

Cold cleaning: An organic dissolution process that removes residues from completed soldering.

Cold solder joint: A solder joint that indicates insufficient wetting, characterized by a grey, porous appearance due to inadequate heating or improper cleaning.

Component density: The number of components on a PCB divided by the board area.

Conductive epoxy: A polymer material that is made conductive by adding metal particles, usually silver, allowing it to conduct electricity.

Conductive ink: A glue-like substance used on thick film materials to create conductive wiring patterns on a PCB.

Conformal coating: A thin, protective coating applied to a PCB that conforms to the assembly shape.

Copper foil: A thin, continuous layer of metal foil that precipitates on the substrate layer of a circuit board as a negative electrolytic material, serving as the conductive element of the PCB. It adheres easily to the insulating layer, receives a printed protective layer, and forms a circuit pattern after etching.

Copper mirror test: A flux corrosiveness test that uses a vacuum-deposited thin film on a glass plate.

Cure: The physical property change of a material through chemical reaction or heat reaction with pressure/no pressure.

Cycle rate: A component placement term used to measure the machine speed from pick-up to board placement, and return, also known as test speed.


Data recorder: A device that measures and collects temperature from a thermocouple attached to a PCB at specific time intervals.

Defect: When a component or circuit deviates from its normal, acceptable characteristics.

Delamination: Separation of layers in a board, including separation between board layers and conductive cover layers.

Desoldering: The process of removing a soldered component for repair or replacement, including methods such as using desoldering braid, vacuum (solder sucker), and hot air.

Dewetting: The process of molten solder first covering and then recoiling, leaving behind irregular residue.

DFM (Design for Manufacturability): Methods to efficiently produce products, taking into consideration time, cost, and available resources.

Dispersant: A chemical added to water to increase its ability to remove particles.

Documentation: Information about assembly, explaining basic design concepts, types and quantities of components and materials, specialized manufacturing instructions, and the latest versions. Three types are used: prototype and low-volume runs, standard production lines and/or production quantities, and those specified by government contracts that specify actual graphics.

Downtime: The timing equipment is not producing products due to maintenance or failure.

Durometer: Measures the hardness of rubber or plastic using a scraper blade.


Environmental test: A single or series of tests designed to determine the overall effect of external factors on the structural, mechanical, and functional integrity of a given component package or assembly.

Eutectic solders: Two or more metal alloys with the lowest melting point that, when heated, directly transition from a solid to a liquid phase without undergoing a plastic stage.


Fabrication: The process of manufacturing an empty PCB before assembly, including individual processes such as lamination, metal addition/subtraction, drilling, plating, routing, and cleaning.

Fiducial: A specialized marking that is integrated into the circuit board layout to aid machine vision in identifying the orientation and position of the layout.

Fillet: A connection formed by solder between a pad and a component pin, creating a concave connection. Also known as a solder joint.

Fine-pitch technology (FPT): Surface-mount device packaging technology in which the center-to-center spacing of the package pins is 0.025″ (0.635mm) or less.

Fixture: A device used to securely hold a PCB in place for processing in manufacturing equipment.

Flip chip: A type of chip with no wire leads that typically contains a circuit unit. It is designed to connect electrically and mechanically to the circuit via a suitable number of solder balls (conductive adhesive) located on its surface.

Full liquidus temperature: The temperature level at which the solder reaches the maximum liquid state, best suited for good wetting.

Functional test: Electrical testing of the entire assembly in a simulated operating environment to verify functionality.


Golden sample: A component or circuit assembly that has been tested and known to meet the technical specifications, used to compare and test other units.


Halides: Compounds containing fluorine, chlorine, bromine, iodine, or astatine. They are part of the catalyst in soldering flux but must be removed due to their corrosive nature.

Hard water: Water that contains calcium carbonate and other ions, which may accumulate on the inner surfaces of clean equipment and cause blockages.

Hardener: A chemical added to a resin to cause it to cure or harden, also known as a curing agent.


In-circuit test: A type of testing that checks the placement and orientation of components one by one.


Just-in-time (JIT): a production strategy that aims to minimize inventory by supplying materials and components directly to the production line just before they are needed.


Lead configuration: Conductors that extend from a component and serve as both mechanical and electrical connection points.

Line certification: Confirmation that the production line is under control and can produce reliable PCBs as required.


Machine vision: One or more cameras used to help locate the center of components or improve the accuracy of component placement in a system.

Mean Time Between Failure (MTBF): The average statistical time interval between failures that may occur in an operating unit, usually calculated in hours, and the result should indicate the actual, expected, or calculated value.


Nonwetting: A condition in which the solder does not wet or adhere to the metal surface. This is typically due to contamination on the surface and is characterized by the visible exposure of the base metal.


Omegameter: An instrument used to measure the level of ion residue on the surface of a PCB. It works by immersing the assembly in a mixture of alcohol and water with a known high resistivity, and then measuring and recording the decrease in resistivity caused by ion residue.

Open: A situation where two electrically connected points (pins and pads) become separated, either due to insufficient solder or poor co-planarity of the connection points.

Organic activated (OA): A type of flux system that uses organic acids as activators. It is water-soluble.


Packaging density: The number of components (active/passive components, connectors, etc.) placed on a PCB, expressed as low, medium, or high.

Photoplotter: Basic equipment used for generating original PCB layout diagrams (usually to scale) on photographic films.

Pick-and-place equipment: A programmable machine with a robotic arm that picks up components from automatic feeders and places them at predetermined locations on a PCB with the correct orientation.

Placement equipment: Machines that combine high-speed and precise positioning to place components on a PCB. They can be categorized into three types: mass transfer for SMD components, X/Y positioning, and in-line transfer systems, which can be combined to accommodate the PCB design.


Reflow soldering: The process of permanently connecting surface-mounted components by placing them into solder paste through various stages, including preheating, stabilization/drying, reflow peak, and cooling.

Repair: The action of restoring the functionality of a defective assembly.

Repeatability: The processing capability of accurately returning to a targeted characteristic. An indicator that evaluates the processing equipment and its consistency.

Rework: The process of bringing improperly assembled components back to compliance with specifications or contractual requirements.

Rheology: The study of the flow of liquids or their viscosity and surface tension characteristics, such as solder paste.


Saponifier: A water-based solution of organic or inorganic components and additives used to facilitate the removal of rosin and water-soluble fluxes through products like a dispersible cleaning agent.

Schematic: A diagram that uses symbols to represent the layout of a circuit, including electrical connections, components, and functionality.

Semi-aqueous cleaning: A technique that involves solvent cleaning, hot water rinsing, and drying cycles.

Shadowing: In infrared reflow soldering, the phenomenon where the body of a component blocks energy from certain areas, resulting in the insufficient temperature to fully melt the solder paste.

Silver chromate test: A qualitative check for the presence of halide ions in RMA flux.

Slump: The spreading of materials such as solder paste or adhesive before curing after stencil printing.

Solder bump: A ball-shaped solder material attached to the contact area of passive or active components to establish a connection with the circuit pad.

Solderability: The ability of a conductor (pin, pad, or trace) to wet (become solderable) to form a strong connection.

Soldermask: A process technology for printed circuit boards where all surfaces, except for the points of connection to be soldered, are covered by a plastic coating.

Solids: The weight percentage of rosin in the flux formula (solid content).

Solidus: The temperature at which some solder alloys of components start to melt (liquefy).

Statistical process control (SPC): The use of statistical techniques to analyze process outputs and use the results to guide action to adjust and/or maintain quality control status.

Storage life: The time period for storing and maintaining the usefulness of adhesives.

Subtractive process: The process of obtaining circuit wiring by removing selected portions of conductive metal foils or overlay.

Surfactant: A chemical added to water to reduce surface tension and improve wetting.

Syringe: A container for adhesives that dispenses them through a narrow opening.


Tape-and-reel: A packaging for surface-mount components, in which the components are placed into pockets on a continuous tape, which is then wound onto a reel for use in a pick-and-place machine.

Thermocouple: A sensor made of two different metals, which generates a small DC voltage when heated and is used for temperature measurement.

Type I, II, III assembly: Type I assembly refers to a PCB with surface-mount components on one or both sides. Type II assembly uses a combination of through-hole and surface-mount components, with the through-hole components mounted on the main side and SMD components mounted on one or both sides. Type III assembly is characterized by SMD components mounted on the secondary side and through-hole (pin) components mounted on the main side.

Tombstoning: A soldering defect in which a surface-mount component is pulled up to a vertical position, causing one end to lift off the pad and not solder properly.


Ultra-fine-pitch: Refers to a center-to-center distance and spacing between conductors of 0.010″ (0.25mm) or less for pins or connectors.


Vapor degreaser: A cleaning system in which objects are suspended in a box, and heated solvent vapor condenses onto the surfaces of the objects.

Void: An internal cavity within a solder joint that is formed by trapped gases released or solidified before reflow, often caused by residual flux.


Yield: The ratio of the number of components used in the manufacturing process to the number of components submitted for production at the end of the process.

Please share any missing terms in the comments section.

DiskMFR Field Sales Manager - Leo

It’s Leo Zhi. He was born on August 1987. Major in Electronic Engineering & Business English, He is an Enthusiastic professional, a responsible person, and computer hardware & software literate. Proficient in NAND flash products for more than 10 years, critical thinking skills, outstanding leadership, excellent Teamwork, and interpersonal skills.  Understanding customer technical queries and issues, providing initial analysis and solutions. If you have any queries, Please feel free to let me know, Thanks

DiskMFR Free Sample Application
  • Still worried about storage product quality?
  • Current suppliers can’t provide perfect after-sales service

  • Get our free sample for testing now

Leave a Reply

Your email address will not be published. Required fields are marked *

17 + 12 =

Please let us know what you require, and you will get our reply within 24 hours.

  • Our team will answer your inquiries within 24 hours.
  • Your information will be kept strictly confidential.

Let's Have A Chat

Learn How We Served 100+ Global Device Brands with our Products & Get Free Sample!!!

Email Popup Background 2