Explore the Profab Glossary

AOI (Automated Optical Inspection) uses high-resolution cameras and image-processing software to check assembled boards for defects such as missing, misplaced or mis-oriented components, insufficient solder and bridging. It is typically placed after reflow soldering so process problems are caught before boards move on to test. Because it inspects every board at production speed, AOI generates defect data that feeds directly back into process control.

AS9100D is the current revision of the quality-management standard for the aviation, space and defence industries. It contains the full text of ISO 9001:2015 plus additional aerospace requirements covering areas such as risk management, configuration management, product safety and counterfeit-part prevention. Certification is commonly a prerequisite for supplying electronics into aerospace and defence programmes.

A BGA (Ball Grid Array) is an integrated-circuit package whose connections are an array of solder balls on the underside of the package rather than leads around its edge. BGAs allow high pin counts in a small footprint, but their joints are hidden beneath the package, so they cannot be checked visually and are normally verified by X-ray inspection. Successful BGA assembly depends on accurate placement and a well-controlled reflow profile.

Box build refers to assembly work beyond the bare circuit board: mounting assembled boards into enclosures, routing wiring and cable harnesses, fitting displays, connectors and mechanical parts, and testing the finished unit. The scope varies widely, from a simple board-in-enclosure job to a complete, packaged product ready for distribution. It is also called systems integration or higher-level assembly.

Conformal coating is a thin protective polymer film, commonly acrylic, silicone, polyurethane or epoxy, applied over an assembled board to protect it from moisture, dust, chemicals and condensation. It is widely used for electronics that must survive harsh or outdoor environments. The coating follows the board topography and can be applied by spraying, dipping, brushing or selective automated dispensing, with areas such as connectors kept free of coating.

Counterfeit-part avoidance is the set of purchasing and inspection practices used to keep fraudulent or substandard components out of the supply chain. The core control is buying from franchised distributors or the original manufacturer; when parts must come from independent sources, they receive added scrutiny such as documentation review, visual and X-ray inspection, and electrical testing. AS5553 is the standard commonly referenced for counterfeit-avoidance programmes in aerospace and defence work.

DFM (Design for Manufacturability) is the review of a product design, including board layout, component choices, panelisation and fabrication data, to identify anything that would make it difficult, unreliable or unnecessarily expensive to build in volume. Typical findings include inadequate spacing, poor footprint design, missing fiducials or parts nearing obsolescence. A DFM review is usually done during new product introduction, before stencils and tooling are ordered, when changes are cheapest to make.

EOL (End of Life) is the point at which a component manufacturer discontinues a part, normally announced in advance through a discontinuance notice with a last-time-buy date. Because electronic products often outlive the components inside them, obsolescence management, meaning monitoring EOL notices, making last-time buys and qualifying alternatives, is an ongoing task for any long-running assembly. Unmanaged EOL events are a common cause of redesigns and supply interruptions.

ESD (Electrostatic Discharge) control is the discipline of preventing static electricity from damaging sensitive components during handling, assembly and storage. A discharge too small for a person to feel can degrade or destroy semiconductor devices, sometimes causing latent failures that only appear in the field. Controls include grounded wrist straps, dissipative work surfaces and flooring, shielded packaging and ionisation; ANSI/ESD S20.20 is the widely used standard for ESD-control programmes.

Fine-pitch assembly is the placement and soldering of components whose leads or terminations are very closely spaced, such as fine-pitch quad flat packs and small chip packages. Tighter pitches leave less margin for error in stencil printing and placement, so they demand accurate machines, good stencil design and tight process control. Inspection also becomes more demanding, typically relying on AOI and, for hidden joints, X-ray.

First article inspection (FAI) is the detailed verification of the first unit built with a new design, revision or process against the released documentation. It confirms that the assembly process produces exactly what the drawings and bill of materials specify before the rest of the run is built. In aerospace work FAI is formalised by AS9102, which defines the required report forms.

ICT (In-Circuit Test) uses a bed-of-nails fixture to contact test points on an assembled board and electrically verify individual components and connections, checking for shorts, opens, and wrong, missing or mis-oriented parts. It provides high fault coverage and fast, precise fault location, but requires a custom fixture, so it suits stable, higher-volume products. It is often combined with functional testing, which exercises the finished assembly as a whole to confirm it performs as intended.

IPC-A-610, Acceptability of Electronic Assemblies, is the most widely used inspection standard for assembled circuit boards. It defines, with photographs and illustrations, what constitutes acceptable and defective conditions for solder joints, component placement and assembly workmanship at each product class. Inspectors and operators are commonly trained and certified to it, and purchase orders often cite it together with a required class.

IPC standards group electronic products into three classes that set how stringent the acceptance criteria are. Class 1 covers general electronic products where the main requirement is that the assembly functions; Class 2 covers dedicated-service products needing continued performance and extended life, and is the common default for industrial electronics; Class 3 covers high-performance products where continued operation is critical and failure cannot be tolerated, such as life-support and many aerospace applications. The class is chosen by the customer and drives inspection criteria, process requirements and cost.

J-STD-001, Requirements for Soldered Electrical and Electronic Assemblies, is the industry standard for the materials and processes used to make soldered assemblies. Where IPC-A-610 describes what an acceptable finished assembly looks like, J-STD-001 specifies how it should be built, covering solder materials, fluxes, process requirements and workmanship. The two standards are designed to be used together and share the Class 1, 2 and 3 structure.

Lead time is the elapsed time between placing an order and receiving the goods. In electronics manufacturing it has two main components: material lead time, driven by the longest-lead component on the bill of materials, and production lead time through the factory. Component lead times vary greatly with market conditions, which is why early bill-of-materials review and, for repeat products, forecast-based material buying are used to protect delivery dates.

MOQ (Minimum Order Quantity) is the smallest quantity a supplier will sell of a given item. For electronic components, MOQs often reflect standard packaging such as full reels, so a small production run may require buying far more of a component than the build consumes. The excess either becomes stocked inventory or is priced into the job, which is one reason unit cost falls significantly at higher volumes.

MSDs (Moisture-Sensitive Devices) are plastic-packaged components that absorb ambient moisture; if soldered while damp, the trapped moisture can vaporise during reflow and crack or delaminate the package. J-STD-020 classifies components into moisture-sensitivity levels, and J-STD-033 defines how they must be dry-packed, tracked and baked. In practice this means sealed moisture-barrier bags, a limited floor life once opened, and dry storage or baking before use.

NPI (New Product Introduction) is the structured process of taking a new design from released data to stable production. It typically includes DFM and testability review, quoting and sourcing of the bill of materials, tooling such as stencils and fixtures, prototype and pilot builds, and first article inspection. A disciplined NPI phase finds design and process issues early, when they are cheapest to correct, and shortens the path to reliable volume manufacture.

Pick-and-place is the automated placement stage of surface-mount assembly: machines pick components from reels, trays or tubes and set them onto the printed solder paste at programmed positions on the board. Vision systems check and align each component before placement, allowing very small and fine-pitch parts to be positioned accurately at high speed. Placement accuracy and correct machine programming are major determinants of first-pass yield.

Reflow soldering is the process that forms the solder joints in surface-mount assembly: boards with printed solder paste and placed components pass through a multi-zone oven that gradually preheats the assembly, melts (reflows) the solder and cools it in a controlled way. The temperature-versus-time recipe, known as the reflow profile, is tuned to the solder paste and the components on the board. A poorly controlled profile causes defects such as tombstoning, voiding or component damage, so profiling is a core process control in SMT.

RoHS (Restriction of Hazardous Substances) is the EU directive restricting certain hazardous substances, including lead, mercury, cadmium and specified phthalates, in electrical and electronic equipment. For assembly it chiefly means lead-free solder alloys and compliant components, with documentation to demonstrate compliance. It is often considered alongside REACH, the broader EU chemicals regulation that imposes duties to declare substances of very high concern.

Selective soldering solders through-hole components on otherwise surface-mount boards by applying a small, programmable solder fountain only to the joints that need it. It replaces hand soldering or full wave soldering when a mostly surface-mount board carries a handful of through-hole connectors or parts, giving repeatable, machine-controlled joints without exposing the rest of the assembly to a wave. Programs define flux application, preheat and solder contact for each joint or component.

SMT (Surface-Mount Technology) is the dominant method of electronic assembly, in which components are mounted directly onto pads on the board surface rather than through drilled holes. A standard SMT line prints solder paste through a stencil, places components with pick-and-place machines and forms the joints in a reflow oven. SMT enables the small package sizes, high component density and double-sided assembly that modern products require.

Stencil printing is the first step of the SMT process: a squeegee forces solder paste through laser-cut apertures in a thin metal stencil aligned to the board, depositing a controlled amount of paste on each pad. Paste-deposit quality has an outsized effect on assembly yield, as a large share of SMT defects can be traced back to printing, so aperture design, stencil thickness and print parameters are managed carefully. Many lines add solder paste inspection (SPI) directly after printing to measure deposits before components are placed.

THT (Through-Hole Technology) mounts components by inserting their leads through plated holes in the board and soldering them on the opposite side, by wave, selective or hand soldering. Though largely superseded by SMT for general components, through-hole remains preferred where mechanical strength matters, such as connectors, transformers, large capacitors and parts subject to physical stress. Many modern assemblies are mixed-technology, combining SMT with a small number of through-hole parts.

Traceability is the ability to establish, for any finished unit, what went into it and how it was built: typically which component lots and date codes were used, when it was assembled, and its inspection and test results. It is usually implemented with serial numbers or barcodes scanned at each production stage. Strong traceability limits the scope of recalls and containment actions to the units actually affected, and is a requirement in regulated sectors such as medical and aerospace.

Turnkey and consigned are the two basic commercial models for contract assembly. In a turnkey arrangement the manufacturer sources all components and materials as well as building the product, taking responsibility for the supply chain; in a consigned arrangement the customer supplies the parts, usually as pre-counted kits (kitting), and the manufacturer provides labour and process. Hybrid or partial-turnkey arrangements, where the customer consigns only selected components, are also common.

Wave soldering solders through-hole components in bulk by passing the underside of the assembled board over a standing wave of molten solder, after fluxing and preheating. It was the workhorse of through-hole era production and is still used for boards with substantial through-hole content. On mixed-technology boards, bottom-side surface-mount parts in the wave path must be glued in place and wave-compatible, which is one reason selective soldering has taken over many lower-volume applications.

X-ray inspection uses transmission X-ray imaging to examine solder joints and features that optical inspection cannot see, most importantly the hidden joints under BGAs, QFNs and other bottom-terminated packages. It reveals defects such as voids, bridging, insufficient solder and head-in-pillow conditions. AXI (Automated X-ray Inspection) applies this in-line at production speed, while manual X-ray systems are common for sampling, first article inspection and failure analysis.