EMS & PCB Assembly Glossary
A plain-English guide to the certifications, processes and acronyms you'll see across listings on this directory - useful whether you're sourcing a supplier for the first time or double-checking what a spec sheet actually means.
General terms
| Term | What it means |
|---|---|
| EMS (Electronics Manufacturing Services) | A company that manufactures electronic products or assemblies on a contract basis for other companies, rather than selling its own branded products. |
| CEM (Contract Electronics Manufacturer) | Used interchangeably with EMS - a manufacturer that builds to a customer's design rather than its own. |
| OEM (Original Equipment Manufacturer) | A company that designs and sells its own branded products, as distinct from an EMS/CEM that builds products for other companies. |
| PCB (Printed Circuit Board) | The bare board itself: an insulating substrate with copper traces connecting components, before any parts are fitted. |
| PCBA (Printed Circuit Board Assembly) | A PCB once components have been fitted and soldered onto it. |
| NPI (New Product Introduction) | Taking a product from design/prototype into repeatable, reliable volume manufacture, including design-for-manufacture review and test development. See Prototyping & NPI suppliers. |
| DFM (Design for Manufacture) | Engineering review of a product design to identify and fix issues that would make it difficult, unreliable or expensive to manufacture, before production starts. |
| DFT (Design for Testability) | Designing a board so its assembled state can be effectively tested (e.g. adding test points), rather than testing being an afterthought. |
| Turnkey | A manufacturing arrangement where the assembler sources all components and materials themselves, as opposed to consigned/free-issue, where the customer supplies the parts. |
| Consignment / Free Issue | The customer supplies some or all of the components for the assembler to fit, rather than the assembler sourcing them. |
| Box Build | Assembling a populated PCB into its final housing along with other components (cabling, displays, connectors, mechanical hardware) to produce a complete, tested product. See Box Build Assembly suppliers. |
| Systems Integration | Combining multiple sub-assemblies, PCBs, software and mechanical components into one complete, tested system - typically for larger or more complex products than a simple box build. See Systems Integration suppliers. |
Certifications & accreditations
| Certification | What it means |
|---|---|
| ISO 9001 | The international standard for quality management systems - the most common baseline manufacturing certification. |
| ISO 13485 | The quality management standard specific to medical device manufacturing. |
| ISO 14001 | The international standard for environmental management systems. |
| ISO 45001 | The international standard for occupational health and safety management. |
| ISO 27001 | The international standard for information security management. |
| ISO 50001 | The international standard for energy management systems. |
| ISO 17025 | The international standard for the competence of testing and calibration laboratories. |
| IATF 16949 / TS 16949 | The quality management standard specific to the automotive industry (IATF 16949 superseded the older TS 16949). |
| AS9100 / AS9100D | The quality management standard for the aerospace industry, built on ISO 9001 with additional aerospace-specific requirements (AS9100D is the current revision). |
| AQAP 2110 | A NATO quality assurance standard for defence suppliers, based on ISO 9001. |
| JOSCAR | A shared supplier-accreditation database for the aerospace, defence and security industries. Registration lets buyers in those sectors verify a supplier's credentials in one place rather than each running separate audits. |
| Nadcap | An industry-managed accreditation program for specialised aerospace manufacturing processes (e.g. welding, heat treatment, non-destructive testing). |
| ITAR | US export-control regulations (International Traffic in Arms Regulations) governing defence-related articles and technical data - relevant to suppliers handling US defence work. |
| RoHS | An EU/UK regulation restricting the use of specific hazardous materials (e.g. lead, mercury) in electronic and electrical equipment. |
| REACH | An EU/UK chemicals regulation requiring registration and control of substances of concern used in manufacturing. |
| UL | Product safety certification/listing, commonly seen on electrical and electronic equipment. |
| ATEX | EU/UK certification for equipment used in potentially explosive atmospheres. |
| EN ISO 80079 | A technical standard for equipment used in explosive atmospheres, often referenced alongside ATEX certification. |
| EMAS | A voluntary EU environmental management scheme, more rigorous than ISO 14001 alone. |
| IRIS | A quality management standard specific to the rail industry. |
| TL 9000 | A quality management standard specific to the telecommunications industry. |
| ISO 18001 / OHSAS 18001 | An older occupational health and safety management standard, largely superseded by ISO 45001. |
| Cyber Essentials / Cyber Essentials Plus | A UK government-backed certification demonstrating basic (Plus: independently verified) cyber-security controls. |
Workmanship & assembly standards (IPC)
| Standard | What it means |
|---|---|
| IPC | The trade association that publishes the workmanship and design standards below for the electronics manufacturing industry. |
| IPC-A-600 | Defines acceptability criteria for bare (unpopulated) printed circuit boards. |
| IPC-A-610 | Defines acceptability criteria for populated PCB assemblies - the most widely referenced workmanship standard in the industry. Often held to Class 2 (general electronics) or the stricter Class 3 (aerospace, defence, medical). |
| IPC J-STD-001 | Covers the actual soldering process requirements for electrical and electronic assemblies, as distinct from A-610's finished-assembly inspection criteria. |
| IPC/WHMA-A-620 | The wire-harness equivalent of IPC-A-610 - defines acceptability of cable and wire harness assemblies. |
| IPC-7711/21 | Covers rework, repair and modification of electronic assemblies. |
| IPC-1791 | A trusted electronic designer/manufacturer certification, aimed at counterfeit-component risk and supply-chain security. |
| IPC-CC-830 | Covers conformal coating materials used to protect assembled PCBs. |
Assembly types & board construction
| Term | What it means |
|---|---|
| SMT (Surface Mount Technology) | Components are soldered directly onto the surface of the board, rather than through drilled holes - the dominant assembly method for modern electronics. |
| THT (Through-Hole Technology) | Component leads are inserted through drilled holes in the board and soldered on the other side - still used for components needing more mechanical strength. |
| Mixed Technology | A board using both surface-mount and through-hole components. |
| Press-Fit | Components (often connectors) mechanically pressed into plated holes rather than soldered. |
| Rigid / Flexible / Rigid-Flex | Board construction types: a standard solid board, a bendable board, or a hybrid combining both rigid and flexible sections in one assembly. |
| HDI (High-Density Interconnect) | A PCB construction using finer traces, smaller vias and higher connection-pad density than standard boards, to fit more circuitry into less space. |
| Metal-based / Ceramic | Alternative board substrate materials (instead of standard fibreglass) used for their heat-dissipation or high-reliability properties. |
Package types (component packaging)
| Package | What it means |
|---|---|
| BGA (Ball Grid Array) | A component package with solder balls on its underside rather than leads around the edge, used for high pin-count chips. |
| Micro-BGA / CSP | Miniaturised BGA-style packages, close to the size of the bare silicon die itself. |
| QFN / QFP | Square/rectangular chip packages with contacts on (QFN) or leads extending from (QFP) all four sides. |
| LGA (Land Grid Array) | Similar to BGA but using flat contact pads instead of solder balls. |
| DFN (Dual Flat No-lead) | A smaller, two-sided version of the QFN package style. |
| SOIC | A common surface-mount package with leads along two sides. |
| DIP (Dual In-line Package) | A classic through-hole package with two parallel rows of pins. |
| TQFP / TSSOP | Thin variants of QFP and SOIC packages respectively, for lower-profile assemblies. |
| PLCC | A square surface-mount package with J-shaped leads on all four sides. |
| PBGA / CBGA / TBGA | BGA variants distinguished by substrate/carrier material (plastic, ceramic, tape). |
| POP (Package on Package) | Two or more component packages stacked vertically and interconnected, saving board space. |
| WLCSP / DSBGA | Wafer-level and die-size BGA packages - among the smallest and most compact chip packaging formats. |
| Flip Chip | A chip mounted face-down directly onto the board or substrate, connected via solder bumps rather than wire bonds. |
| COB (Chip on Board) | A bare, unpackaged chip die mounted and wire-bonded directly onto the board, then typically encapsulated. |
| FPGA | A field-programmable gate array - a type of chip reconfigurable after manufacture. |
Soldering processes
| Process | What it means |
|---|---|
| Reflow Soldering | Solder paste is applied, components placed, then the whole board is heated to melt and re-solidify the paste - the standard SMT soldering process. |
| Wave Soldering | The underside of a populated board is passed over a wave of molten solder, typically used for through-hole assemblies. |
| Selective Soldering | A targeted, computer-controlled alternative to wave soldering that solders only specific joints, used when a board mixes SMT and through-hole components. |
| Hand Soldering | Components soldered manually, typically for low-volume, prototype or rework. |
| Robotic Soldering | Automated, programmable soldering (often a robotic arm performing selective soldering) rather than a manual or mass-wave process. |
| Lead-Free (RoHS) Solder | Solder alloy without lead, required for RoHS-compliant products. |
| Leaded / Tin-Lead Solder | Traditional tin-lead solder alloy, still used where lead-free isn't required or suitable (e.g. certain aerospace/defence, or legacy repair work). |
Testing & inspection
| Test | What it means |
|---|---|
| AOI (Automated Optical Inspection) | A camera-based system that automatically inspects assembled boards for defects (missing components, solder bridges, misalignment). |
| SPI (Solder Paste Inspection) | Automated inspection of solder paste deposits before components are placed, catching print defects early in the process. |
| X-Ray Inspection | Used to inspect solder joints hidden underneath a component (such as BGA balls) that can't be seen by optical inspection. |
| ICT (In-Circuit Testing) | A test using a fixture with many probe points to check individual components and connections on an assembled board electrically. |
| Flying Probe Testing | An alternative to ICT using moving probes instead of a fixed test fixture, useful for lower volumes or where a custom fixture isn't justified. |
| Functional Testing | Testing the assembled product as a whole to confirm it performs its intended function, rather than testing individual components. |
| Boundary Scan Testing | Uses built-in circuitry on modern chips to test connections without needing physical probe access to every point. |
| Hi-Pot (High Potential) Testing | Applies a high voltage between conductors to check insulation integrity and detect faults that could cause a safety hazard. |
| Burn-In Testing | Running an assembled product under load for an extended period to catch early-life component failures before shipment. |
| Environmental Testing | Testing a product's performance under conditions such as temperature, humidity or vibration extremes. |
| Soak Testing / Thermal Aging Testing | Extended-duration testing (often under heat) to reveal failures that only appear over time. |
| Component Value Check | Verifying that the correct component values (resistance, capacitance etc.) have been fitted, sometimes distinct from full functional test. |
Cable & harness assembly
| Term | What it means |
|---|---|
| Wire Harness / Loom | A bundled, often multi-branch assembly of wires and cables connecting several points in a system, as distinct from a single discrete cable assembly. See Cable & Wire Assembly suppliers. |
| Discrete Cable Assembly | Typically a single cable with a connector at each end, rather than a multi-branch harness. |
| Crimping | Mechanically attaching a connector terminal to a wire by compressing it, rather than soldering. |
| Heat-Shrink / Sleeving | Heat-shrinkable tubing applied over wire joints or bundles for insulation, strain relief or bundling. |
Box build & procurement terms
| Term | What it means |
|---|---|
| Electro-Mechanical Assembly | Combining electronic components (boards, wiring) with mechanical parts (motors, switches, housings) into one working assembly. See Electromechanical Assembly suppliers. |
| Potting / Encapsulation | Filling an assembly with a resin or compound for protection against moisture, vibration or chemical exposure. |
| Conformal Coating | A thin protective coating (acrylic, polyurethane, silicone or parylene) applied over a populated board to protect against moisture, dust and corrosion. |
| Obsolescence Management | Proactively managing and sourcing replacements for components that go out of production during a product's manufacturing life. |
Trade bodies & industry schemes
These are industry affiliations, not corporate ownership - a company can be a member without being part of a corporate group.
| Term | What it means |
|---|---|
| ADS Group | The UK trade association for the Aerospace, Defence, Security and Space industries. |
| CERN Accredited Supplier | A supplier approved to bid for and deliver contracts to CERN, the European particle physics laboratory - a procurement-approval status rather than a manufacturing certification. |
Spotted a term that should be added, or something that reads unclearly? Let us know at ems@emsdirectory.co.uk.