Custom Printed Circuit Board (PCB) Assembly Glossary

Check out oPCB custom PCB assembly in the UKur handy glossary of terms related to custom printed circuit board (PCB) assembly. And if you can’t find the information you require please do get in touch.

Active component: semiconductor devices that change their characteristics when placed in a powered circuit on a PCB, i.e. become active.

Annular ring: the annular ring is the width of a conductor pad on a PCB that surrounds a drilled hole.

Assembly: assembly is where components are added to a ‘bare’ composite board to give the printed circuit board its functionality.

Aspect ratio: this aspect ratio is the ratio between the printed circuit board thickness and the smallest drilled hole size of the PCB.

Automated test equipment (ATE):  Automated test equipment is equipment that tests the PCB’s functionality (normally in its assembled state).

Ball grid array (BGA): A ball grid array is a type of surface-mount packaging (a chip carrier) used for integrated circuits. BGA packages are used to mount devices such as microprocessors. A BGA can provide more interconnection pins than can be put on a dual in-line or flat package.

Bare PCB: An bare PCB is an unassembled printed circuit board.

Blind via: a blind via connects an outer layer to an inner layer, but does not go through the whole board. We usually avoid using blind or buried vias in commercial application PCBs because of the higher cost. An eight-layer PCB will often be cheaper than a four-layer PCB with blind or buried vias.

Bill of materials (BOM): The BOM is a listing showing all the components (with the manufacturer’s part numbers and normally PCB references) for the printed circuit board to be assembled. At CDT, we prefer BOM’s being sent using our template; we can supply a copy of this if you contact us.

Chip on board (COB): A chip on board is a wafer of silicon that is assembled directly to the printed circuit board by the use of solder or conductive adhesive.

Printed circuit board assembly: Printed circuit board assembly, also known as PCBA, is the process of soldering or assembly of electronic components to a PCB or printed circuit board.

Circuit board assembly: Printed circuit board assembly, also known as printed circuit board assembly (PCBA), is the process of soldering or assembly of electronic components to a PCB or printed circuit board. The electronic components connect with the wirings of printed circuit boards. The traces or conductive pathways engraved in the laminated copper sheets of PCBs are used within a non-conductive substrate to form the assembly. Lastly attaching the electronic components with the printed circuit boards is the final element before the electronic device is fully operational.

Components: Components are the individual units that added to the board; they give it its functionality.

Coating: This is a thin layer of resin that is applied to the PCB to protect the PCB from its environment.

Coefficient of thermal expansion (CTE): The CTE is a ratio of dimensional change of the PCB to the original dimension when the temperature changes. Can be expressed as stretch or shrink of the bare PCB.

Copper: Copper is a conductor on PCBs. A copper foil can be either laid on one side for a single-sided PCB and both sides for a double-sided board.

Small scale custom PCB assembly: Often low volume or small scale PCB assembly projects are best suited to UK based PCB assembly providers like CDT as it is more cost-effective than going abroad. Typically, this is less than 1000 and quantities in the low hundreds optimal.

Dry film solder mask (DFSM): A dry film solder mask is a thin lacquer-like layer of polymer. It is usually applied to the copper traces of a printed circuit board (PCB) for protection against oxidation and to prevent solder bridges from forming between closely spaced solder pads.

Dual inline package (DIP): Dual inline package is where two rows of pins on the opposite side of a device make the connection with the printed circuit board.

Double sided assembly: Double sided assembly PCB assembly is where there are components on both side of the bare PCB.

Design for manufacturability (DFM) checks: This check determines if there are any design flaws or potential issues before manufacturing starts. It can spot errors and potentially streamline and save money by identifying areas where the design could be made more efficient.

Design rule check (DRC): A design rule check is carried out to make sure the data given to build a PCB follows good practice. The happens before the artworks are made to produce the printed circuit board.

Dry film: Dry film is a polymer-coated polyester film that is sensitive to UV light. It is used to print circuit boards using photolithography.

Edge connector: This is a connector on the edge of a printed circuit board quite often plated with gold to connect the PCB with another PCB or electronic device.

Edge clearance: The edge clearance is the smallest distance a component or track is from the edge of a PCB.

Electronics assembly: in the UK electronics assembly encompasses a wide range of specialist assembly services including PCB assembly with surface mount technology (SMT) and/or conventional technology (THT), as well as regulatory and compliance directives like RoHS, FDA, ISO standards and CE registration requirements.

Etchant: Etchant is a corrosive chemical used to etch a design into the circuit board.

Footprint: A footprint is the layout of pads or holes used to connect a component to a circuit board electrically.

Gerber file: The Gerber file format is an open ASCII vector format for printed circuit board (PCB) designs. It is the de facto standard used by PCB industry software to describe the printed circuit board images. At CDT, our specialists will review your Gerber files before quoting on a project to see if we can help you to improve performance or reliability, or to reduce costs.

Hot air solder leveling (HASL): Hot air solder leveling is a common type of finish used on printed circuit boards. The PCB is usually dipped into a bath of molten solder thereby covering all of the exposed copper surfaces with solder. The excess solder is removed by passing the PCB between hot air knives.

Ident layers or legends: Ident layers are added to the PCB to identify components, test points and parts and to add symbols, logos and warnings. It’s sometimes referred to as Silk-Screening. However, at CDT, we do not suggest printing legend ink on component pads.

Jig: A jig is a type of custom-made tool that is used to control the location and/or motion of parts or other tools. They are used to test PCBs. They contain a dump board which can find faults within the PCB.

Laminate: The laminate of the PCB is what holds the layers together. A PCB is like a layer cake or lasagne, i.e. there are alternating layers of different materials which are laminated together with heat and adhesive to create a single object. Usually, four layers make up the board: substrate, copper, soldermask and silkscreen. The composite or bare boards used to build to PCBs are often called the laminate.

Multi-layer PCB boards: When printed circuit boards require more than one layer of composite, they are called multi-layer boards.

Node: A node is any point on a circuit where the terminals of two or more circuit elements meet on a printed circuit board.

PCB board assembly: In PCB board assembly, the bare board is populated (or stuffed) with electronic components to form a functional printed circuit assembly (PCA). Sometimes also called printed circuit board assembly.

PCB assembly  (PCBA) service: The term PCB is often used to describe the finished board that is fitted into an electronic device. However,  it is, in fact, a printed circuit board assembly which is the PCB plus all of the assembled components.

Pick and place: Machines have replaced manual pick and place, which has ensured accuracy and greater efficiency. Traditionally components were placed on the board by hand using tweezers. Parts are placed directly to the soldered areas (using dots of glue when wave soldering) in preparation for the soldering process.

Plated through hole: This is a hole on a board which has an annular ring and which is plated through the board. It may be a connection point for a through hole component, a via to pass a signal through, or a mounting hole

Printed circuit board assembly: Printed circuit board assembly is a multiple-step process that enables signals and power to be routed between physical devices. Solder is the metal that makes the electrical connections between the surface of the PCB and the electronic components.

Quote: A quote is an estimation of the cost of a PCB assembly run. At CDT, we take time at the outset to ensure that your quote accurately reflects all the elements involved in the project, so there are no surprises down the line.

Reflow soldering:  Reflow soldering is widely used to attach surface mount components to printed circuit boards (PCBs).  The process forms acceptable solder joints by first pre-heating the components/PCB/solder paste and then subjecting the assembly to controlled heat without causing damage by overheating.

RoHS-compliant PCB assembly services: This legislation developed in the EU is also known as Directive 2002/95/EC. It prohibits the use of hazardous materials in electronic products. This directive applies to electronics products sold in EU countries after July 1, 2006. Anyone who makes and sells electronic products (or components such as printed circuit boards) to Europe must adhere to it. The use of six materials in the PCBs and electronic items is restricted. They include mercury, cadmium, hexavalent chromium, polybrominated diphenyl ethers, polybrominated biphenyls, lead and phthalates (like BBP, DEHP, BBP, and DIBP).

Schematic: A schematic is a drawing or sketch showing how a system works at an abstract level. A circuit diagram (electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. It illustrates the electrical connection between active and passive components.

Solder mask: A solder mask or stop is a thin lacquer-like layer of polymer. It is usually applied to the copper traces of a printed circuit board (PCB) to protect against oxidation and to prevent solder bridges from forming between closely spaced solder pads. The characteristic green colour associated with PCBs comes from the solder mask, which keeps everything in place and prevents shorts by insulating copper traces from other conductive materials on the board. The solder mask also contains holes, which serve two purposes: to allow components to be soldered to the board and to protect the rest of the board from solder.

Solder paste: Solder paste is a material used in the manufacture of printed circuit boards to connect surface mount components to pads on the board. It is applied to the board using either a machine or manually through a stencil to ensure that the paste is applied where needed.

Silkscreen: The silkscreen is an essential layer on a PCB. It contains all of the printed information in symbols and characters that indicate each component’s function. This layer is often applied on the component side; however, using it on the solder side is also not uncommon.

Surface mount PCB assembly: As the name suggests, this technology mounts electronic components to the surface of the printed circuit board (PCB). As opposed to inserting components through holes as with conventional assembly. Surface mount PCB assembly services are increasingly popular and have largely replaced the through-hole method of fitting components. They are not only more reliable and usually more cost-effective. But also enable more electronics to be packed into a much smaller space, thus resolving the space issues associated with through-hole mounting.

Underside: This is the bottom of the printed circuit board. Usually, this is the side without components and the side that touches the solder wave during assembly, which is why it is sometimes also called the solder side. However, PCBs are often populated on both sides, and the assembly process does not require wave soldering. Hence the bottom side is a clearer definition to use to avoid confusion.

Wave solder machine: This machine enables a bulk soldering process that is used in the manufacture of printed circuit boards. The circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave.  Wave Soldering is used mainly in the through-hole manufacturing process.

Wave soldering: This process places the assembled printed circuit boards into contact with a constantly flowing and circulating mass of solder


Here to Help….

Our ethos here at CDT in Brackley is all about providing a value-added PCB design, prototyping and production service. We do this by sharing our tried and tested PCB assembly knowledge with customers to help minimise any stress and project uncertainty. So if you have a question or would like to ask a PCB expert – do get in touch with us.