PCB Glossary

As a UK supplier of high-quality printed circuit boards, we’re dedicated to delivering solutions that cater to our customers' specific needs. This glossary serves as a valuable reference for key PCB and electronics terms, covering everything from technical specifications to compliance documentation. Explore the definitions below to gain insights into the materials, processes, and standards that define the PCB industry!

Technical PCB Terms -

Multilayer PCB

PCB with multiple layers of conductive material separated by insulating layers (dielectric). These layers are laminated together to increase circuit density. Typical uses include advanced telecommunications, aerospace, and military applications.

Layer Build-Up

The sequence of alternating copper and dielectric layers in a multilayer PCB. A common build-up might include signal layers, power planes, and ground layers to facilitate complex circuit routing.

Solder Resist (Solder Mask)

A protective lacquer-like layer applied to PCBs to prevent solder bridges and protect copper traces. Various types include:

Standard Solder Mask: Used in most PCBs. Typically green, though other colors are available.
High-Temperature Solder Mask: Designed to withstand higher temperatures without degrading, often used in automotive or high-power applications.
UV Curable Solder Mask: Cured using ultraviolet light, offering fast processing times.
Peelable Solder Mask: Temporarily applied to protect areas of the board during soldering, then peeled off after the process.

FR-4

A widely used flame-retardant material for PCBs. It consists of woven fiberglass fabric and an epoxy resin binder. FR-4 is known for its excellent mechanical and electrical properties and is used in standard multilayer PCBs.

High-Temperature Materials

Rogers 4350B: A low-loss material that can operate at higher temperatures than FR-4. Often used in RF and microwave applications.
Polyimide: A material known for its ability to endure extremely high temperatures (up to 260°C), commonly used in aerospace and military applications.
Teflon (PTFE): Known for its low dielectric constant and loss tangent, suitable for high-frequency applications and high temperatures.

HDI (High-Density Interconnect)

A PCB with a higher wiring density per unit area. HDI boards have finer lines and spaces, smaller vias, and capture pads to accommodate more components on the board. HDI technology is commonly used in mobile devices and high-performance computing systems.

Vias

Small holes drilled through the layers of a PCB to connect different layers. Types include:

Through-Hole Vias: Drilled through all layers.
Blind Vias: Connect outer layers to internal layers without passing through the entire board.
Buried Vias: Connect only internal layers and are invisible from the board’s surface.
Microvias: Extremely small vias used in HDI boards.

Surface Finish

The coating applied to exposed copper pads to protect them from oxidation and to ensure solderability. Common finishes include:

HASL (Hot Air Solder Leveling): A traditional surface finish that leaves a thin layer of tin-lead. These days Lead free HASL is the industry standard.
ENIG (Electroless Nickel Immersion Gold): Provides a flat surface with excellent solderability and is RoHS-compliant.
OSP (Organic Solderability Preservative): A thin, organic coating applied to copper pads, offering a lead-free solution.

PCB Types & Variations

Rigid PCBs

Made from a solid substrate, these PCBs are inflexible. Common in computers and consumer electronics, rigid PCBs offer durability and performance at a low cost.

Flexible PCBs (Flex PCBs)

Rigid-Flex PCBs

A combination of rigid and flexible circuits in one board. Used in complex devices where reliability and space efficiency are paramount, such as in medical and military equipment.

Metal Core PCB (MCPCB)

A type of PCB with a metal base (typically aluminum) used to enhance heat dissipation. Commonly used in LED applications, power supplies, and automotive electronics.

Compliance & Documentation Terms

RoHS Directive (Restriction of Hazardous Substances)

A European Union directive restricting the use of specific hazardous materials in electronic and electrical equipment. Materials restricted include lead (Pb), mercury (Hg), cadmium (Cd), and hexavalent chromium (Cr6+). PCBs compliant with RoHS use lead-free finishes, such as ENIG or OSP.

REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals)

A regulation of the European Union addressing the production and use of chemical substances, and their potential impacts on human health and the environment. Companies must track and report hazardous substances in their products, including PCBs.

UL Approval

UL (Underwriters Laboratories) certification ensures that products, including PCBs, comply with safety standards. UL 94, for example, is a standard for the flammability of plastic materials, and many PCBs are marked as "UL94-V0" certified, meaning they have passed specific fire retardancy requirements.

IPC Standards

IPC standards are globally recognized guidelines for PCB design, manufacture, and assembly. Common standards include:

IPC-A-600: Acceptance criteria for printed boards.
IPC-6012: Qualification and performance specification for rigid PCBs.
IPC-2221: Generic standard for PCB design.

C of C (Certificate of Conformity)

A document provided by the manufacturer, certifying that the product complies with the required specifications, standards, or regulations.

D of C (Declaration of Conformity)

A formal statement declaring that a product meets all applicable legal and regulatory requirements. For instance, a D of C would accompany a RoHS-compliant PCB to assert compliance with the RoHS directive.

ISO 9001 Certification

Pb-Free (Lead-Free)

Refers to the absence of lead in electronic components and PCBs. The move to lead-free PCBs aligns with RoHS and other environmental regulations to reduce hazardous materials in electronics manufacturing.