PCB Terminology List in PCB Design-PCB Glossary

Introduction to PCB Terminology

Printed Circuit Board (PCB) design involves a wide range of technical terms and acronyms. Understanding the common PCB terminology is crucial for effective communication among PCB designers, manufacturers, and clients. This comprehensive PCB glossary serves as a reference guide to help you navigate the complex world of PCB design and manufacturing.

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PCB Glossary

A

Annular Ring: The copper pad surrounding a drilled hole on a PCB.
Aspect Ratio: The ratio of a PCB’s thickness to the diameter of the smallest drilled hole.

B

BGA (Ball Grid Array): A surface-mount package with a grid of solder balls on the bottom for connection to the PCB.
Blind Via: A via that connects an outer layer to an inner layer, but does not go through the entire board.

C

Copper Thickness: The thickness of the copper foil laminated onto the PCB substrate, typically measured in ounces per square foot (oz/ft²).
Creepage: The shortest distance between two conductive parts along the surface of the PCB.

D

DFM (Design for Manufacturability): The process of designing a PCB to ensure efficient and cost-effective manufacturing.
Drill Hit: The location where a drilled hole intersects with a copper pad or trace.

E

ECO (Engineering Change Order): A document that specifies changes to be made to a PCB design after the initial design is complete.
EMI (Electromagnetic Interference): Unwanted electromagnetic energy that can interfere with the proper operation of electronic devices.

F

Fab Drawing: A detailed drawing that provides all the necessary information for manufacturing a PCB.
Fiducial: A reference mark on a PCB used for aligning the board during assembly.

G

Gerber File: A standard file format used to describe the layout of a PCB for manufacturing.
Ground Plane: A large area of copper on a PCB layer that provides a low-impedance return path for electrical currents.

H

HDI (High Density Interconnect): A PCB design technique that involves using small vias, fine pitch components, and multiple layers to achieve high component density.
Hole Size: The diameter of a drilled hole in a PCB.

I

Impedance Control: The process of designing a PCB to maintain a specific characteristic impedance for high-speed signals.
IPC (Institute of Printed Circuits): A global trade association that develops standards for the electronic interconnect industry.

J

Junction Temperature: The temperature at the junction of a semiconductor device mounted on a PCB.

K

Keepout: An area on a PCB where components or copper traces are not allowed.

L

Laminate: The insulating material used as the base substrate for a PCB, typically made of FR-4.
Layer Stack: The arrangement of copper layers and insulating layers in a multi-layer PCB.

M

Mask: A thin protective coating applied to a PCB to prevent oxidation and provide electrical insulation.
Microvia: A small via with a diameter less than 6 mils (0.15 mm) used in HDI PCB designs.

N

Necking: The narrowing of a PCB trace to pass between closely spaced pads or vias.
Net: A group of interconnected component pins or pads in a PCB design.

O

OSP (Organic Solderability Preservative): A surface finish applied to exposed copper on a PCB to prevent oxidation and enhance solderability.
Outer Layer: The top and bottom layers of a multi-layer PCB.

P

Pad: A copper area on a PCB used for soldering components or making electrical connections.
Panelization: The process of arranging multiple PCB designs on a single panel for efficient manufacturing.

Q

QFP (Quad Flat Package): A surface-mount package with leads on all four sides.

R

Reflow Soldering: A process of soldering components to a PCB by applying solder paste and heating the board in a reflow oven.
Routing: The process of creating copper traces on a PCB to connect components according to the schematic.

S

Schematic: A graphical representation of the electrical connections and components in a PCB design.
Silkscreen: The text and symbols printed on a PCB for component identification and assembly instructions.
SMD/SMT (Surface Mount Device/Technology): Components and methods used for mounting components directly onto the surface of a PCB.
Solder Mask: A protective coating applied to a PCB to prevent solder bridges and protect against oxidation.

T

Thermal Relief: A pattern of copper around a hole or pad that helps dissipate heat during soldering.
Thermocouple: A temperature sensor used for monitoring the temperature of a PCB during testing or operation.
Through-hole: A type of component that is mounted by inserting its leads through holes drilled in the PCB.
Trace: A thin copper path on a PCB that connects components electrically.
Trace Width: The width of a copper trace on a PCB, typically measured in mils (thousandths of an inch).

U

UL (Underwriters Laboratories): An independent safety certification organization that tests and certifies PCBs and electronic components.

V

Via: A plated hole that connects copper traces on different layers of a multi-layer PCB.
Via in Pad: A via drilled directly through a component pad, allowing for more compact PCB designs.

W

Wave Soldering: A process of soldering through-hole components to a PCB by passing the board over a wave of molten solder.

X

X-Out: A marking on a PCB to indicate that a component should not be placed during assembly.

Y

Yield: The percentage of PCBs that pass all manufacturing and testing requirements.

Z

Impedance: The measure of opposition to the flow of alternating current in a circuit, expressed in ohms (Ω).

PCB Layer Stackup

A PCB layer stackup refers to the arrangement of copper layers and insulating layers in a multi-layer PCB. The number of layers and their arrangement can vary depending on the complexity and requirements of the PCB design. Here’s an example of a typical 4-layer PCB stackup:

Layer	Material	Thickness (mm)
Top Copper	Copper	0.035
Prepreg	FR-4	0.2
Inner Layer 1	Copper	0.018
Core	FR-4	0.5
Inner Layer 2	Copper	0.018
Prepreg	FR-4	0.2
Bottom Copper	Copper	0.035

In this example, the top and bottom layers are the outer layers, while the two inner layers are embedded within the PCB. The prepreg and core materials are made of FR-4, which is a flame-retardant glass-reinforced epoxy laminate commonly used in PCB manufacturing.

PCB Surface Finishes

PCB surface finishes are applied to the exposed copper on a PCB to prevent oxidation, enhance solderability, and protect the copper from environmental factors. Some common PCB surface finishes include:

Surface Finish	Composition	Thickness (µm)	Shelf Life
HASL (Hot Air Solder Leveling)	Sn60/Pb40 or Sn99.3/Cu0.7	1-40	12 months
ENIG (Electroless Nickel Immersion Gold)	Ni (120-240 nm) / Au (0.05-0.12 µm)	0.05-0.12	12 months
OSP (Organic Solderability Preservative)	Organic compounds	0.2-0.5	6-12 months
Immersion Tin	Sn (100%)	0.8-1.5	12 months
Immersion Silver	Ag (100%)	0.1-0.3	12 months

Each surface finish has its advantages and disadvantages in terms of cost, durability, and compatibility with different soldering processes.

Frequently Asked Questions (FAQ)

What is the difference between a schematic and a PCB layout?
A schematic is a graphical representation of the electrical connections and components in a PCB design, while a PCB layout is the physical arrangement of those components and connections on the actual PCB.
What is the purpose of a solder mask on a PCB?
A solder mask is a protective coating applied to a PCB to prevent solder bridges, protect against oxidation, and provide electrical insulation between closely spaced pads and traces.
What is the difference between through-hole and surface-mount components?
Through-hole components have leads that are inserted through drilled holes in the PCB and soldered on the opposite side, while surface-mount components are mounted directly onto the surface of the PCB and soldered in place.
What is the role of vias in a multi-layer PCB?
Vias are plated holes that connect copper traces on different layers of a multi-layer PCB, allowing for more complex routing and higher component density.
What is the importance of impedance control in PCB design?
Impedance control is crucial in high-speed PCB designs to ensure signal integrity and prevent issues like reflections, crosstalk, and signal distortion. By maintaining a specific characteristic impedance for critical traces, designers can minimize these problems and ensure reliable performance.

Conclusion

Understanding PCB terminology is essential for anyone involved in PCB design, manufacturing, or procurement. This comprehensive PCB glossary covers a wide range of terms, from basic concepts to advanced techniques, and serves as a valuable reference for professionals and enthusiasts alike. By familiarizing yourself with these terms, you can communicate more effectively, make informed decisions, and ultimately create better PCB designs.