PCB Terminology Glossary
Comprehensive guide to PCB design and manufacturing terminology.
A
Annular Ring
The area of copper pad remaining after a hole is drilled. Minimum annular ring affects manufacturing yield.
AOI
Automated Optical Inspection. Camera-based quality check for solder joints and components.
Aspect Ratio
The ratio of board thickness to drilled hole diameter. Higher ratios are more challenging to manufacture.
B
BGA
Ball Grid Array. A surface mount package with solder balls arranged in a grid pattern on the bottom.
Blind Via
A via that connects an outer layer to one or more inner layers but doesn't go through the entire board.
BOM
Bill of Materials. A list of all components required for PCB assembly.
Buried Via
A via that connects inner layers only and is not visible from either surface of the board.
C
CAM
Computer Aided Manufacturing. Software used to prepare design files for PCB fabrication.
Castellated Holes
Half-holes at board edges used for edge-mounting modules or as test points.
Clearance
The minimum distance between conductive elements (traces, pads, copper pours).
Conformal Coating
Protective coating applied to assembled PCB for moisture and contamination protection.
Controlled Impedance
Traces designed to have a specific impedance value, critical for high-speed signals.
Copper Pour
Large area of copper fill, typically connected to ground or power, also called copper plane.
Copper Weight
Thickness of copper foil, measured in oz/ft². 1 oz = 35 μm = 1.378 mil.
Core
A rigid laminate with copper on one or both sides, forming the base of a multilayer PCB.
Creepage
The shortest distance along a surface between two conductors. Important for high voltage designs.
Crosstalk
Unwanted coupling of signals between adjacent traces.
D
DFA
Design for Assembly. Design practices that optimize PCB assembly process.
DFM
Design for Manufacturing. Design practices that ensure the PCB can be reliably manufactured.
Dielectric
Non-conductive material between copper layers, typically FR4 or high-frequency laminates.
Differential Pair
Two traces carrying opposite polarity signals, used for high-speed data transmission.
DRC
Design Rule Check. Automated verification that design meets manufacturing constraints.
Drill Hit
A single drilling operation on the PCB. Total drill hits affect manufacturing time and cost.
E
ENIG
Electroless Nickel Immersion Gold. A surface finish with nickel barrier and thin gold layer.
F
Fiducial
Reference marks on PCB for automated pick-and-place machine alignment.
Flying Probe
Test method using moving probes to check electrical connectivity without fixed fixtures.
FR4
Flame Retardant 4. The most common PCB substrate material, glass-reinforced epoxy.
G
Gerber
Standard file format for PCB fabrication data, defining copper layers, soldermask, etc.
H
HASL
Hot Air Solder Leveling. Surface finish process using molten solder and hot air.
I
ICT
In-Circuit Test. Electrical test using bed-of-nails fixture to verify component values.
Impedance
Total opposition to current flow in AC circuits, measured in ohms. Critical for signal integrity.
Inner Layer
Copper layers inside a multilayer PCB, not visible from the outside.
L
Laminate
The base material of PCB consisting of resin and reinforcement (typically glass fiber).
M
Microstrip
A trace on outer layer with reference plane below, common for controlled impedance.
N
NPTH
Non-Plated Through Hole. A hole without copper plating, used for mounting.
O
OSP
Organic Solderability Preservative. Water-based organic surface finish.
P
Pad
A copper area designed for component lead attachment, either for SMD or through-hole.
Pick and Place
Automated machine that places SMD components on PCB before reflow soldering.
Prepreg
Pre-impregnated fiberglass with uncured resin, used to bond core layers in multilayer PCBs.
PTH
Plated Through Hole. A hole with copper plating connecting layers.
R
Reflow
Soldering process where solder paste is melted in an oven to attach SMD components.
Return Path
The path current takes to return to source, ideally directly beneath the signal trace.
S
Signal Integrity
The quality of an electrical signal, affected by impedance, crosstalk, and reflections.
Silkscreen
Layer of ink on PCB showing component designators, logos, and other markings.
Skew
Time difference between signals that should arrive simultaneously, critical in differential pairs.
Solder Paste
Mixture of tiny solder particles and flux, applied to pads before component placement.
Soldermask
Protective layer covering copper except where soldering is needed, typically green.
Stackup
The arrangement of copper and dielectric layers in a multilayer PCB.
Stencil
Thin metal sheet with apertures used to apply solder paste to PCB pads.
Stripline
A trace on inner layer between two reference planes, providing better shielding.
Surface Finish
Coating applied to exposed copper to prevent oxidation and ensure solderability.
T
Teardrop
Gradual widening where trace meets pad, improving reliability at connection point.
Thermal Relief
A pattern connecting a pad to a copper pour that aids soldering by limiting heat dissipation.
Trace
A pathway of copper connecting components, also called track or conductor.
V
Via
A plated hole connecting copper on different layers of a PCB.
Via-in-Pad
A via placed within a component pad, often filled and plated over for BGAs.
W
Wave Soldering
Process where PCB passes over a wave of molten solder for through-hole components.
X
X-Ray Inspection
Non-destructive testing to inspect solder joints under BGA and other hidden areas.