PCB & PCBA Glossary
Plain-English definitions of 29+ PCB assembly terms. Use the search box to find any term.
AOI (Automated Optical Inspection)
Machine vision system that photographs assembled PCBs and compares them to a reference image to detect solder defects, missing components, and placement errors.
BGA (Ball Grid Array)
IC package where solder balls on the underside of the package form the electrical connections. Requires X-ray inspection to verify solder joint quality.
BOM (Bill of Materials)
List of all components required to build a PCB assembly, including reference designators, quantities, part numbers, and descriptions.
Centroid File
Also called pick and place file or CPL. Contains X/Y coordinates, rotation, and side (top/bottom) for each component, used to program SMT placement machines.
Conformal Coating
Thin protective coating applied to assembled PCBs to protect against moisture, dust, chemicals, and temperature extremes. Types: acrylic, silicone, polyurethane, epoxy.
CSP (Chip Scale Package)
IC package where the package size is close to the die size. Similar assembly challenges to BGA — requires X-ray inspection.
DFM (Design for Manufacturability)
Process of reviewing a PCB design to identify features that may cause manufacturing problems, and recommending changes to improve yield and reduce cost.
DNP / DNI (Do Not Populate / Do Not Install)
Designation for components listed in the BOM but intentionally not assembled onto the PCB.
ENIG (Electroless Nickel Immersion Gold)
PCB surface finish providing a flat, solderable, and wire-bondable surface. Preferred for fine-pitch components and BGA packages.
Fiducial Mark
Reference mark on a PCB used by pick-and-place machines and AOI systems to establish coordinate reference for accurate component placement.
Flying Probe Test
Electrical test method using moving test probes to contact test points on an assembled PCB. No dedicated fixture required — suitable for prototypes and small batches.
Gerber File
Standard file format (RS-274X) used to describe PCB copper layers, solder mask, silkscreen, and board outline for PCB fabrication.
HASL (Hot Air Solder Leveling)
PCB surface finish where bare copper is coated with solder and leveled with hot air. Cost-effective but not suitable for fine-pitch components.
ICT (In-Circuit Test)
Electrical test method using a bed-of-nails fixture to contact all test points simultaneously, verifying component values and circuit connectivity.
IPC-A-610
Industry standard defining acceptability criteria for electronic assemblies. Class 1 (general), Class 2 (dedicated service), Class 3 (high reliability). Most PCB assembly uses Class 2.
MES (Manufacturing Execution System)
Software system that tracks and records every step of the production process, enabling full traceability from component lot to finished assembly.
MPN (Manufacturer Part Number)
Unique identifier assigned by a component manufacturer to a specific component. Essential for accurate component sourcing and BOM processing.
OSP (Organic Solderability Preservative)
PCB surface finish using an organic compound to protect copper from oxidation. Low cost, flat surface, but limited shelf life.
Paste Stencil
Thin metal sheet (typically stainless steel) with apertures matching SMT pad locations, used to apply solder paste to PCB pads before component placement.
QFN (Quad Flat No-Lead)
IC package with exposed pads on the bottom. Requires careful solder paste volume control and thermal pad via design for reliable assembly.
Reflow Soldering
SMT assembly process where solder paste is melted in a controlled temperature profile oven to form solder joints between component leads/pads and PCB pads.
SMT (Surface Mount Technology)
PCB assembly method where components are placed directly on PCB pads and soldered by reflow. Enables smaller, denser assemblies than through-hole technology.
SPI (Solder Paste Inspection)
3D inspection of solder paste deposits after stencil printing, measuring volume, area, height, and offset to detect printing defects before component placement.
THT (Through-Hole Technology)
PCB assembly method where component leads are inserted through drilled holes and soldered on the opposite side, typically by wave soldering or hand soldering.
Tombstoning
SMT defect where a component stands up on one end due to unequal solder wetting forces. Common on small passives (0402, 0201). Prevented by balanced pad design and thermal mass.
Turnkey Assembly
PCB assembly service where the manufacturer handles component procurement, PCB fabrication, and assembly. Customer provides design files only.
Via-in-Pad
PCB design technique where vias are placed within component pads. Requires vias to be filled and capped to prevent solder wicking into the via during reflow.
Wave Soldering
Through-hole soldering process where assembled PCBs pass over a wave of molten solder to form joints on the bottom side.
X-Ray Inspection
Non-destructive inspection technique using X-rays to visualize solder joints hidden under BGA and CSP packages. Detects voids, bridges, and missing balls.