Basic PCB Terminology List You Should Know

Introduction to Basic PCB Terminology

Understanding the terminology associated with Printed Circuit Boards (PCBs) is essential for anyone involved in electronics design, manufacturing, or assembly. Whether you are an engineer, technician, or enthusiast, having a solid grasp of PCB terminology enables effective communication and comprehension within the field. This basic PCB terminology list serves as a foundational reference to familiarize yourself with the essential terms and concepts commonly encountered in PCB-related discussions and documentation. By acquiring a working knowledge of these terms, you will be better equipped to navigate the world of PCBs and engage in meaningful discussions about design, fabrication, assembly, testing, and troubleshooting processes. Let’s explore the key PCB terminologies that form the building blocks of this exciting and dynamic field.

 PCB Base Materials

• Substrate: Base insulating material, often FR-4 fiberglass.
• Prepreg: Fiberglass sheet with resin, used in multilayer boards.
• Copper foil: Thin copper layer forming circuits.
• Core: Central substrate layer in a multilayer board.
• Resin: Epoxy polymer bonding layers together.
• Weave: Fiberglass reinforcement pattern.
• Dielectric: Insulating material between conductors; FR-4’s dielectric constant is ~4.
• Lamination: Process of bonding foil and prepreg layers using heat and pressure.
• High-frequency laminates: Materials like Rogers or Teflon for RF/microwave applications.
• Thermal conductivity: Ability of a material to conduct heat.
• CTE (Coefficient of Thermal Expansion): Material expansion/contraction with temperature.

PCB Fabrication

• CAM (Computer Aided Manufacturing): The use of computer software to aid in the conversion of design files for tooling and manufacturing processes.
• Etching: The chemical process of removing unwanted copper from a PCB, leaving only the desired copper traces and pads.
• Photoresist: A light-sensitive material applied to a PCB. When exposed to light and developed, it forms a protective barrier over areas of copper that should not be etched.
• Tenting: The process of covering vias (holes) with photoresist to protect them during etching.
• Solder mask: A protective layer, often green but available in various colors, that is applied over the PCB to prevent solder bridges and protect the copper from environmental factors.
• Silkscreen: A layer of ink markings applied to a PCB to indicate component placements, reference designators, logos, test points, and other information.
• Plating: The electrochemical process of adding a layer of metal (commonly copper) to the PCB, specifically in the drilled holes to create vias.
• Panel: A larger board containing multiple individual PCB designs. This approach is used for manufacturing efficiency. After fabrication, the panel is broken down to separate the individual PCBs.
• Lamination: The process of bonding multiple layers of material together using heat and pressure, often used in multilayer PCBs.
• PTH (Plated Through Hole): A hole in the PCB that has been electroplated to allow electrical connectivity between different layers of the board.
• OSP (Organic Solderability Preservative): A type of surface finish applied to a PCB to enhance its solderability and protect the copper from oxidation.
• HDI (High Density Interconnect): A type of PCB design and manufacturing that uses small geometries and tight tolerances to allow for more components in a smaller space.
• Microvia: A very small via, often used in HDI designs, that connects layers in a multilayer PCB.
• Impedance control: A process in PCB fabrication to ensure that certain traces have a specific impedance, important for high-frequency designs.
• HASL (Hot Air Solder Leveling): A method of applying a thin layer of solder over the copper pads on a PCB to improve solderability.
• Copper weight/thickness: The thickness of the copper layer on a PCB, typically measured in ounces per square foot.
• Surface finish: The final protective and solderable layer applied to exposed copper pads on a PCB. Examples include OSP, HASL, ENIG (Electroless Nickel Immersion Gold), and more.
• Buried via: A via that connects internal layers of a multilayer PCB and doesn’t reach the outer layers.
• Blind via: A via that starts on an external layer but stops on an internal layer, not passing through the entire board.
• Gerber file: A standard file format that contains information about a PCB’s design, used by manufacturers to produce the board.
• Annular Ring: The area of copper pad that surrounds a drilled hole in a PCB.
• Backdrilling: The process of removing the unused portion of a plated through-hole to reduce parasitic capacitance.
• Bare Board: A PCB that has been fabricated but has no components assembled onto it.
• Breakaway Tab: Small tabs that hold individual PCBs together within a larger panel, which are later broken away.
• Copper Thieving: Copper patterns added to the outer layers of a PCB to help ensure an even plate across the board during fabrication.
• Electroless Copper: A thin layer of copper deposited chemically without electricity, often used as a precursor to electroplating additional copper.
• ENIG (Electroless Nickel Immersion Gold): A type of surface finish used on PCBs, consisting of an underlying layer of nickel with a thin coating of gold on top.
• Epoxy Resin: A type of polymer used to bond the layers of a multilayer PCB.
• Flash Gold: A very thin layer of gold plated over nickel, used primarily for protection and not for soldering.
• Inner Layer: Layers inside a multilayer PCB, which are not visible from the outside.
• Legend: Another term for silkscreen, the printed labels and markings on a PCB.
• NPTH (Non-Plated Through Hole): Holes in a PCB that are not plated with copper, often used for mounting or mechanical purposes.
• Pad: A piece of conductive material on a PCB where a component is attached using solder.
• Peelable Mask: A temporary solder mask that can be peeled away after soldering.
• Reference Marker: A mark on a PCB, often a “+” sign, used for alignment during the assembly process.
• Scoring: A method of creating weak lines on a panel of PCBs, allowing them to be easily broken apart after fabrication.
• SMOBC (Solder Mask Over Bare Copper): A process where solder mask is applied directly over bare copper, and then the exposed copper pads are plated.
• Step and Repeat: A process where a single PCB design is duplicated multiple times on a larger panel to optimize manufacturing.
• Test Coupon: A small section added to a PCB panel containing test structures, used to verify the fabrication process.

PCB Assembly

• Conformal Coating：A protective coating applied to a printed circuit board to prevent damage from moisture, dust, chemicals and temperature extremes.
• SMT (Surface Mount Technology): Components are soldered directly to the surface of PCB pads rather than through holes. This technique improves component density and allows for a more compact PCB layout.
• Reflow Soldering: The process of soldering SMT components by heating the entire PCB assembly in a convective oven. This melts the solder paste, solidifying the connection between components and the PCB.
• Wave Soldering: A method of soldering leaded through-hole components by passing the PCB over a wave of molten solder.
• Hand Assembly: Manual technique involving soldering and mounting components. It’s primarily used for small batches, rework, and repairs.
• Pick and Place: An automated machine that picks up components and places them with precision onto the PCBs before soldering.
• Screen Printing: A process using a stencil to apply solder paste to the PCB, allowing solder to be placed precisely where components will be mounted.
• AOI (Automated Optical Inspection): A visual inspection method that uses automated machines to scan the assembled PCB for defects.
• J-STD-001: A joint industry standard that describes the materials, methods, and verification criteria for producing high-quality soldered interconnections.
• BGA (Ball Grid Array): A type of surface mount package for integrated circuits. It uses solder balls on the bottom as its connectors.
• QFN (Quad Flat No-leads): Another type of surface mount package for integrated circuits, characterized by having terminals on the bottom but no protruding leads.
• Underfill: A protective epoxy applied between BGAs or other chips and the PCB. It helps to reinforce solder joints and protect against mechanical stress.
• X-Ray Inspection: A non-destructive testing method using X-ray imaging to inspect internal solder joints, especially useful for BGAs and other hidden connections.
• Thru-Hole Components: Components that come with leads designed to be soldered into plated through-holes in the PCB.
• ECO (Engineering Change Order): An official document indicating a modification to the PCB design or the bill of materials. It’s used when changes are needed after the initial design phase.
• Depaneling: The process of separating individual PCBs from larger panels after the assembly process. This is typically done when multiple PCBs are fabricated on a single panel for manufacturing efficiency.

PCB Parameters

• Layers: Number of copper layers.
• Thickness: Total thickness of the board.
• Aspect ratio: Ratio of thickness to minimum trace/space width.
• Pitch: Spacing between pins or traces.
• Track/Trace: Conducting copper circuit.
• Space: Gap between adjacent traces.
• Line width: Width of a trace.
• Annular ring: Copper pad area around a hole.
• Finished hole size: Diameter of drilled hole after plating.
• Tolerance: Allowable variation in parameters.
• Clearance: Distance between copper features on the same layer.
• Mask expansion: Pullback of solder mask from copper edge.
• Stackup: Arrangement of layers in a multilayer PCB.
• Ground pour: Connecting isolated areas to ground to reduce EMI.
• Guard trace: Grounded trace between two signal traces to prevent crosstalk.

PCB Testing & Quality

• ICT (In-Circuit Test): A method of testing wherein a machine checks the populated PCB, looking for shorts, opens, resistances, capacitances, and other basic quantities to ensure correct assembly.
• Flying Probe Test: A type of ICT that doesn’t require a test fixture. Movable probes are used to quickly test PCBs without the need for a dedicated bed-of-nails test fixture.
• Functional Test: After ICT, the PCB undergoes a functional test to mimic the final electrical environment and ensure it performs its intended function.
• AOI (Automated Optical Inspection): A visual inspection method where a machine scans the assembled PCB for component and soldering defects.
• X-ray Inspection: Non-destructive testing to inspect solder joints under BGAs or other components where the soldering isn’t visible to the naked eye.
• Boundary Scan (JTAG): A testing method that checks solder connections and verifies the functionality of some components.
• Burn-in Test: Boards are powered and subjected to thermal stress to identify early failures.
• Environmental Stress Test: Exposing the PCB to a range of environmental conditions to ensure functionality across temperatures, humidities, and other environmental factors.
• Thermal Cycling: Testing the PCB’s response to temperature changes to identify potential solder joint failures.
• Vibration and Shock Test: Simulates the mechanical stresses a PCB might face during its life to ensure reliability.
• Golden Board: A reference board known to be defect-free against which manufactured PCBs are compared.
• DFT (Design For Testability): Designing a PCB in a way that makes it easier to test, ensuring more accurate results and efficient troubleshooting.
• FCT (Functional Circuit Test): A test that checks if the PCB functions as intended, often including firmware and software interactions.
• Coverage Analysis: Evaluating how much of a PCB’s circuitry is tested by the current testing methods.
• FA (Failure Analysis): In case of a test failure, FA is conducted to understand the root cause of the failure.
• Yield Analysis: Measures the ratio of good boards produced to the total boards manufactured. A crucial metric for assessing manufacturing effectiveness and quality.
• Process Capability (Cpk): A statistical measure to assess if a process can produce an output within specification limits.
• DPPM (Defects Per Million): A metric that quantifies the defect rate of a manufacturing process.
• RoHS Compliance Testing: Ensures that the PCB assembly adheres to the Restriction of Hazardous Substances Directive, which limits the use of specific hazardous materials.
• Continuity and Isolation Testing: Ensures that electrical connections are complete and that there are no unintended connections.

PCB Repairs & Modifications

• Re-spin: The process of updating and producing a new version of a PCB layout to correct issues identified in a previous version.
• Errata: Documented known issues or mistakes on a PCB. It provides workarounds or corrections for users and manufacturers.
• Jumpers: Temporary solutions using wires to connect two points on a PCB, often used to bypass a broken trace or correct a design error.
• Rework: The process of correcting defects on already assembled PCBs. This can involve component replacement, soldering, and other tasks.
• Hot Air Rework: Using a hot air gun to desolder and replace faulty SMT components without damaging neighboring components.
• BGA Rework Station: Specialized equipment for removing and replacing Ball Grid Array (BGA) packages, which require precise alignment and heat control.
• Hand Soldering: Manual soldering technique used for component replacement, adding jumpers, or fixing solder bridges.
• Desoldering: The process of removing solder from a joint, often using tools like solder wick, desoldering pumps, or hot air.
• Pad Repair: Fixing lifted or damaged pads on a PCB, often using epoxy and copper foil.
• Trace Repair: Restoring a damaged or broken trace using conductive ink, copper tape, or jumper wires.
• Conformal Coating Rework: Removing and reapplying a protective coating from a PCB section to facilitate repairs.
• Editing: The act of modifying a PCB by cutting traces, adding jumper wires, or making other physical changes to correct design errors or enhance functionality.
• Underfill Removal: Removing the epoxy from beneath a component (like a BGA) to facilitate its removal and replacement.
• Reballing: The process of replacing the solder balls on the underside of a BGA or other ball grid package.
• Thermal Profiling: Adjusting the thermal profile of soldering equipment to match the specific requirements of a PCB, ensuring proper solder flow and component adhesion during rework.
• Focused IR (Infrared): Using infrared heaters to localize heat to a specific area of a PCB, allowing for targeted component removal without affecting the entire board.
• Epoxy Curing: Using heat or UV light to harden applied epoxy, often used during pad or trace repairs.
• Component Harvesting: Removing usable components from a defective board for reuse or testing.
• PCB Cleaning: Removing flux residues, contaminants, or debris after repair processes using solvents or ultrasonic cleaners.
• Inspection: Using magnification, AOI, or X-ray techniques to ensure the quality of repair and modification work.

Conclusion

In conclusion, the terminology related to PCBs encompasses various aspects of electrical design, fabrication, assembly, testing, quality control, and reliability. As you delve deeper into the field of PCB engineering, these terms will become more familiar to you. This glossary can serve as a valuable resource to refresh your memory and reinforce your understanding of key PCB vocabulary. By expanding your knowledge of PCB terminology, you will be better equipped to navigate the complexities of PCB engineering and contribute to the development of innovative electronic systems.

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