Detailed Explanation of Common PCB Terminology
1. Basic PCB Structure Terms
Annular Ring refers to the copper ring surrounding a plated through-hole (PTH) on a PCB. This structure is critical for component mounting and signal transmission, and its width directly affects connection reliability and current-carrying capacity. Designers must ensure sufficient annular ring width to prevent connection failures due to drilling misalignment.
Pad is an exposed metal area on the PCB surface used for soldering components. Depending on the component type, pads can be categorized as through-hole pads or surface-mount pads. Pad design must consider factors such as component size, soldering process, and current requirements.
Plane refers to large copper areas on a PCB, typically used for power or ground distribution. Unlike signal traces, planes are defined by boundaries rather than paths, offering lower impedance and better heat dissipation. Proper use of planes can significantly improve a PCB’s electromagnetic compatibility (EMC).
2. PCB Design and Verification Terms
DRC (Design Rule Check) is an automated verification feature in PCB design software that ensures compliance with manufacturing requirements. It detects common issues such as insufficient trace spacing, undersized holes, or inadequate annular rings, ensuring manufacturability.
Gerber Files are the standard file format for PCB manufacturing, containing graphical data for each layer. Modern Gerber files typically use the RS-274X format, supporting embedded aperture tables and layer attributes. Accurate Gerber file generation is crucial for transitioning from design to production.
ODB++ Files are an alternative manufacturing data format that uses a database structure instead of separate files, providing a more complete representation of design intent. Compared to Gerber, ODB++ includes additional information such as netlists and material specifications, reducing communication errors.
3. PCB Hole-Related Terms
Plated Through-Hole (PTH) is a hole drilled through the entire PCB and plated with conductive metal, used for interlayer connections or mounting through-hole components. PTH reliability depends on plating quality and thickness, typically requiring an average copper thickness of at least 20μm.
Via is a plated hole specifically for interlayer connections, categorized into three main types:
- Through Via: Passes through all layers, simple to manufacture but occupies more space.
- Blind Via: Connects an outer layer to an inner layer, increasing routing density.
- Buried Via: Connects only inner layers, further conserving surface space.
Microvia is a small via (typically less than 150μm in diameter) created using laser drilling, widely used in HDI (High-Density Interconnect) boards. Microvias enable higher connection density, supporting modern high-pin-count components.
4. PCB Manufacturing Process Terms
Solder Mask is a protective coating applied to the PCB surface, usually green (though red, blue, black, and other colors are also used). It prevents short circuits and oxidation, with openings exposing pads for soldering. Alignment accuracy directly affects soldering quality.
Solder Paste is a mixture of solder powder and flux used in surface-mount assembly. It is precisely deposited onto pads using a stencil and melts during reflow soldering to form electrical connections. The metal composition, particle size, and activity level must be selected based on application requirements.
Reflow Soldering is a critical step in SMT assembly, where controlled heating melts the solder paste to form reliable joints. A typical reflow profile includes preheating, soaking, reflow, and cooling stages, each requiring precise temperature control.
5. Special PCB Structures and Materials
Gold Finger refers to gold-plated contact tabs on the edge of a PCB, typically using hard gold plating (with a nickel underlayer) for wear resistance. Design considerations include insertion force, contact resistance, and mating cycles. Commonly found in memory modules and expansion cards.
Rigid-Flex PCB combines the benefits of rigid and flexible circuits, featuring both rigid and flexible sections. This design reduces connector requirements and improves reliability, but is more expensive and complex to design. Often used in aerospace and medical devices.
Prepreg (Pre-Impregnated Material) is a bonding material in multilayer PCBs, consisting of resin-coated fiberglass. During lamination, the resin flows and cures, bonding core layers together. Different prepreg types vary in resin content and flow characteristics.
6. PCB Assembly and Testing Terms
Pick and Place is an automated component placement process in SMT assembly lines. Modern machines achieve placement speeds of tens of thousands of components per hour with ±25μm accuracy. Programming considerations include component recognition, feeder arrangement, and placement sequence.
Wave Soldering is used for through-hole components, where the PCB passes over a molten solder wave, forming joints via capillary action. Key process controls include flux application, preheat temperature, and wave contact time.
Flying Probe Test is a fixtureless electrical testing method where programmable probes contact test points to verify continuity and insulation. Compared to bed-of-nails testing, flying probe tests require less setup time and are ideal for low-volume production.
7. Advanced PCB Design Concepts
Copper Etching removes excess copper to form circuit patterns. To reduce etching time and chemical consumption, unused copper areas are often designed as grids or hatched patterns—a technique known as copper thieving or balancing.
Thermal Relief is a special trace design connecting pads to planes, using thin spokes instead of solid connections to control heat dissipation during soldering. Proper thermal relief ensures electrical performance while facilitating soldering.
Signal Integrity (SI) studies signal transmission quality on PCBs, covering impedance control, crosstalk suppression, and timing analysis. High-speed designs must account for skin effect, dielectric loss, and via impedance discontinuities.
By mastering these PCB terms, engineers can communicate design intent more accurately, troubleshoot manufacturing issues more effectively, and collaborate better across the supply chain. As electronics technology evolves, PCB terminology continues to expand, making continuous learning essential for maintaining professional expertise.