PCB Industry Terminology Explained

　　 This issue introduces the fundamental part of commonly used PCB terminology. It covers terms related to materials, hole types & interconnection technology, and the manufacturing process.

Materials 
　　FR-4: The most commonly used PCB substrate material, a glass fiber reinforced epoxy resin flame-retardant laminate (FR = Flame Retardant).
　　Copper Clad Laminate (CCL): The core base material for PCB fabrication, also referred to as the core.

　　Prepreg:  A partially cured resin material, similar to “glue,” which melts during lamination and bonds the core layers together.

　　Copper Foil:  A thin layer of copper laminated onto the substrate, which is etched to form conductive traces.
　　Flexible Substrates:  Such as polyimide (PI), used in flexible printed circuits (FPC).

　　High-Performance Substrates:  Materials such as Rogers, halogen-free, and low-loss laminates, used for high-speed and high-frequency applications.

Hole Types and Interconnection Technology
　　Through-Hole: A hole drilled through the entire PCB, used for through-hole components or electrical interconnection.
　　Via: A general term for holes providing interlayer electrical connections.

　　Blind Via: Connects an outer layer to one or more inner layers, without passing through the entire board.

　　Buried Via:  Connects only internal layers, without reaching the outer layers.
　　PTH (Plated Through-Hole):  A via with copper plating on the hole wall, enabling electrical connection.

　　NPTH (Non-Plated Through-Hole): A via without copper plating, usually used for mechanical mounting or positioning.
　　Backdrill:  A process of removing unused portions of plated through-holes to improve signal integrity in high-speed designs.

Manufacturing Process
　　Cutting: Cut large sheets of copper-clad laminate into panels of the size required for production.
　　Inner Layer Imaging: Transfer the inner layer circuit pattern to the core board through processes such as exposure, development, and etching.

　　Lamination: Laminate the core board, prepreg, and copper foil into a single integral multilayer board under high temperature and high pressure.

　　Drilling:  Use CNC drilling machines to drill various through-holes and blind/buried vias on the PCB.
　　Etching:  Use chemical solutions to etch away the copper without a protective layer, leaving the final circuit pattern.

　　Solder Mask Printing: Cover the board with solder mask ink by screen printing or coating, and then expose it.
　　Surface Finish:  Applying protective coatings to exposed pads.

Surface Finish
　　HASL(Hot Air Solder Leveling): Low-cost, widely used, but with limited flatness.
　　ENIG(Electroless Nickel Immersion Gold): Excellent flatness and solderability, suitable for wire bonding, but relatively costly.

　　OSP(Organic Solderability Preservative): Environmentally friendly and low-cost, but with a short shelf life.

　　Immersion Silver/Tin:  Provides good flatness and serves as alternatives to HASL and ENIG.
　　Hard Gold Finger:  Used on connector contact areas for high wear resistance.

Inspection & Testing
　　HASL(Hot Air Solder Leveling): Detecting defects in circuit patterns.
　　AVI (Automated Vision Inspection): Inspecting PCB appearance.

　　X-Ray Inspection: Used to detect hidden joints, such as BGA solder balls.

　　Flying Probe Test:  Testing electrical connectivity using movable probes, suitable for prototypes or small batches.
　　Impedance Control:  Ensuring transmission line impedance meets design targets (e.g., 50Ω), critical for high-speed circuits.

PCB Layout & Packaging
　　Impedance Design: Including single-ended and differential impedance design.

　　Stack-Up Design: Planning PCB layer structure to meet routing, impedance, and EMC requirements.

　　BGA (Ball Grid Array)：A package type with solder balls arranged in a grid, commonly used for high I/O devices.