PCB Glossary
Plain-English definitions of the HDI and high-difficulty PCB terms we use across the site. Each term links to the capability it relates to.
- Annular ring
- The ring of copper around a drilled hole's pad; a larger ring improves reliability. Learn more →
- Any-layer HDI
- An HDI build where every layer can carry microvias, so any layer connects to its neighbor — the highest interconnect density. Learn more →
- Aspect ratio
- Board thickness divided by hole diameter (or microvia depth / diameter); higher ratios are harder to plate reliably. Learn more →
- Backplane
- A thick, high-layer-count board that interconnects other boards via connectors. Learn more →
- Blind via
- A via connecting an outer layer to an inner layer without passing through the whole board. Learn more →
- Buried via
- A via between inner layers only, not reaching either surface. Learn more →
- Build-up (1+N+1, 2+N+2)
- Notation for HDI microvia layers on each side of an N-layer core; "any-layer" means every layer is a build-up layer. Learn more →
- Controlled impedance
- Designing trace width and dielectric height to hit a target impedance (e.g., 50 ohm) for clean signals. Learn more →
- Coverlay
- A flexible polyimide film that protects the conductors on a flex circuit. Learn more →
- CTE (coefficient of thermal expansion)
- How much a material expands with heat; low CTE improves dimensional stability and reliability. Learn more →
- Dk / Df
- Dielectric constant (Dk) and loss tangent (Df); low values preserve high-speed and RF signal integrity. Learn more →
- ENIG / ENEPIG
- Electroless nickel immersion gold (and with palladium); flat, solderable surface finishes for fine-pitch parts. Learn more →
- Heavy copper
- Copper weights of roughly 3 oz and above for high-current power boards. Learn more →
- HDI (High Density Interconnect)
- A PCB technology using laser-drilled microvias for far higher routing density than conventional boards. Learn more →
- IPC Class 3
- The high-reliability acceptance level in IPC standards, used in aerospace, medical and defense. Learn more →
- Laser microvia
- A small, laser-drilled via connecting adjacent layers; advanced processes reach 0.07 mm. Learn more →
- Layer count
- The number of conductive layers in a board; high layer counts demand tight registration. Learn more →
- Line / space
- The minimum trace width and gap between traces a fabricator can produce. Learn more →
- Low-loss laminate
- Materials (e.g., Megtron 6/7) with low Df for multi-gigabit signals. Learn more →
- Megtron 6 / 7
- Panasonic low-loss laminates widely used for high-speed digital designs. Learn more →
- Metal core (MCPCB)
- A board with an aluminum or copper core for thermal management. Learn more →
- Mixed-dielectric (hybrid) stackup
- A stackup combining different dielectric materials (e.g., Rogers + FR-4) in one board. Learn more →
- No-flow PP
- Prepreg formulated to limit resin flow, used at flex-to-rigid transitions in rigid-flex. Learn more →
- Adhesiveless PI
- Polyimide flex base without an adhesive layer; better hole-wall quality and bend reliability. Learn more →
- Rigid-flex
- A board combining rigid sections and flexible sections in one structure. Learn more →
- Rogers / PTFE
- Low-loss RF laminates for microwave and high-frequency designs. Learn more →
- Sequential lamination
- Building a board in multiple lamination cycles to form blind/buried vias and HDI build-ups. Learn more →
- Stacked vs staggered microvia
- Stacked microvias sit directly on each other (densest, needs copper fill); staggered are offset (more robust). Learn more →
- Tg (glass transition temperature)
- The temperature where a laminate softens; higher Tg improves processability and reliability. Learn more →
- Via-in-pad
- A microvia placed inside a component pad (filled and capped flat) for fine-pitch BGAs. Learn more →