Castellated Holes

What Are Castellated Holes?

Castellated holes (also called castellated vias or castle pads) are plated through-hole vias that are cut in half along the edge of a PCB, creating a row of half-cylindrical copper-plated surfaces along the board perimeter. These castellation features allow the PCB to function as a surface-mount module — the half-vias are soldered directly onto matching pads on a carrier or host board, creating electrical connections without the need for headers, connectors, or soldered wires. Castellated modules are widely used for wireless modules (WiFi, Bluetooth, cellular), sensor modules, and any subsystem designed to be easily integrated onto a larger product board.

Manufacturing castellated holes requires precise routing along the via centerlines at the board edge, followed by plating to ensure complete copper coverage on the exposed half-barrel. The quality of the castellation depends on the fabricator's routing accuracy and plating process — poor castellation can result in rough edges, incomplete plating, or copper peeling that makes the module unreliable or difficult to solder. Design guidelines for castellation include minimum hole sizes (typically 0.6mm to 1.0mm), adequate spacing between adjacent castellations, and sufficient copper connection from the half-via to the internal circuit.

Module Interface Design

Castellated hole design is critical for any PCB intended to function as a reusable module. AI-powered layout tools can ensure that castellation features are properly sized, spaced, and connected to internal circuitry according to the target manufacturing process, and that the module's host board footprint matches the castellation pattern exactly. This automated precision in module interface design prevents the mismatches between module and carrier board that are a common source of integration failures in modular electronic designs.

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