Castellated PCB: What Are Castellated Holes, Pads, and Board Edge Connections?

Sep 22,2026

What Is a Castellated PCB?

A castellated PCB is a circuit board with plated holes located directly along its edge. During PCB profiling, the board is cut through these holes, leaving exposed, plated half-holes along the edge.

These exposed half-holes, also called castellated holes or plated half-holes, act as solderable connection points. A small module PCB can then be soldered directly to matching pads on a larger carrier board.

The result is a compact PCB-to-PCB connection without requiring a separate connector for the module-to-carrier connection.

How Do Castellated Holes Work?

A castellated hole starts as a plated hole positioned at the PCB edge. The board outline is then routed through the hole so that part of the plated barrel remains exposed along the finished edge.
The remaining plated section provides a conductive surface that can be soldered to a corresponding pad on another PCB.

A typical connection consists of:

A module PCB with castellated holes along its edge
Matching pads on the carrier PCB
Solder applied to the carrier-board pads
The module positioned against the carrier PCB
Reflow or another appropriate soldering process forming the electrical and mechanical connection

This approach allows the module to be assembled onto the main PCB as part of the overall electronic assembly.

What Are Castellated Pads?

Castellated pads are the exposed solderable areas created when plated holes are cut at the PCB edge.

The terms castellated holes, plated half-holes, and castellated edges are often used to describe this type of PCB feature. The important characteristic is that the plated hole is positioned at the board outline so that part of its conductive surface remains exposed after profiling.

These exposed areas provide the interface between the module and the carrier board.

Castellated PCB vs. Standard Board-to-Board Connections

Castellated connections are one option for connecting two PCBs. Whether they are appropriate depends on the mechanical and electrical requirements of the product.

Feature	Castellated PCB Connection	Separate Board-to-Board Connector
Connection method	Soldered directly between PCBs	Mating connector contacts
Additional connector	Not necessarily required	Required
Assembly	Module is soldered to carrier PCB	Connector and mating board are assembled
Removability	Generally not intended for routine removal	Can support removable connections depending on connector
Space requirements	Uses the PCB edge and carrier footprint	Requires connector components and mating space
Common use	Embedded modules and compact PCB assemblies	Applications requiring a detachable connection

A castellated connection is particularly useful when a module is intended to become a permanent part of the final assembly.

Castellated PCB Design Considerations

A castellated PCB should be designed with both PCB fabrication and final assembly in mind.

1. Hole and Pad Geometry
The hole diameter, pad dimensions, spacing, and position relative to the board outline need to be compatible with the PCB manufacturer's capabilities and the intended assembly process.
There is no single hole size or spacing that applies to every castellated design. Requirements depend on the board construction, fabrication process, PCB assembly method, and manufacturer's capabilities.

2. Board Outline
The board outline must intersect the plated holes correctly so the required portion of each hole remains exposed after profiling.
The relationship between the hole location and the final board edge is therefore an important part of the design.

3. Plating
Because the exposed hole wall forms part of the solderable connection, the plating process needs to provide a suitable conductive surface.

4. Carrier-Board Footprint
The module and carrier PCB should be designed together. The carrier-board pads need to align with the castellated features and provide an appropriate soldering area.

5. Mechanical Alignment
The module outline, castellated-hole positions, and carrier-board footprint should be checked for alignment before fabrication and assembly.

How Are Castellated Holes Manufactured?

The exact manufacturing sequence can vary, but a common approach begins with plated through-holes positioned at the PCB edge.

The holes are drilled and plated, and the board is subsequently profiled so that the final edge cuts through the holes. This leaves the exposed plated half-holes that form the castellated edge.

The profiling operation needs to be controlled carefully because the edge is part of the electrical connection. Excessive damage, burrs, or other edge defects can affect the finished castellated feature.

For this reason, castellated holes should be treated as a specific fabrication requirement rather than simply as ordinary through-holes located near the board edge.

Castellated PCB Assembly Considerations

The carrier PCB and module should be considered together before assembly.

The carrier-board footprint must match the castellated edge, and the soldering process must provide sufficient solder contact for the intended connection.

After assembly, inspection should verify the alignment and solder joints along the module edge. The exposed nature of castellated connections can make visual inspection of the soldered interface practical.

The appropriate assembly method depends on the module design, solder paste application, component placement, board geometry, and production process.

Does a Castellated PCB Need a Socket?

No. A castellated PCB does not automatically require a socket.

In many applications, the module is soldered directly to the carrier PCB through its castellated holes.

A castellated PCB socket or other socket-based interface may be considered when the module needs to be removable or replaceable. The choice depends on the product's mechanical requirements and whether the module is intended to be permanently assembled.

For a permanent module-to-board connection, direct soldering may be the intended approach.

How to Choose a Castellated PCB for Your Project

Before selecting a castellated PCB design, consider:

Module size: Is the available board space suitable for an edge connection?
Connection type: Should the module be permanently soldered or removable?
Hole and pad geometry: Can the required features be manufactured consistently?
Carrier-board design: Are the matching pads correctly positioned?
Assembly process: Can the module and carrier PCB be assembled using the planned process?
Mechanical requirements: Will the soldered connection provide the required mechanical support?
Inspection: Can the finished connection be inspected effectively?
Manufacturing requirements: Does the PCB fabricator have experience with castellated or plated half-hole features?

Discussing these requirements with the PCB manufacturer before fabrication can help prevent problems caused by incompatible edge geometry or assembly requirements.

Benefits of Castellated PCB Connections

Compact PCB-to-PCB Integration: Castellated edges allow a module to be mounted directly onto a carrier PCB without adding a separate connector interface.
Simplified Module Integration: A preassembled module can be integrated into a larger PCB assembly through soldered edge connections.
Useful for Compact Designs: Because the connection is formed at the board edge, castellations can be useful when the product has limited space for conventional connectors.
Suitable for Module-Based Designs: Wireless, sensor, controller, and other electronic modules can use castellated connections to integrate with a host PCB.
Visible Solder Connection: The exposed edge of a castellated hole allows the solder joint to be inspected from the side, which can be useful during assembly inspection.

Castellated PCB Applications

Castellated PCBs are commonly used where a smaller circuit board needs to function as a module within a larger electronic assembly.

Wireless Modules: Wi-Fi, Bluetooth, and other communication modules can use castellated edges to connect directly to a host PCB.
Sensor Modules: A sensor PCB can be designed as a separate module and soldered onto a carrier board using castellated connections.
Embedded Controller Modules: A preassembled controller board can be integrated into a larger system without adding a separate connector between the two PCBs.
RF and Communication Electronics: Castellated connections are also used in compact RF and communication modules where board-to-board integration is part of the product architecture.
Development and Evaluation Boards: Castellated edges can be useful for module designs that need to be mounted onto a larger development or evaluation PCB.

Why Choose Sierra Assembly?

Sierra Assembly supports PCB manufacturing and assembly for prototype, low-volume, and production requirements.

With more than 30 years of experience, our team provides U.S.-based engineering support and works with customers to review PCB manufacturing and assembly requirements.
Sierra Assembly supports quality-focused production with ISO 9001:2015 and AS9100D certifications, along with inspection and assembly capabilities.

If your project requires a castellated PCB or another PCB-to-PCB connection method, Sierra Assembly can review your design requirements and help determine an appropriate manufacturing and assembly approach.

Frequently Asked Questions

1. Are castellated holes plated?
Ans: Yes. Castellated holes are typically based on plated through-holes, with the board profile exposing part of the plated hole at the PCB edge.

2. Can a castellated PCB be soldered directly to another PCB?
Ans: Yes. A castellated module can be soldered directly to matching pads on a carrier PCB, making it suitable for PCB-to-PCB module integration.

3. Are castellated holes the same as vias?
Ans: No. A conventional via is primarily used to provide an electrical connection between PCB layers. A castellated hole is positioned at the board edge so its plated portion becomes an exposed solderable connection.

4. Can castellated PCBs be used without a connector?
Ans: Yes. One of the main uses of castellated edges is to allow a module to be soldered directly to a carrier PCB without a separate board-to-board connector.

5. What are the main design considerations for a castellated PCB?
Ans: Key considerations include the castellated-hole geometry, board-edge position, plating, carrier-board footprint, mechanical alignment, and the planned assembly process. These features should be reviewed together to ensure the module and carrier PCB are compatible for fabrication and assembly.

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