Castellated Hole PCB, the Preferred Circuit Board Solution for Connector & RF Modules

Driven by the trend toward miniaturization of connectors, RF modules and IoT modules, castellated hole PCBs (also known as castellated edge boards in the industry) are seeing rapid adoption in precision electronics. This special PCB technology features convenient soldering, space-saving design and reliable connectivity. It is widely used in Bluetooth modules, power modules, RF adapter boards and other products.

According to PCB manufacturers, a castellated hole PCB refers to a PCB with metallized half-holes on its edge. A complete metallized hole is milled into half during profiling, forming semicircular gold-plated pads along the board edge. The inner wall copper of the castellated hole remains fully plated to maintain good conductivity. The board can be directly soldered onto the main board without additional connectors.

1. Simplified structure and reduced module size Traditional modules rely on pin headers or connectors for board-to-board interconnection. Castellated hole PCBs create soldering terminals directly on the board edge, eliminating external connectors and greatly shrinking the overall module footprint for compact product designs.
2. Reliable soldering and excellent shock resistance The inner wall of the castellated hole is fully metallized. Solder can wrap around the side wall of the half-hole to form a 3D solder joint. Compared with conventional edge pads, such joints have stronger adhesion and better resistance to vibration and drop impact, suitable for automotive and industrial control applications.
3. Lower material and assembly costs It removes connector procurement and manual pin insertion steps, simplifying the BOM. SMT mounting can complete soldering in one pass and improve production efficiency.
4. Convenient module testing and replacement A castellated-hole sub-board can be fully tested before being soldered to the main controller board. During maintenance, only the faulty module needs replacement instead of the entire main unit.

• The hole diameter and distance from the hole center to the board edge have process limits. Undersized parameters may lead to copper tearing or copper peeling.
• Avoid placing castellated holes at sharp board corners; copper layers tend to crack and peel off during profiling.
• ENIG surface finish is recommended for superior soldering reliability and oxidation resistance.
• Castellated holes are a special profiling process. Lead time is slightly longer than standard PCBs. Confirm manufacturability with your PCB manufacturer at an early design stage.

Castellated hole PCBs are widely adopted in wireless communication modules, RF transition boards, power management modules, sensor modules, industrial acquisition boards and compact automotive electronic assemblies. In high-frequency RF applications, castellated hole designs are often paired with Rogers high-frequency laminates for signal transceiver modules.

Industry insiders state that demand for miniaturized and modular electronic devices keeps rising. The castellated hole PCB process will continue to evolve and gain further penetration in AIoT and automotive electronics.

The Bluetooth communication module PCB adopts castellated hole technology for interconnection with the main motherboard.

1. Connection principle Metallized castellated holes are designed on the edge of the Bluetooth sub-board. During PCB routing profiling, half of the metallized via is milled away to form semicircular pads with intact copper on side walls. In the SMT assembly process, the Bluetooth module is mounted directly onto the corresponding pads of the main board. Solder wets and wraps the side walls of castellated holes to form 3D solder joints, which provides electrical conduction and mechanical fixation. No additional pin headers or connectors are required.
2. Key process parameters

• Castellated hole diameter: 0.8 mm,  minimum achievable size: 0.4mm
• Distance from hole center to board edge: 0.4 mm (1/2 of hole diameter)
• Copper thickness in hole: ≥20 μm
• Surface finish: ENIG, Ni:3~5μm, Au:0.05~0.1μm
• Minimum pitch between castellated holes: 1.2 mm
• Base material: FR-4, board thickness: 0.6 mm,maximum achievable thickness: 3mm
• Profiling: CNC routing for castellation; micro-etching after routing to remove burrs and prevent copper tearing
• Reliability: Solder joints pass vibration & drop test, suitable for smart switches and IoT devices.