Ultimate Guide to Plated Half-Holes (Castellated Holes) in PCB Manufacturing

Table of Contents

• What Are Plated Half-Holes (Castellated Holes)?
• Primary Applications and Industry Use Cases
• Key Engineering Benefits of Castellated Edges
• Advanced: Thermal Path and Heat Dissipation
• The Manufacturing Process: Why It Requires Advanced Engineering
• DFM Guidelines: Annular Rings and Design Specifications
• Panelization Strategy: Protecting Half-Holes During Depaneling
• Quality Control, ENIG Finish, and Defect Prevention
• Why Choose NextPCB for Castellated PCB Manufacturing?
• Frequently Asked Questions (FAQs)

What Are Plated Half-Holes (Castellated Holes)?

Plated half-holes, commonly referred to in the engineering community as castellated holes, side plating, or edge plating, are plated through-holes (PTH) located directly on the boundary (outline) of a printed circuit board. During the final routing stage of PCB manufacturing, these holes are intentionally bisected. The resulting edge of the PCB resembles a series of half-cylinders lined with copper plating, looking much like the battlements of a medieval castle.

By transforming the edge of a board into a robust connection interface, castellated holes allow one printed circuit board to be mounted directly flush onto another larger motherboard. This board-on-board connection technique has become increasingly vital as hardware designs shrink and modular architectures dominate modern electronics.

Primary Applications and Industry Use Cases

As we navigate through the hardware trends of 2026, modularization is at its peak. Hardware developers prefer designing standardized sub-modules that can be attached to various mainboards. Plated half-holes are the cornerstone of this design philosophy.

• Wireless Communication Modules: Wi-Fi, Bluetooth (BLE), and LoRa modules utilize PCB module soldering techniques to act as SMD components.
• High-Frequency and RF Modules: PTFE or ceramic-based modules are mounted onto standard, low cost PCB mainboards to optimize budgets.
• Automotive and Industrial Control: Vibration-resistant sub-assemblies where mechanical connectors might fail over time.

Key Engineering Benefits of Castellated Edges

1. Profile Reduction: Eliminates Z-axis height by removing physical connectors.
2. Superior Solder Joint Reliability: Concave shapes create strong solder fillets via capillary action.
3. Environmental Protection: Zero air gap between boards prevents dust and moisture ingress.
4. Interconnection Efficiency: Low cost PCB interconnection strategy at scale by reducing BOM items.

Advanced: Thermal Path and Heat Dissipation

Beyond electrical connectivity, plated half-holes serve a critical role in thermal management for high-power modules. In modern high-current DC-DC converters or LED driver modules, the half-holes act as a direct thermal path to the motherboard's ground planes. Because the copper barrel of the half-hole is soldered directly to a large landing pad on the carrier board, it creates a low-resistance conduit for heat transfer. This auxiliary cooling mechanism helps maintain lower junction temperatures for power ICs mounted on the daughterboard.

The Manufacturing Process: Why It Requires Advanced Engineering

Standard routing will destroy a plated half-hole. To produce clean, reliable results, NextPCB utilizes a specialized workflow: Primary Drilling → Copper Plating → Specialized Edge Routing → Chemical Deburring. This ensures no copper shards remain, preventing shorts during the PCBA stage.

DFM Guidelines: Annular Rings and Design Specifications

Properly defining castellated holes in your Gerber files is critical. To ensure structural integrity and prevent copper delamination during fabrication:

• Minimum Annular Ring: To prevent the copper shell from peeling away during mechanical routing, we recommend a minimum annular ring width of 0.15 mm. This provides sufficient "meat" for the copper to bond to the substrate.
• Outline Placement: The Board Outline must cut precisely through the center of the 0.5 mm (min) drilled hole.
• Pad Design: Top and bottom copper pads (GTL/GBL) should extend at least 0.25 mm inward from the hole edge for maximum anchoring.

Panelization Strategy: Protecting Half-Holes During Depaneling

In volume production, panelization is key. However, half-holes are fragile. At NextPCB, we recommend using Tie-bars (connection joints) strategically placed away from the castellated areas. If a module is surrounded by half-holes on all four sides, use a "bridge" or "post" design on the corners. This prevents the depaneling force (V-scoring or Tab-routing) from stressing the copper plating in the holes, ensuring that the sidewalls remain intact and burr-free for assembly.

Quality Control, ENIG Finish, and Defect Prevention

The ENIG Advantage: For castellated boards, ENIG (Electroless Nickel Immersion Gold) is the gold standard. Unlike HASL, ENIG provides:

• Perfect Coplanarity: Flat pads ensure the module doesn't "tilt" during reflow.
• Sidewall Protection: ENIG coats the vertical copper barrel within the half-hole, preventing oxidation during storage. This is vital for ensuring solder wetting (intermetallic bond) during the final PCBA process.

Why Choose NextPCB for Castellated PCB Manufacturing?

NextPCB utilizes optimized routing vectors and strict quality control checks to eliminate copper peeling. We offer comprehensive turnkey PCB assembly solutions that consider the unique soldering requirements of castellated modules.

Frequently Asked Questions (FAQs)

What is the difference between a castellated hole and edge plating?

Castellated holes are individual bisected holes used for pad-to-pad soldering. Edge plating (or side plating) involves plating the entire length of a board's edge for EMI shielding or grounding. While they share similar manufacturing techniques, castellated holes are functional signal/power interconnects.

Can plated half-holes handle high current?

Yes. By increasing the number of half-holes and ensuring a robust annular ring, they can handle significant current. They also act as a thermal path to dissipate heat from high-power components.

Why is ENIG recommended over HASL for these boards?

ENIG provides a flat surface and prevents the sidewalls of the half-hole from oxidizing. HASL can result in uneven solder thickness, leading to "tombstoning" or poor alignment during the PCB module soldering process.

How do I protect half-holes during panel breakout?

Use Tie-bars or connection tabs placed at the corners of the board, rather than directly on the edges with the half-holes. This ensures the routing/snapping forces do not damage the delicate copper plating within the holes.

About the Author

Stacy Lu

With extensive experience in the PCB and PCBA industry, Stacy has established herself as a professional and dedicated Key Account Manager with an outstanding reputation. She excels at deeply understanding client needs, delivering effective and high-quality communication. Renowned for her meticulousness and reliability, Stacy is skilled at resolving client issues and fully supporting their business objectives.

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