What Are Plated Half Holes in PCB Design?

Plated half holes, also known as castellated holes, are semi-circular plated through-holes cut along the edge of a PCB. These specialized features enable secure board-to-board connections or module mounting by allowing solder bridging between adjacent PCBs. At FanyPCB, we manufacture precision castellated holes for reliable edge connections in compact electronics, IoT devices, and modular systems.

Applications of Castellated Holes

1. Module Stacking: Connect daughterboards to mainboards without connectors

2. Edge Mounting: Create solderable edges for secure mechanical attachment

3. Space-Constrained Designs: Replace bulky headers in compact devices

4. Test Points: Provide accessible measurement points along board edges

Manufacturing Process for Plated Half Holes

The production of plated half holes requires specialized PCB fabrication techniques to ensure reliable edge connections. The process begins with standard through-hole drilling at precise locations along the intended board edge, typically using mechanical drills for holes above 0.3mm or laser drilling for smaller diameters. These holes then undergo the same electroplating process as regular vias, building up a copper layer of at least 25μm to ensure proper conductivity. The critical step comes when high-precision routing equipment cuts the board edge directly through the center of these plated holes, creating the characteristic half-circle profile. This cutting process demands exceptional accuracy - even minor deviations can compromise the plating integrity. Finally, the boards receive their surface finish (such as ENIG or HASL), with particular attention paid to the exposed half-hole edges to ensure proper solderability. Throughout production, automated optical inspection verifies plating continuity and edge quality, while cross-section testing may be performed on sample boards to validate the plating thickness at the cut interface.

Essential Design Rules for Castellated Holes

Designing effective castellated holes requires careful attention to several key parameters. The hole diameter typically ranges between 0.6mm and 1.2mm - large enough for reliable soldering yet small enough to maintain board edge strength. Designers must maintain at least 0.3mm clearance between the hole cut line and any internal copper layers to prevent potential short circuits. Spacing between adjacent castellated holes should be no less than 1.5 times the hole diameter center-to-center to avoid solder bridging during assembly. The plating thickness deserves special consideration, with a minimum of 25μm copper recommended to withstand the cutting process and maintain conductivity. Board thickness also plays a role - while castellated holes can be produced on boards up to 2.4mm thick, thinner boards (1.0-1.6mm) generally yield cleaner cuts with better plating integrity. Additional design enhancements like teardrop-shaped pads can significantly improve mechanical strength, particularly for applications subject to vibration or thermal cycling. These parameters collectively ensure reliable performance while maintaining manufacturability across different PCB applications.

Benefits of Using Castellated Holes

Castellated holes offer significant advantages for modern PCB designs, particularly in space-constrained applications. Their primary benefit lies in enabling direct board-to-board connections without requiring additional connectors, which dramatically reduces both component count and overall assembly height. This proves invaluable for compact electronics like IoT devices and wearables where every millimeter matters. The plated half-hole design creates robust solder joints that are more reliable than press-fit connections, especially in environments with vibration or thermal cycling. Designers also appreciate how castellated holes simplify modular designs, allowing subsystems to be pre-tested before final assembly while maintaining excellent signal integrity across connections.

From a manufacturing perspective, castellated holes provide cost-effective solutions for several production challenges. They eliminate the need for expensive board-to-board connectors while reducing inventory complexity through standardized edge connections. The soldering process for castellated holes can often be completed in a single reflow pass alongside other SMT components, streamlining assembly workflows. This feature makes them particularly attractive for medium-to-high volume production where minimizing assembly steps translates directly to cost savings. Furthermore, the mechanical stability of properly designed castellated holes often exceeds that of connector-based solutions, reducing field failures and warranty claims in end products. These combined benefits explain why castellated holes have become a go-to solution for engineers designing reliable, space-efficient electronic systems.