In the fast-moving world of electronics, compact and modular designs are becoming the norm—especially for IoT, wireless, and embedded systems. One crucial technology enabling these compact designs is the castellated PCB. If you’ve ever worked with plug-and-play modules like Wi-Fi or Bluetooth boards, chances are you’ve already encountered a castellated PCB without realizing it. This guide will help you understand what a castellated PCB is, how it works, where it’s used, and how much it costs in 2025. Whether you’re a beginner or a product engineer, this is the only beginner’s guide you’ll need.
1. What Is a Castellated PCB?
A castellated PCB—also known as a PCB with castellated holes or half-hole PCB—is a printed circuit board that has small plated holes cut along the edges. These holes are only partially drilled, appearing as semi-circular notches when viewed from the edge.
The name “castellated” comes from the resemblance to the crenellated walls of medieval castles. These semi-holes serve as direct connection points to another board via surface mount soldering, making them ideal for daughter boards or modules.
2. How Does a Castellated PCB Work?
Castellated PCBs are designed to be mounted onto a larger “mother” PCB. The half-holes are plated with copper and aligned to match surface pads on the host board. During the assembly process, solder paste is applied to the host PCB, and the castellated module is reflow soldered into place.
This provides a solid electrical and mechanical connection—without needing through-hole pins or complex connectors. It’s a cost-effective and space-saving solution for integrating pre-certified RF, wireless, or microcontroller modules into larger systems.
3. Key Features and Benefits of Castellated PCBs
Castellated PCBs are widely adopted because of several technical and economic benefits:
- Easy integration: They allow module-to-board connection using standard SMT equipment.
- Simplified testing: Test points are exposed on the board edge, allowing for easy probe access.
- Quick prototyping: Ideal for plug-and-play designs that can be easily replaced or updated.
- Space-saving: Eliminates the need for bulky connectors in compact applications.
- Cost-effective: Lower component count and simplified assembly reduce production costs.
4. Common Applications of Castellated PCBs
Due to their modularity and ease of integration, castellated PCBs are used across a wide range of electronic products:
- Wireless communication modules (Wi-Fi, Bluetooth, Zigbee)
- GPS and GNSS receivers
- IoT sensors and controllers
- Microcontroller-based breakout boards
- RF and power amplifier modules
- Audio and video transmitter modules
Essentially, any application that requires a compact, replaceable daughter board can benefit from castellated PCB technology.
5. Castellated PCB Design Guidelines for Beginners
If you’re planning to design a castellated PCB, here are a few practical tips to ensure success:
- Hole Size and Spacing: The standard via size is typically 0.6 mm, with spacing of at least 1.2 mm between holes.
- Pad Design: Align castellated holes with corresponding SMT pads on the base PCB to ensure proper soldering.
- Copper Plating: Ensure proper copper plating within the half-holes to maintain electrical connectivity.
- Solder Mask: Avoid solder mask overlap near the castellated edges to ensure solid solder joints.
- Mechanical Support: If the module is large or heavy, consider mechanical fasteners in addition to soldering.
6. Manufacturing Process of Castellated PCBs
Producing a castellated PCB involves several specialized steps during fabrication:
- Drilling: Holes are drilled along the edges of the board.
- Plating: Copper is electroplated to coat the inside of the holes.
- Routing: The board is milled such that half of each hole is removed, creating the characteristic “castellated” edge.
- Finishing: Surface finishes like ENIG or HASL are applied, ensuring solderability and corrosion protection.
These steps require high precision. Not all PCB manufacturers offer castellated options, so choose a factory with proven experience.
7. How Much Do Castellated PCBs Cost in 2025?
The cost of castellated PCBs in 2025 depends on several factors, including board size, number of holes, layers, material type, and production volume.
- Prototype (2-layer, 50x50mm): ~$40–$70 for 5 pieces
- Medium-run (100pcs): ~$1.20–$2.00 per board
- 4-layer advanced boards: ~$3.50–$5.00 per unit in volume production
Additional costs may apply for custom tooling, impedance control, or non-standard finishes.
8. Tips for Choosing the Right Castellated PCB Supplier
Selecting the right manufacturing partner is critical. Here’s what to look for:
- Experience with castellated routing and plating
- Minimum drill-to-edge tolerance within 0.2mm
- Flexible prototyping and low MOQ
- Fast lead times with optional panelization
- Clear DFM support to prevent manufacturing delays
Suppliers like KingSunPCB specialize in high-precision castellated PCB production and offer one-on-one engineering support from prototyping to volume manufacturing.
9. Frequently Asked Questions (FAQ)
Q1: Can I design a castellated PCB with more than two layers?
Yes, castellated PCBs can be 2, 4, or even 6 layers, depending on the design requirements.
Q2: What causes poor solder joints on castellated edges?
Common causes include poor pad alignment, insufficient solder paste, or uneven board surface.
Q3: Are castellated PCBs suitable for rework or removal?
Yes, but careful heat management is required to avoid pad lifting during desoldering.
10. Conclusion: Is a Castellated PCB Right for Your Project?
If your project involves modular design, wireless integration, or rapid prototyping, a castellated PCB is a smart and scalable solution. Its compact footprint, ease of assembly, and cost efficiency make it the go-to choice for many product engineers in 2025. Partnering with an experienced PCB supplier ensures that your castellated design meets both performance and budget expectations.