How do you make castellated PCB?

What is a castellated PCB?

A castellated PCB, also known as a castellated hole PCB or castellated edge PCB, is a printed circuit board that features small, semi-circular holes or slots along its edges. These castellations resemble the battlements of a castle, hence the name “castellated.” The primary purpose of these castellations is to facilitate easy and secure connections between multiple PCBs or to mount the PCB onto another surface.

Castellated PCBs offer several advantages over traditional PCB designs:

  1. Simplified assembly: Castellations allow for easy alignment and soldering of multiple PCBs, reducing assembly time and complexity.
  2. Improved mechanical stability: The castellated edges provide a stronger mechanical connection between PCBs, enhancing the overall stability of the assembled device.
  3. Space-saving: Castellated PCBs enable vertical stacking of boards, which minimizes the footprint of the assembled device.
  4. Versatility: They can be used in various applications, such as modular electronics, wearable devices, and IoT sensors.

How are castellated PCBs manufactured?

The manufacturing process for castellated PCBs involves several steps:

  1. PCB design: The PCB layout is designed using CAD software, incorporating the desired castellations along the edges of the board.

  2. PCB fabrication: The PCB is fabricated using standard PCB manufacturing techniques, such as etching, drilling, and plating.

  3. Castellations creation: There are two primary methods for creating castellations:

a. Routing: A specialized router is used to cut semi-circular slots along the edges of the PCB. This method is suitable for low-volume production and prototyping.

b. Drilling and milling: For high-volume production, castellations are created by drilling holes along the edges of the PCB and then using a milling machine to remove the excess material between the holes, forming semi-circular slots.

  1. Surface finish: The PCB undergoes a surface finish process, such as HASL (Hot Air Solder Leveling) or ENIG (Electroless Nickel Immersion Gold), to protect the exposed copper and improve solderability.

Designing castellated PCBs

When designing a castellated PCB, several factors must be considered to ensure optimal performance and manufacturability:

Castellation dimensions

The size and spacing of the castellations depend on the specific requirements of the project. Typical castellation dimensions include:

Parameter Dimension
Castellation diameter 0.8 mm to 3.0 mm
Castellation pitch 1.0 mm to 2.54 mm
Castellation depth 50% to 75% of PCB thickness

It is essential to consult with the PCB manufacturer to determine the appropriate castellation dimensions for your project, as these may vary based on the fabrication capabilities and the selected manufacturing method.

Trace routing

When routing traces on a castellated PCB, it is crucial to ensure proper clearance between the traces and the castellations to avoid short circuits and manufacturing issues. The minimum clearance between traces and castellations should be at least 0.15 mm, although larger clearances are preferred for improved reliability.

Solder mask and silkscreen

Solder mask and silkscreen should be applied to the castellated PCB to protect the traces and improve the aesthetics of the board. However, it is essential to ensure that the solder mask and silkscreen do not obstruct the castellations, as this can hinder the soldering process and affect the mechanical stability of the assembled device.

Assembling castellated PCBs

The assembly process for castellated PCBs involves soldering the castellations of one board to the corresponding pads or castellations of another board. There are two primary methods for assembling castellated PCBs:

  1. Hand soldering: For low-volume production or prototyping, castellated PCBs can be assembled using hand soldering techniques. This method requires a steady hand and proper soldering tools, such as a fine-tipped soldering iron and solder wire.

  2. Reflow soldering: For high-volume production, castellated PCBs are typically assembled using reflow soldering. In this process, solder paste is applied to the castellations and the corresponding pads, and the boards are then aligned and placed in a reflow oven. The heat from the oven melts the solder, creating a strong mechanical and electrical connection between the boards.

To ensure a successful assembly process, it is essential to follow best practices for soldering, such as using the appropriate solder alloy, maintaining proper temperature control, and cleaning the assembled boards to remove any flux residue.

Applications of castellated PCBs

Castellated PCBs find applications in various industries and products, such as:

  1. Modular electronics: Castellated PCBs enable the creation of modular electronic devices, where different functional blocks can be easily connected and disconnected as needed. This modularity allows for greater flexibility in device configuration and upgrades.

  2. Wearable devices: The compact size and vertical stacking capability of castellated PCBs make them ideal for use in wearable devices, such as smartwatches, fitness trackers, and medical monitoring devices.

  3. IoT sensors: Castellated PCBs are often used in IoT sensor nodes, where multiple sensors, processing units, and communication modules need to be integrated into a single, compact device.

  4. Automotive electronics: The enhanced mechanical stability provided by castellated PCBs makes them suitable for use in automotive electronics, where vibration and environmental factors can pose challenges to traditional PCB designs.

  5. Space-constrained applications: In applications where space is limited, such as in miniature robots or compact electronic devices, castellated PCBs offer a viable solution for integrating multiple PCBs into a single, space-efficient package.

Frequently Asked Questions (FAQ)

  1. What is the difference between a castellated PCB and a regular PCB?
    A castellated PCB features semi-circular holes or slots along its edges, which facilitate easy and secure connections between multiple PCBs or to mount the PCB onto another surface. Regular PCBs do not have these castellations.

  2. Can castellated PCBs be manufactured using standard PCB fabrication techniques?
    Yes, castellated PCBs can be manufactured using standard PCB fabrication techniques, such as etching, drilling, and plating. The castellations are created using specialized routing or drilling and milling processes.

  3. What are the advantages of using castellated PCBs?
    Castellated PCBs offer several advantages, including simplified assembly, improved mechanical stability, space-saving through vertical stacking, and versatility in various applications.

  4. How small can the castellations be on a PCB?
    The size of the castellations depends on the specific requirements of the project and the capabilities of the PCB manufacturer. Typically, castellation diameters range from 0.8 mm to 3.0 mm, with a pitch of 1.0 mm to 2.54 mm.

  5. Are there any special considerations when designing a castellated PCB?
    When designing a castellated PCB, it is essential to consider factors such as castellation dimensions, trace routing, solder mask, and silkscreen. Proper clearance between traces and castellations should be maintained, and solder mask and silkscreen should not obstruct the castellations.

Conclusion

Castellated PCBs offer a unique solution for creating compact, modular, and mechanically stable electronic devices. By incorporating semi-circular holes or slots along the edges of the PCB, castellated designs enable easy and secure connections between multiple boards or to mount the PCB onto another surface.

The manufacturing process for castellated PCBs involves standard PCB fabrication techniques, along with specialized routing or drilling and milling processes to create the castellations. When designing a castellated PCB, it is crucial to consider factors such as castellation dimensions, trace routing, solder mask, and silkscreen to ensure optimal performance and manufacturability.

Assembling castellated PCBs can be done using hand soldering or reflow soldering techniques, depending on the production volume and specific requirements of the project. By following best practices for soldering and cleaning, a strong mechanical and electrical connection can be achieved between the boards.

Castellated PCBs find applications in various industries and products, such as modular electronics, wearable devices, IoT sensors, automotive electronics, and space-constrained applications. As technology continues to advance and the demand for compact, modular electronic devices grows, the use of castellated PCBs is expected to increase, driving innovation and enabling the development of new, cutting-edge products.