What are Castellation PCBs?

A particular type of PCB design is known as a castellation PCB (Printed Circuit Board), which has small plated half-holes or notches around the board’s edges. These holes are known as castellation holes, which make it simpler to solder the board and join the PCB to other panels or sections. In surface mount technology (SMT) applications, where components are put directly onto the board’s surface, Castellation PCBs are frequently utilized. This is a typical method for assembling PCBs.

What are Castellated Holes?

Castellated holes are used for setting up an electrical and mechanical connection between two different PCBs or between a PCB and another module. Castellated holes are shaped like a castle’s battlements, with notches or teeth running along their edges. They are placed on a PCB’s edges. It is simpler to solder the PCB straight onto another board or module due to the notched edges.

Why are Castellation PCBs used?

Compact size, multifunction, and high density have increased with the growth of electronic products. The PCBs’ size is continuing to decrease, while the boards’ geometric index is rising daily. Consequently, a change to the soldering procedure is also required. Cold solder will come from using soldering flux to connect the circular hole to the motherboard. The daughterboard and motherboard will have a poorer electrical connection as a result, primarily because of how big the hole is. The electronic device won’t function properly as a result. Thus, the need for plated half-holes is growing every day.

A PCB board’s edges are dedicated to the castellated holes. They may duplicate a PCB circuit’s majority of its components. Assume we have an inverter or filter in our circuit. These little sub-circuits are mass-producible. After that, we may connect them to the main PCB board that carries the circuit’s other components. The castellated holes so copy that specific area of the main printed circuit board.

The following are some applications for castellations:

  • A smaller section of a larger PCB can use castellated PCBs as breakout boards.
  • Castellated holes connect two PCB boards and confirm the solder joint’s reliability.
  • Wireless PCB-to-PCB links can also be created using castellated holes.
  • We can produce integrated modules on a single PCB using this technique. These modules can support additional PCB assembly steps.
  • We are able to customize the component’s pin arrangement to our preference by using these castellated holes.
  • This technique is commonly used with breakout boards or small modules such as Wi-Fi modules.

Types Of Castellation:

Full Castellations:

A printed circuit board (PCB) with its entire edge notched to create a series of extensions resembling a castle’s battlements is known as a full castellation. Because the castellations may be soldered straight to matching pads on the mating board, this design facilitates simple soldering and electrical connections between two PCBs. When a PCB module or daughterboard needs to be safely attached to a main PCB, as in wireless communication modules or sensor boards, full castellations are frequently used. Castellation PCBs frequently use PCB modules to offer extra features and functionality. A printed circuit board (PCB) module is a compact circuit board intended for integration into a larger PCB or system.

Staggered Castellations:

Staggered castellations are a variant of full or partial castellation designs in which the notches are spaced apart along the PCB’s edge. Full castellations are one kind of castellation design. This arrangement can increase the mechanical stability of the joint between two boards since the stress is distributed more equally throughout the solder joints due to the staggered pattern. Staggered castellations are frequently utilized in high-vibration settings or in applications (like automotive or aerospace electronics) where the PCB connection may be mechanically stressed.

Partial Castellations:

Similar to full castellations, partial castellations or half castellations have notches on only a piece of the PCB edge. This arrangement is typically used when constraints on space prevent the use of full castellations or when only certain areas of the board need electrical connections. Applications where a PCB needs to be connected to a flexible circuit, like tiny power supply modules, need for partial castellations.

Mechanisms for Castellation

To maximize the electrical and mechanical performance of the connection, a number of standard configurations can be used in addition to different types of castellations. The choice of castellation type and configuration for use is determined by the particular needs of the application, including the desired electrical performance, mechanical stability, and available space. Each castellation type and pattern has unique advantages and compromises. Among these configurations are:

  • Single-row castellations: Along the PCB’s edge, a single row of notches is made. The most popular and basic design, it can be used for a variety of purposes.
  • Double-row castellations: On the edge of the PCB, two parallel rows of notches are made to improve mechanical stability and boost connection density. When more mechanical support is needed or in high-density interconnects, double-row castellations are frequently used.
  • Interleaved castellations: Each notch in a row is offset from the notches in the row next to it, creating an interleaved pattern in the castellations’ notches. Through a reduction in crosstalk and signal interference between adjacent connections, this arrangement can offer better electrical performance.

Basic Guidelines for Castellated PCBs Holes:

Here are some recommendations regarding Castellated Holes’ specifications. There are various design features that you should consider while using castellated holes for PCB soldering. You need to stick to these qualities while making sure everything is done correctly. The following is a list of suggested measurements for castellated holes:

  • Pad Design: It is preferable to use the largest pad that is available for use. The castellation PCBs fit together correctly when the largest possible is used for each one.
  • Diameter and Distance: Both standard and advanced PCBs use castellated holes. The minimum castellated hole diameter for typical PCBs is 0.6 mm. The castellated holes on modern PCBs should have a lower diameter as possible. There should be a minimum of 0.55 mm between two castellated holes.
  • Surface Finish:  You must carefully consider the surface finishing in order for the PCBs to mount appropriately. For PCBs, ENIG finish can be the ideal surface finish. However, based on how the boards will be used, you can select the finish type that you like most.

Some basic suggestions are:

  • Identify the requirement for castellations in your IoT device.
  • To ensure the correct alignment with the mating board or module, take into account the orientation of the castellated holes.
  • Based on how you solder and assemble the castellations, determine the right size and shape for them.
  • The number of holes on the board is always kept to a minimum when utilizing castellated holes for soldering. Looking for the ideal number of castellated holes can greatly improve alignment and assembly ease. But the number of holes should always match the pattern of the boards.
  • Enough space should be left between castellations during assembly to avoid solder bridging.
  • Choose PCB material that not only supports the castellation’s durability but also satisfies the mechanical and electrical requirements of your application.
  • To avoid unwanted solder connections, apply a solder mask to areas that are not supposed to be soldered.
  • Make sure your PCB manufacturer has clear assembly instructions that include information on solder paste application, alignment, and reflow profile.
  • Carry out the PCB testing procedures, making sure to test the electrical connections’ continuity.
  • Consider the temperature, humidity, and other environmental factors when selecting materials and finishing for your IoT device.
  • Cooperate closely with your PCB manufacturer, keeping lines of communication open and attending to any queries or worries they might have while the product is being manufactured.

You can create castellated PCBs that precisely match the requirements of your IoT device by taking all of these factors into account, ensuring reliable service as well as ease of assembly. To achieve the best performance, the design can be improved with frequent testing and cooperation with experienced PCB manufacturers.

Read More: Soldering Techniques for Printed Circuit Boards (PCBs)

How Castellated Holes are Designed in Altium:

There are a number of ECAD tools in the market to meet the standards of PCB design. Some of them are Allegro, cadence, Eagle, Altium Designer, and Kicad. Altium has a strong and adaptable PCB design tool has support for castellation PCB. Designers may effortlessly generate and enhance castellation patterns, oversee pad designs, and guarantee appropriate inter-castellation spacing with its sophisticated routing and layout capabilities. Additionally, design rule checks (DRC) are integrated into Altium Designer to assist in locating and resolving possible problems prior to manufacturing.

Following are the steps to design single-edge castellated holes as components.

1) Select a pad from a toolbar and place it.

 2) Double-click on the pad and select properties. Now add the following parameters of the pad.

 Hole size=.76mm

 X size= 1.5mm

 Y size= 1.5mm

3) Select a line and place a rectangular region with the following parameters.

4) Now select an arc from the toolbar and place it on the edge of the pad. Select the width of the arc as 1mm.

5) Select all lines along with the arc, go to the toolbar select the following, and convert into a region.

6) Make a solid region and paste the same region into the following layers as it is.

  • Top layer
  • Bottom layer
  • Top solder
  • Bottom solder
  • Top paste
  • Bottom paste

7) One castellated pad is created. Now place it at a distance of 2.54mm and make it a component.

A screenshot of a computer Description automatically generated

You can check it in a 3D view as well.

How Castellated Holes are formed on PCB?

Drilling plated through holes around the board’s edges makes castellated holes. Fabricators must divide the holes along the edge into halves after drilling and then attach the pad to it. The subassembly circuits can be soldered to the main board using these plated semi-holes as soldering pads. These holes are made using a procedure known as side plating or edge plating.

Make sure that there is no gap between the two boards while soldering because it will have adverse effects electrically and mechanically.

Castellation PCBs have many benefits in a range of applications, such as wearable technology, game consoles, consumer electronics, and smart home systems. They are the perfect option for connecting and integrating electronic components because of their small size, simplicity of installation, and enhanced electrical performance. Engineers and manufacturers may optimize their designs for performance, reliability, and manufacturability, eventually improving the end-user experience by understanding the design, manufacturing, and testing procedures involved in generating castellation PCBs.