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What are Castellated Pads?

The constant development of electronic devices has increased miniaturization. Also, PCB size keeps shrinking. Therefore, there is a great need to improve the soldering process. Using soldering flux to solder the hole to the motherboard usually leads to cold solder. Therefore, there is an increasing demand for castellated pads.

What is a Castellated Pad?

A pad is crucial for PCB design. In a circuit board, a pad is the exposed area of metal in which the component lead is carefully soldered to. when we talk about castellated pads, we mean vias or PTH located in the PCB edge. Castellations create several half holes. These holes function as pads that create a connection between the PCB and the module board.

Castellated parts are usually applied to the edges of a PCB. Also, they help to solder a circuit board on top of another. Castellations are like indentations created on PCB edges. These castellations make it easy to mount a circuit board on top of another.

Attaching a circuit on top of another creates opportunities for various design options. Castellated pads make the PCB assembly process much easier. However, these castellations may be half holes or a part of a broken circle. Also, these castellations offer good alignment between two circuit boards. Therefore, castellated pads aid the soldering of boards.

Furthermore, castellated pads help the board-to-board soldering. Castellations serve several functions. You can use them in various PCB modules.  The process of creating castellated pads is quite straightforward. Also, this process involves drilling and plating the full holes in the castellated PCB. Furthermore, castellation involves cutting the top region into halves. Therefore, this creates partial or half holes on the circuit board’s edge.

Why is Castellated Pad Crucial in PCB Design?

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Castellated pads can help to replicate some PCB parts. For instance, if a circuit features feedback loops, an inverter, or a filter, you can produce these sub-circuits and then solder them on the main circuit.

  • Castellated pads can change the pin layout of the component based on user requirements.
  • Castellation makes it easy to mount circuit boards to another PCB
  • Also, a castellated PCB can serve as a breakout board for a certain part of your larger circuit board.
  • They help in combining two circuit boards to validate the quality of solder joint.
  • Castellated pads can help you design integrated modules on a PCB.
  • Also, they are suitable for use in small modules like breakout boards and Wi-Fi modules.
  • Castellated pads enable complicated components to be integrated with a breadboard.
  • They enable electrical connection to another board via the edges of the board without the need for additional components.

Recommended Specifications for Castellated Holes

There are some recommended design specifications for castellated holes.

Size

Use the biggest size available, this will help you mount PCB correctly

Pad design

It is much better to use the biggest pad. Integrating the largest pad for every castellation enables the PCB to fit well

Distance and diameter

Half holes are ideal for use in both advanced and standard circuit boards. The minimum hole diameter for a standard circuit board should be 0.6mm. Also, the castellated holes diameter for advanced circuit boards should be smaller. Note that the minimum distance between two castellations should not be lower than 0.55mm.

Surface finish

The surface of a circuit board is crucial for mounting PCB correctly. Also, ENIG finish is one the best surface finishes for circuit boards. However, the intended application of the PCB will determine the type of surface finish you opt for.

How to Design a Castellated Board

pcb castellated holes

You have to ensure high yield and quality when designing a castellated board. The process of designing a castellated circuit involves designing castellated pads. Also, this process is a complex one. However, any costly mistake will affect the performance of your circuit board. You need to understand some things when designing a castellated pad.

Half hole PCB

Half hole board features a part of a broken circle. When designing this castellation, the PCB designer must be aware of some crucial things. Below are factors to consider when designing half hole.

  • Holes with smaller lead-in holes

These holes are ideal for use in any connector application. Also, they require a cutting tool which helps in creating other smaller castellations where needed.

  • Use the bottom and top edge as the location of the hole

Avoid utilizing the vertical edges. This is because these edges usually function as bridges. Therefore, this ensures the circuit board bridges in place.

There are various designs for half holes. However, they vary based on their software.

How to Fabricate a Circuit Board Castellated Pads

When fabricating a circuit board with castellated pads, you need to ensure high yield and quality in the process. However, castellated circuit boards don’t appear to fit in the PCB fabrication process. Therefore, you can ensure the design passes through fabrication. You can achieve this by simply modifying the Gerbers to specify drill hits. This usually needs the following drill files (TXT/DRL) and copper layers (GBL and GTL).

Some fabricators believe that the best alternative to castellated boards is integrating solder pads to mount the module. However, the main challenge here is the possibility for contamination. Too much of solder paste along the pad array can lift the module.

The manufacturing process for castellation pads involves the following steps:

  • Drilling of holes
  • Ensuring plated hole
  • Creating panel plating
  • Performing image transfer
  • Performing pattern plating
  • Striping
  • Etching
  • Solder masking
  • Surface coating
  • Integrating plated half holes

Frequently Asked Questions

What are the applications of Castellated Pads?

The castellated pads on circuit boards serve good purposes in several industries like:

What are the steps involved in castellated pads design?

The creation of castellated holes involves drilling and plating the full holes in the PCB. These holes are similar to half circles on the PCB edges since they are partially cut to create a half hole.

Conclusion

Castellations serve several functions. You can use them in various PCB modules. This article has explained the importance of castellated pads in PCBs. Also, castellations are useful in several industries.