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What are Plated Half-Holes/Castellated Holes?

Plated half-holes or castellated holes are plated half holes with half on the edges of the board. They are commonly used for breakout boards or small modules. You may have seen them on some Wi-Fi modules which are then soldered onto a larger PCB similar to the way in which ICs are mounted. Castellated holes are not available for single layer boards. 

How are they manufactured?

Seeed Fusion has adopted a new approach to producing castellated/plated half-holes on prototype boards that increases design flexibility without compromising on quality. There are no restrictions on board shape or panel layout (excluding general rules that apply to all PCB designs made in Seeed Fusion).

Firstly, whole plated through holes are made as usual on the edge of the boards. A milling tool is then used to cut the holes, along with the copper, in half. Since copper is much harder to mill and will likely cause the bit to break, heavy duty milling bits are used at a higher speed. This results in a smoother finish. Each half hole is then inspected in a dedicated station and deburred if necessary.

Plated half holes are available in both standard and Advanced PCB services. For the standard PCB service, the minimum diameter of castellated holes is 0.5mm and they should be separated by a spacing of at least 0.5mm. If you need smaller castellated holes (as low as 0.35mm), please use the Advanced PCB service.  

How to order plated half-holes/castellated holes?

When "Yes" is selected on the order form, any half holes found in the design will be plated with copper:

If "No" is selected, the half holes will not be plated with copper. If there appears to be plated half holes in your design, but the option for castellated holes is not selected, we may contact you directly to confirm whether castellated holes are required.

How to indicate castellated holes in your design?

Castellated hole design varies from software to software, but the end result in the Gerber files should be as follows. Please refer to the documentation of your chosen design software for more information.

Add a via or plated hole directly on the outline of the boards where the plated half hole is required. Ensure that half of the via is on the board and half is on the outside of the outline.  

The following should be included:

- Copper layers (GTL and GBL): Copper pads on both top and bottom copper layers for each castellated hole.

- Solder mask layers (GTS and GBS): Solder mask openings on both sides.

- Drill layer (TXT/DRL): A drill hole for each castellated hole.

- Mechanical/Outline layer (GML/GKO): The outline should cross the drill hole.

- Last modified 2018/08/10

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