What are Board Edge Holes?

Board edge holes, also known as edge-plated holes or Castellated Holes, are a type of mechanical feature found on printed circuit boards (PCBs). These holes are located along the edges of the PCB and are used for various purposes, such as:

• Allowing the PCB to be mounted onto another surface or device
• Providing electrical connectivity between the PCB and other components
• Facilitating the attachment of connectors or other mechanical components

Types of Board Edge Holes

There are several types of board edge holes, each with its own unique characteristics and applications. Some of the most common types include:

Type	Description	Application
Castellated Holes	Half-circle shaped holes that are plated with conductive material	Commonly used for mounting PCBs onto other surfaces or devices
Plated Through Holes (PTHs)	Holes that are completely drilled through the PCB and plated with conductive material	Used for creating electrical connections between layers of the PCB
Non-Plated Through Holes (NPTHs)	Holes that are drilled through the PCB but not plated with conductive material	Used for mounting mechanical components or providing access to internal layers of the PCB

Castellated Holes

Castellated holes are one of the most common types of board edge holes. They are characterized by their half-circle shape and are typically plated with a conductive material, such as copper or gold. This allows them to provide both mechanical support and electrical connectivity between the PCB and other components.

Castellated holes are often used in applications where the PCB needs to be mounted onto another surface or device. For example, they can be used to mount a PCB onto a chassis or enclosure, or to connect multiple PCBs together in a stacked configuration.

Plated Through Holes (PTHs)

Plated through holes (PTHs) are another common type of board edge hole. These holes are completely drilled through the PCB and are plated with a conductive material, such as copper or gold. This allows them to create electrical connections between different layers of the PCB.

PTHs are often used in applications where electrical signals need to be routed between different layers of the PCB. For example, they can be used to connect a surface-mounted component on one side of the PCB to a trace on the other side.

Non-Plated Through Holes (NPTHs)

Non-plated through holes (NPTHs) are similar to PTHs, but they are not plated with a conductive material. Instead, they are simply drilled through the PCB and left unplated.

NPTHs are often used in applications where mechanical components need to be mounted onto the PCB, or where access to internal layers of the PCB is required. For example, they can be used to mount a connector or switch onto the PCB, or to provide access to a Ground plane or power plane.

How to Design Board Edge Holes

Designing board edge holes requires careful consideration of several factors, including:

• The size and shape of the holes
• The spacing between the holes
• The conductive material used for plating
• The mechanical and electrical requirements of the application

Hole Size and Shape

The size and shape of the board edge holes will depend on the specific requirements of the application. For example, castellated holes are typically half-circle shaped and have a diameter that is slightly larger than the thickness of the PCB. PTHs and NPTHs, on the other hand, can have a variety of sizes and shapes depending on the components that will be mounted onto them.

When designing the size and shape of the holes, it is important to consider the mechanical and electrical requirements of the application. For example, if the holes will be used for mounting the PCB onto another surface, they will need to be large enough to accommodate the mounting hardware. If the holes will be used for electrical connectivity, they will need to be sized and shaped to provide a reliable connection.

Hole Spacing

The spacing between the board edge holes is another important consideration when designing a PCB. The spacing will depend on several factors, including:

• The size and shape of the holes
• The number of holes required
• The electrical and mechanical requirements of the application

In general, the spacing between the holes should be as small as possible while still providing adequate clearance for the components and mounting hardware. This will help to minimize the overall size of the PCB and reduce manufacturing costs.

Conductive Material

The conductive material used for plating the board edge holes will depend on the electrical requirements of the application. Some common conductive materials include:

• Copper
• Gold
• Silver
• Tin

Copper is the most commonly used conductive material for PCBs, as it provides good electrical conductivity and is relatively inexpensive. Gold and silver are often used in high-reliability applications, as they provide excellent conductivity and resistance to corrosion. Tin is sometimes used as a cheaper alternative to gold or silver, but it has lower conductivity and is more prone to oxidation.

Mechanical and Electrical Requirements

When designing board edge holes, it is important to consider the mechanical and electrical requirements of the application. Some key considerations include:

• The amount of mechanical stress the holes will be subjected to
• The electrical current and voltage that will be passing through the holes
• The environmental conditions the PCB will be exposed to (e.g. temperature, humidity, vibration)

Based on these requirements, the designer will need to select the appropriate size, shape, spacing, and conductive material for the holes. In some cases, additional features may need to be added, such as reinforcement or strain relief, to ensure the reliability and durability of the PCB.

Manufacturing Board Edge Holes

Once the board edge holes have been designed, the next step is to manufacture the PCB. This typically involves several steps, including:

1. Drilling the holes
2. Plating the holes with a conductive material
3. Applying a Solder Mask and silkscreen
4. Testing and inspection

Drilling the Holes

The first step in manufacturing board edge holes is to drill the holes into the PCB. This is typically done using a computer-controlled drilling machine, which can drill holes with a high degree of precision and accuracy.

The drilling process involves several steps, including:

1. Loading the PCB onto the drilling machine
2. Aligning the drill bit with the desired hole location
3. Drilling the hole to the specified depth and diameter
4. Cleaning the hole to remove any debris or burrs

Plating the Holes

Once the holes have been drilled, the next step is to plate them with a conductive material. This is typically done using a process called electroplating, which involves the following steps:

1. Cleaning the PCB to remove any contaminants or debris
2. Applying a conductive layer of copper to the entire surface of the PCB
3. Applying a photoresist layer to the PCB and exposing it to light through a patterned mask
4. Developing the photoresist to remove the unexposed areas
5. Electroplating the exposed areas with the desired conductive material (e.g. copper, gold, silver)
6. Removing the remaining photoresist and etching away the unwanted copper

Applying a Solder Mask and Silkscreen

After the holes have been plated, the next step is to apply a solder mask and silkscreen to the PCB. The solder mask is a layer of polymer that is applied to the surface of the PCB to protect the copper traces and prevent solder from bridging between adjacent pads. The silkscreen is a layer of ink that is applied to the surface of the PCB to label components and provide visual indicators for assembly.

Testing and Inspection

The final step in manufacturing board edge holes is to test and inspect the PCB to ensure that it meets the specified requirements. This typically involves several types of tests, including:

• Continuity testing to ensure that all electrical connections are intact
• Resistance testing to ensure that the plating is of sufficient thickness and quality
• Visual inspection to ensure that the holes are properly aligned and free of defects

If any issues are identified during testing or inspection, the PCB may need to be reworked or scrapped, depending on the severity of the problem.

FAQs

1. What are board edge holes used for?
   Board edge holes are used for a variety of purposes, including mounting the PCB onto another surface, providing electrical connectivity between the PCB and other components, and facilitating the attachment of connectors or other mechanical components.

2. What are the different types of board edge holes?
   The most common types of board edge holes include castellated holes, plated through holes (PTHs), and non-plated through holes (NPTHs).

3. What factors should be considered when designing board edge holes?
   When designing board edge holes, it is important to consider the size and shape of the holes, the spacing between the holes, the conductive material used for plating, and the mechanical and electrical requirements of the application.

4. How are board edge holes manufactured?
   Board edge holes are typically manufactured using a multi-step process that includes drilling the holes, plating the holes with a conductive material, applying a solder mask and silkscreen, and testing and inspecting the PCB.

5. What types of tests are performed on PCBs with board edge holes?
   PCBs with board edge holes are typically tested for continuity, resistance, and visual defects to ensure that they meet the specified requirements. If any issues are identified during testing or inspection, the PCB may need to be reworked or scrapped, depending on the severity of the problem.