Printed circuit board (PCB) is a very important basic part in electronic equipment, which provides a platform for the installation and connection of electronic components. Different PCBs vary in shape, size and design according to the needs of the equipment. The emergence of PCBs allows electronic devices to be miniaturized, lightweight, and mass-produced at a lower cost.

However, here is an often overlooked but very important function in the PCB, that is the mounting hole. These small holes allow the PCB to be firmly attached to the shell or device, ensuring the stability of electronic components installation and protecting the circuit from mechanical stress.

In this blog, let’s deeply talk about what PCB mounting holes are, what types they have, and their differences compared with PCB via holes.

What are PCB mounting holes?

PCB mounting holes are small round holes in the printed circuit board, usually located in the corners or edges of the PCB, ensuring that the board is securely fixed.

The PCB mounting hole has two main functions. One is physical fixation. The PCB mounting hole provides a mounting point for the physical installation of the PCB. By inserting screws or other fixing devices into the mounting holes, the PCB can be securely installed on the shell or bracket of the device. This can prevent the circuit board from being affected by external forces such as movement and vibration during use and ensure its normal operation.

The second is electrical grounding. In some circuit designs, mounting holes can also be used for electrical grounding. This means that through these holes, PCBs can be connected to device shells or other conductive parts. This can help the circuit to achieve a stable potential reference, reduce electromagnetic interference and improve the efficiency and safety of the circuit.

Unlike other types of holes on the PCB, such as through-holes for electrical connections, mounting holes do not transmit electrical signals. They are usually aligned with the design of device shells or other components that fix PCBs.

PCB mounting holes size chart

The size of PCB mounting holes can vary depending on the specific design requirements, the type of fasteners or screws used, and the overall dimensions of the board. Here’s a general size chart for PCB mounting holes based on typical screw sizes:

Common types of mounting holes.

Due to different design and manufacturing requirements, we can divide mounting holes into two types according to whether they are plated: plated mounting holes and un-plated mounting holes.

Plated mounting holes

Plated mounting holes are drilled holes on a PCB that have been coated with a thin layer of conductive material, usually copper, around their inner circumference.

The plating process ensures that the hole has an electrically conductive surface, allowing it to be part of the electrical circuit if needed. This type of mounting hole is often used when the mounting process requires grounding the PCB to the enclosure or other external metal components.

Un-plated mounting holes plated mounting

Un-plated mounting holes, as the name suggests, do not have any conductive coating on their inner surfaces. They are purely mechanical and are used only for physically securing the PCB to its enclosure. These holes are more common in situations where electrical conductivity is not needed, and they simply serve the function of mounting.

Here is a comprehensive comparison between plated mounting and un-plated mounting holes:

Mounting holes vs via holes on a PCB

There are many different types of holes on a PCB, including mounting holes, via holes, component holes, test points and alignment holes. Each of these holes plays a vital role in both the physical structure and electrical functionality of the PCB.

Among them, mounting holes and via holes are the most common holes and people always confuse them. Therefore, it is essential to distinguish the two on a PCB, as they serve entirely different functions, despite both being holes drilled into the PCB.

Via holes are an integral part of the PCB’s electrical design. They allow for the transfer of electrical signals between different layers of the board. In multi-layer PCBs, vias enable connections from surface traces or components to inner-layer circuits, ensuring that electrical signals are routed correctly throughout the board.

Vias are typically much smaller than mounting holes and are filled or plated with conductive material, such as copper, to allow signal transmission.

On the other hand, mounting holes do not carry electrical signals. Their primary function is mechanical: they are used to secure the PCB to a surface or enclosure. While via holes play a crucial role in the electrical operation of the circuit, mounting holes do not, except in specific cases where plated mounting holes are used for grounding purposes.

Conclusion

PCB mounting holes might seem like a minor feature, but they play a critical role in ensuring the durability, functionality, and reliability of electronic devices. Without proper mounting, even the most sophisticated circuit design could fail due to mechanical stresses such as vibration or heat expansion.