Introduction to PCB Holes: A Comprehensive Guide to Via Holes, Component Holes, and Mounting Holes in PCB

A printed circuit board must have many sorts of holes, such as via holes, component holes, and PCB mounting holes. Each of them has a specific application. This blog will go over several sorts of holes and their applications.

In general, we encounter tiny holes on printed circuit boards that provide connections between different layers, known as via holes. These holes facilitate the transfer of signals or power from one layer to another. On the other hand, there are larger holes without copper pads, known as mounting holes, which are used to securely fasten the PCB to fixtures such as enclosures or box builds. Additionally, there are holes on the PCB specifically designed to accommodate electronic components. These holes allow for the assembly of through-hole pins of components onto the PCB. By categorizing the different types of holes and exploring them in detail, we can gain a comprehensive understanding of their specific characteristics and applications.

Mainly, PCB holes can be classified as follows:

1. Via holes 
2. Component holes 
3. PCB Mounting holes 

There are indeed various categories among the three main types of PCB holes: via holes, component holes, and PCB mounting holes. However, for this blog, we will focus on discussing the conventional via holes and the subcategories of component holes and PCB mounting holes. We kindly request your patience as we explore the subcategories of via holes in detail in an upcoming blog post. This topic holds significant importance and is highly intriguing to understand.

1. Via holes : Via holes should always be Plated Through Holes (PTH) as they enable the feature to connect two or more layers of a PCB. They provide electrical connections from one layer to another. The name "via" itself suggests that we must go through them.

To better understand, consider the example shown in Figure 11. If we want a connection from Point ❶ on the top layer to Point ❷ on the bottom layer, we need to connect the top layer to the bottom layer. Via holes play a crucial role in providing this feature. Refer to the picture below for a clearer understanding of how via holes are connected from the top layer to the bottom layer through plating on the hole walls.

An illustration depicting the cross section of a via hole on a printed circuit board (PCB). The via hole is a cylindrical channel that connects different layers of the PCB. The cross section shows the copper plating inside the via hole, which facilitates electrical connectivity. Adjacent to the cross section is an actual view of the PCB, showcasing multiple via holes dispersed across the board's surface.
Fig.11: Via hole cross section and actual view on PCB

Via holes are typically very small in size. One reason for keeping them small is to save spacing on the PCB, as they are primarily used to provide connections between layers. Additionally, various methods can be employed to protect via holes based on their application. We will discuss the different types of via holes in detail in an upcoming blog.

Types of Via Holes Based on Layer Connections:

(i) Conventional Via
(ii) Blind Via
(iii) Buried Via

There are other types of vias depending on the protection method used for the via. You may wonder why vias need to be protected. The answer lies in safeguarding them from environmental effects and potential issues arising when they are in close proximity to QFN and BGA components. We will cover QFN and BGA components in detail later, but for a quick understanding:

QFN and BGA parts have soldering pins underneath the body, making the pins invisible from the top side. The soldering pins of these components are located directly beneath the body. During the assembly process, in the case of open vias near the component pins, they can become shorted. Therefore, it is necessary to protect vias near QFN or BGA component pins.

Types of Via Holes Based on Protection Method and Advanced Via Types:

(a) Tented Via
(b) Tented + Covered Via
(c) Filled Via - Conductive/Non-conductive
(d) Filled Via + Covered
(e) Plugged Via
(f) Plugged Via + Covered
(g) Filled Via + Capped (Via on Pad)
(h) Stacked and Staggered Via

Please note that the above information provides an overview, and we will delve into each topic in more detail in the upcoming blog posts.

2. Component Holes : Component holes are used for installing electronic components onto a PCB. These holes can be classified as Plated Through Holes (PTH) or Non-Plated Through Holes (NPTH).

In most cases, component holes should be PTH. This is because they are designed to accommodate the component pins and establish electrical connections through the holes. However, in single-layer PCBs where there is only one copper pattern, NPTH component holes can be used since there is no need for plated connections.

NPTH component holes are sometimes used for mechanical support purposes, such as fitting screws or press-fit plastic components into the holes.

Refer to the figure 12 for an illustration of PTH and NPTH types of component holes. Pins 1 to 4 of the component are metal pins that require electrical connections with both layers of the PCB. Hence, PTH holes are necessary to establish connections between the component and the top and bottom layers of the PCB. On the other hand, Pins 5 and 6 of the component are purely for mechanical support. These pins are made of strengthened plastic and do not require any electrical connections. Therefore, NPTH holes on the PCB can be used for these pins.

Please refer to the figure below for a visual representation of the different types of component holes.

An image displaying component holes on a printed circuit board (PCB). There are two types of holes shown: Non-Plated Through-Holes (NPTH) and Plated Through-Holes (PTH). The NPTH holes are represented by simple drilled holes without any metallic plating, while the PTH holes are illustrated with metallic plating, allowing for electrical connections between different layers of the PCB. These holes are used for mounting and interconnecting electronic components on the PCB
Fig.12: Component holes (NPTH and PTH)

3. PCB Mounting holes : PCB mounting holes are used to secure the PCB onto various fixtures or locations as required by the customer. These holes allow the PCB to be mounted within a box build or integrated into the customer's final product. PCB mounting holes primarily provide mechanical support to the PCB and are typically fastened using screws and bolts.

Like other types of holes, PCB mounting holes can be classified as either Plated Through Holes (PTH) or Non-Plated Through Holes (NPTH), depending on the customer's requirements. Let's explore NPTH and PTH mounting holes and their applications with examples to enhance clarity.

(a) NPTH - PCB mounting hole :NPTH mounting holes are used solely for mechanical support without any electrical connection requirement. These holes provide support to the PCB using fasteners and standoffs. Refer to Figure 13, where four screws offer mechanical support to the PCB in a box build with the help of NPTH mounting holes.

An image depicting NPTH (Non-Plated Through-Holes) used as PCB mounting holes. These holes are circular openings on the printed circuit board (PCB) without any metallic plating. They are strategically positioned to facilitate the secure attachment of the PCB to a larger structure or enclosure. The NPTH mounting holes allow screws or other fasteners to be inserted, providing stability and support for the PCB within its intended application
Fig.13: PCB Mounting holes (NPTH)

(b) PTH - PCB mounting hole: PTH mounting holes are used when an electrical connection is required from the PCB to the outside. These holes serve a dual purpose by providing both mechanical support and electrical connection. In Figure 14, four screws not only provide mechanical support to the PCB but also establish an electrical connection to the outside of the box through the red and black wires.

An image illustrating PTH (Plated Through-Holes) used as PCB mounting holes. These holes are circular openings on the printed circuit board (PCB) with metallic plating. They are strategically placed to facilitate the secure attachment of the PCB to a larger structure or enclosure. The PTH mounting holes provide both electrical connectivity between different layers of the PCB and a means for fastening the PCB using screws or other fasteners, ensuring stability and support within its intended application.
Fig.14: PCB Mounting holes (PTH)

In addition to the above types of mounting holes, product developers may require Countersink and Counterbore holes on the PCB. These types of holes are used to accommodate screw heads with a flush or recessed profile relative to the PCB surface. Refer to Figure 15 to understand the concept of countersink and counterbore holes.

Countersink: These holes have a wider diameter to accommodate the angled depth of a screw head. The angled head of the screw requires a countersink hole to ensure it doesn't protrude above the PCB surface.

Counterbore: These holes also have a wider diameter for screw heads, but the screw heads have a flat depth without any angle. Screws with flat heads require counterbore holes to ensure they don't protrude above the PCB surface.

An image demonstrating countersink and counterbore PCB mounting holes. The countersink hole is a conical recess created on the surface of the printed circuit board (PCB), allowing the head of a screw or fastener to sit flush with or below the PCB surface. The counterbore hole is a cylindrical recess that extends partially or fully into the PCB, accommodating the head of a screw or fastener to be recessed below the PCB surface. These specialized mounting holes provide a flush and secure attachment of the PCB to a larger structure or enclosure.
Fig.15: Countersink and Counterbore PCB mounting hole

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