Classification and Functions of Holes on a PCB – A Must-Read! Keep It Collected!

April 25, 2026

Holes on a PCB are categorized into Plated Through-Holes (PTH) and Non-Plated Through-Holes (NPTH) based on whether they participate in electrical connections.

1. Plated Through-Hole (PTH)
A PTH has its hole wall plated with metal. It enables electrical connections between conductive patterns on the inner layers, outer layers, or between inner and outer layers of the PCB. Its final size is determined by the drilled hole size and the thickness of the plated metal layer.

2. Non-Plated Through-Hole (NPTH)
An NPTH does not participate in the electrical connection of the PCB; that is, it is a non-metalized hole.

Classification by PCB Layer Penetration (from top to bottom): Through Hole, Blind Via, Buried Via

1. Through Hole
A through hole penetrates the entire PCB. It can be used for inner layer connections and/or for component positioning and mounting.

• Component Hole: A hole used for fixing and/or making electrical connections with component terminals (including pins and wires).

• Via (for internal connection): A plated hole used for inner layer connections, but not for inserting component leads or other reinforcing materials.

There are two main purposes for drilling a through hole in a PCB:

• To create an opening through the board, allowing subsequent processes to form electrical connections between the top, bottom, and inner layers.

• To maintain structural integrity and positional accuracy for component mounting.

2. Blind Via & 3. Buried Via
Blind and buried vias are widely used in High-Density Interconnect (HDI) PCBs.

• A blind via typically connects Layer 1 to Layer 2. In some designs, it can connect Layer 1 to Layer 3.

• The combination of blind and buried vias enables more connections and higher board density required for HDI. This increases layer density in finer-pitch components while also improving transmission power. Hidden vias help keep the circuit board lightweight and compact.

Blind and buried via designs are common in complex, lightweight, and high-cost electronics such as mobile phones, tablets, and medical devices.

Blind vias are formed by controlled depth drilling or laser ablation, with the latter being more common today. Vias are stacked through sequential lamination. The resulting vias can be arranged in a stacked or staggered pattern, which adds extra steps in manufacturing and testing, thereby increasing costs.

Classification by Function/Purpose:

1. Via: A metalized hole used for electrical interconnection between different conductive layers on the PCB, not for mounting components.
   Note: According to the penetration levels mentioned earlier, vias can be further divided into through vias, blind vias, and buried vias.





2. Component Hole: A hole used for soldering and fixing plug-in electronic components and connectors. It is typically a metalized hole and can also serve as an electrical interconnection between different conductive layers.





3. Mounting Hole: A hole with a relatively large diameter on the PCB, used for fixing the PCB to an enclosure or other carrier.





4. Slot Hole: A slot processed by a drilling machine (automatically converted into a collection of multiple single holes) or by routing. It is generally used for mounting connector pins, such as for the oval-shaped pins of a connector socket.





5. Backdrill: A hole drilled (larger than the preceding PTH) to a specific depth within an already plated through hole. It is used to remove the via stub and reduce signal reflections during transmission.

Auxiliary Holes in PCB Manufacturing (A general understanding is sufficient for PCB design engineers):

1. Registration Hole (Target Hole): Three or four holes located on the top and bottom edges of the PCB, which serve as a reference for all other holes on the board. Also known as target holes or registration holes. They are created using a registration machine (such as an optical puncher or X-ray drilling machine) before the drilling process and are used for pin positioning and securing during drilling.

2. Inner Layer Registration Hole: Holes located at the edges of a multi-layer board. They are used for internal alignment during the inner layer graphic drilling process on the panel.