In the process of circuit board design, the assembly method and technology of circuit board components have a great impact on the design. If THT is used to assemble the through-hole components, then the design of the through holes is involved accordingly. If SMD to mount, then the board design is different.

Therefore, when designing a printed circuit board (PCB), it is crucial to understand the different types of holes and their role in the assembly of electronic devices. In this article, we will discuss the through hole and its properties on the circuit board, compare the blind hole which is often confused with the through hole, and the surface mount technology corresponding to the through hole technology.

What is a through hole?

A through hole is a hole that runs through the entire PCB. It is an important element in traditional and large-device PCB manufacturing. These holes can be plated (PTH, plated through hole) or non-plated (NPTH, non-plated through hole), and in some cases, through holes are also called vias.

Through holes are commonly used to install and connect through-hole components with leads or pins, including resistors, capacitors, connectors. The pins of these components are inserted into through holes and soldered to both sides of the board, creating a strong electrical connection. Because the pin of the component passes through the entire PCB and is fixed on both sides, the connection is usually stronger than the surface-mount component. In addition, the hole can handle greater current. Therefore, the through hole is often used in high-power electronic components and equipment with high mechanical strength requirements.

Through-hole components: axial and radial

Because the through-hole components are easy to assemble and their connection joints are more solid, they are widely used in the assembly of the circuit board. According to their lead configurations, they can be divided into axial components and radial components, which are respectively applied to specific scenes.

Axial components

The pins of the axial components are located at both ends of the component and extend along the central axis to form a linear arrangement. The pins of the axial components need to be bent at right angles, inserted into holes in the board and installed to the board by soldering. This design is usually suitable for situations where equipment space is limited or a compact layout is required. There are many common axial components such as resistors, capacitors, diodes and so on.

Radial components

Unlike axial components, radial components have pins on the same side and are usually arranged in parallel. The pins of the radial component face inward toward the board, and the component body is perpendicular to the board. Because of the parallel pin design, radial components are more suitable for automated assembly. This configuration is common in electrolytic capacitors and some types of resistors.

Through-hole assembly

Through-hole assembly, the process of inserting components into through-holes and forming mechanical and electrical connections through soldering, often involves several steps.

Component insertion: Insert the pins of the through-hole components through the holes in the circuit board.

Soldering: After the components are inserted, their pins will be soldered to the copper pads on the opposite side of the PCB. Wave soldering is generally used for large batches of through-hole assembly, while manual soldering is used for small batches.

Inspection and testing: After soldering, the solder points of the components need to be checked to ensure the soldering quality. Common inspection methods include automated optical inspection (AOI) and X-ray inspection, which are used to detect soldering defects such as cold solder joints or insufficient solder.

Cleaning: Finally, the circuit board will be cleaned to remove flux residue or any contaminants left over during the soldering process, ensuring the cleanliness and reliability of the product.

Through-hole vs surface mount technology

In addition to through-hole assembly technology, surface mount technology (SMT) is also commonly used in circuit board assembly.

Unlike through-hole technology, surface-mount components are mounted directly on the surface of the PCB without holes. Surface-mount components typically have flat pins or pads that can be fixed directly to the PCB surface by soldering.

As two completely different assembly technologies, through-hole technology and surface mount technology differ in terms such as component placement, assembly process, cost and application suitability. Here’s a detailed comparison of through-hole vs surface mount technologies:

Blind holes vs through holes

During the board design, in addition to considering the use of through-hole or surface mount technologies, it is also very important to pay attention to the different types of holes used in PCBs. Blind holes are also common besides through holes.

What is a blind hole?

A blind hole is a hole that does not extend completely through the PCB. Unlike through holes, blind holes are only drilled to a certain depth of the board and can connect the internal electrical layer without affecting the structure of the other side of the board, which is usually used for the connection of multi-layer PCBs.

Here's a comprehensive comparison between blind holes vs through holes:

Conclusion

Comparing the different hole types in the PCBs, as well as the different assembly technologies, understanding their roles and advantages is crucial to successful PCB manufacturing.