What is Through Hole Technology in PCBA?

Through hole technology PCBA

Through hole technology presents an alternative to surface mount technology when it comes to assembling PCB boards. If you’re looking to understand this PCB assembly process in a more detailed manner, then we’ve got you covered! This article details the process and its advantages.

What is Through hole technology?

The through-hole technology (THT) is a method of assembling components onto a printed circuit board (PCB) by inserting component leads through holes in the PCB. The components are then soldered to pads on the opposite side.

The term “through hole” comes from the fact that component leads “go through” holes in the board. This technique is typically used for components that are too large to be mounted directly on the board surface, such as connectors and relays.

Through Hole Technology Process

Through hole technology consists of components that have leads that are inserted through pre-drilled holes in the printed circuit board (PCB) and then soldered to pads on the opposite side. Here are the steps involved in the process:

  • The components are placed on the non-soldering side of the board, with their leads inserted through the holes.
  • The components are inspected for correct placement and orientation.
  • The leads are then soldered to the pads on the opposite side of the board. Through hole soldering techniques include wave, selective and manual soldering.
  • The solder is inspected for joint integrity and any excess solder is removed from the board.
  • The PCB may then be cleaned, tested, or otherwise processed before being shipped.

Through Hole Technology Equipment

Depending on the method used for the through hole technology process, a few different types of equipment may be needed. These include:

  • A screen printer, which is used to apply the solder paste onto a printed circuit board
  • A pick and place machine to place components into the correct positions on the board.
  • An oven or wave soldering machine for soldering the through hole components.
  • A chemical bath to clean the board after soldering
  • An x-ray machine and other types of quality control machines for inspecting the PCB assembly for defects
Through hole technology used to assemble components on a PCB board
Through hole technology used to assemble components on a PCB board
Resource: https://forum.fritzing.org

Through Hole Technology Advantages

Despite the through hole PCB assembly process being an older technology, it is still widely used today due to its several advantages. Below are some of the benefits that make the thru hole technology, as it’s also called, a great choice for large or heavy components:

  • It can handle larger and heavier components than surface mount technology. These include connectors, relays and heat sinks.
  • Through hole components are securely held in place due to the leads that penetrate through the board. This provides a better electrical connection than surface mount technology and is more reliable.
  • The through hole technology can be used for double-sided boards since components can be placed on both sides of the board.
  • The electrical connections are more reliable and less prone to failure.

Despite the many through hole technology advantages, there are also some drawbacks to this PCBA assembly method, which must be looked into before deciding whether it’s the right choice for a project. Here are some of these downsides:

  • Components with long wires such as connectors and relays can be easily soldered using THT, but they also take up a lot of space that could be used for other components.
  • It takes more time to assemble THT components than when using surface mount technology, specifically when manual placement and soldering is used.
  • It is more expensive than surface mount technology, since it requires more components and more space or PCB real estate.
  • The fact that holes must be drilled also adds to the costs such as when attaching the leads of a through hole resistor.
  • The boards are bigger and heavier due to the increased component count and the need for larger holes. This can be an issue for some applications such as handheld devices.
Through hole technology components
Through hole technology components
Resource: https://hackaday.com

Through Hole Technology Components

Through hole technology components are usually the larger components that require extra support in the PCB. They also They are also used in high power applications as they provide better heat dissipation and reduce the risk of thermal runaway. Due to their size, these components require extra PCB space and are often more expensive than surface mount equivalents. Some of the types of THT components used for this PCB assembly technique include the following:

  • Connectors: PCB connectors are relatively large components with a number of pins that often protrude from them. They connect electrical components, pass signals, or even connect one board to another.
  • Relays: These are electromechanical devices that can be used to switch current on and off. Because of their size, they are best assembled using the through hole process.
  • Heat sinks: These are metal plates with fins that are used to dissipate heat away from sensitive components.
  • Diodes, transistors and capacitors: These components are used for various applications from small signal amplification to high voltage switching.
  • Switches: These components can be used to control the flow of electricity in a circuit. The THT PCB assembly method offers the best way to mount them.
  • LEDs: A through hole LED (Light emitting diode) is usually soldered directly onto the board using to provide a firmly-secured connection.
  • Resistors: Resistors come in many shapes and sizes, and they are usually attached to boards using the through hole soldering method.


The through hole technology is still widely used today, despite being overtaken by the surface mount method. It provides a reliable and secure connection for components. Components with long pins such as connectors and relays are also best suited for through hole PCB assembly, since they require extra support in the board.

Considering Through-Hole Technology for your project? The choice greatly depends on your specific needs. Discover how our expert through-hole PCB assembly services can be the perfect fit for your project.


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