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through hole pcb assembly



Expert Guide to Through Hole PCB Assembly: Techniques and Benefits


Early electronic project creation used the point-to-point manufacturing process. But in the 1950s, the 2nd generation of computer electronic projects made on PCB board were created using through-hole technology. With the advances in technology, SMT is introduced, replacing the older Through-hole technology, but in larger power projects, THT is still used. Currently, primarily SMT-based boards are created, but for interconnections of different layers of PCB boards, stills are made using through-hole technology, such as other types of board vias like through-hole vias. This post will look at Through-hole technology and its differences from SMT.

What is through-hole PCB assembly?

Through-hole PCB assembly is a technique in which components are connected on board, passing their leads through drilled holes on the surface of the PCB board. When components' leads are passed through, holes are soldered on both sides to make conductive paths. Manual or reflow soldering is commonly used to make strong connections between board components. 

Different types of PCB boards are used in electronic projects: single-sided, double-sided, or multiple-layer. In older electronic projects, they were made with single or double layers, and these boards were made using through-hole technology, but multilayer boards were commonly used with advanced technology. In these boards, through-hole technology did not fulfill the electronic needs as it took more places for component placement, so it was replaced with SMT technology. 

However, through-hole is still used in different projects and as a combination of SMT. Its use in larger-size projects is preferred since any component damaged or has to be repaired can easily be separated from the board compared to SMT components. Their stable structure makes them suitable for use in projects where high thermal stress is involved. In the 1980s, when SMT became everyday use, it was thought that THT would soon end, but still, it is used and has importance in the electronic industry.



Advantages & Disadvantages of Through Hole PCB Assembly

 Through Hole PCB Assembly Advantages

    ● This process handles more significant-sized components, and it is used in high-power components in electronics and industries where larger power-consuming machines are used.

    ● There are strong connections of components on the board with the use of the THT technique since it involves the soldering of components on both sides of the board selpt. Strong component connections ho have a high-strength board that easily handles stress and environmental conditions like temperature and pressure changes.

    ● Larger boards are made with this process to dissipate heat from components quickly. So, it is used in power electronics since it needs a high power management process.

    ● In this assembly component, repair is an easy process.

Through Hole PCB Assembly Disadvantages

    ● THT assembled board does not provide the required density for projects since it makes less dense boards. In high-density design, instead of THT, SMT is used since it can be small components in high-density layout.

    ● It is not used for less-weight projects; a small size is needed since THT components are more significant than. SMT components.

    ● This is a slow process since it uses a manual component connection process. That makes it a more costly and time-consuming method than SMT.

Applications of Through Hole PCB Assembly 

    ● It is used in industries to make high-weight machines that operate at different temperatures. It is used to ensure the reliable operation of sensors and control systems.

    ● It is used in medical devices, such as diagnostic and implantable devices.

    ● Automobile electronics that come with an engine control system use THT. This process helps to make components strongly connected to handle high temperatures and vibrations.

    ● Devices used in aviation also use THT to connect components since the aviation industry needs high mechanical strength components.

    ● It is also used to make military tools that can operate under challenging conditions and handle harsh weather. 

The Process of Through Hole PCB Assembly 

There are three common steps of the THT assembly process.

  • Component Insertion

    • In this process, pins of THT components, like resistors, diodes, etc., pass through the holes made on boards.

  • Soldering:

    • They are soldered after passing the component pins or leads in the holes on board. That is, the metallic alloy has a lower melting point and connects the leads of components on board. This process ensures a solid electrical path. The types of soldering commonly used in THT are wave and selective soldering. Wave soldering is used for high-volume THT assembly. While selective soldering uses a solder molder to apply molted solder to make connections

  • Cleaning:

    • In this step, residual flex on the board is removed. Flux residues are removed during soldering to avoid corrosion and electrical interference. For the cleaning process, brushes and solvents are used.

Innovations and Trends in Through Hole PCB Assembly 


  • As it is an old assembly process, it has adapted to miniaturization. The use of advancements and new manufacturing techniques helps to make small and less THT components have compact designs.

Lead-Free Alloys

  • Due to environmental safety, industries are using lead-free solder alloys. This adaptability of lead-free alloys is due to eco-friendly manufacturing techniques used in through-hole assembly.

Selective Soldering 

  • With the use of selective soldering machines, THT has become able to solder certain components at specific points. This process minimizes the chances of thermal stress on sensitive parts and increases the quality of the solder joint.

Advanced Flux 

  • Flux is considered the main component of soldering that has made some advancements. Using the latest flux process, we can get reliable THT since it has wetting features and fewer chances of errors due to good solder flow.


  • The features of THT assembly that allow us to adapt different component types and their sizes make it best to provide features like customization, prototyping, and high flexibility.

Challenges in Through Hole Assembly 

     ● This technique does not get high component density on board since it involves holes that also need some space to create. The solution to this limitation is using THT with SMT, a hybrid assembly process.
     ● Another limitation is that it requires manual labor for component insertion in the holes, making it costly and slow. To solve this issue, use robotic component insertion techniques that have fewer chances of error and reduce time and cost.
     ● Wave soldering is used in this process since it has a high heat that affects the sensitive component. So best option is to use selective soldering instead of wave soldering to target the specific part on board and affect the neighboring parts.
     ● It is best to use the miniaturization features of the through homes component to make a compact device that is helpful since it produces less weight in the THT process than the SMT components.

Best Practices for Efficient Through Hole PCB Assembly 

   1.The quality of sensitive board components can be maintained with selective soldering that reduces thermal stress on another component, the targeted part of the boards.

   2.Manual labor for THT is costly, so using an automated component connection process minimizes the cost and makes effective connections. Automatic machines connect more components in less time than manual component connections.

   3.Using an accurate cleaning method for flux residues avoids the effects of corrosion and any defects on board and, as a result, increases the efficiency of THA.

THT assembly can be made an effective process for electronic assembly if it uses the quality flux formulation and lead-free solder alloys that are less hazardous to the environment


THT is the best PCB mounting technique for making larger-sized boards or multiple layers. It is a cost-effective solution for prototypes and board testing and is also preferred for high mechanical strength component mounting.

However, it is preferred for something other than high-density design where SMT makes high-speed assembly less weight board. All in all, using either SMT or THT is based on the type of project and its requirements. For high-density projects, SMT is preferred, and for larger-size and high-power projects, THT is used. 

For more information about your PCB-based project and which type of assembly it needs, contact PcbBasic, the best PCBA manufacturer


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