HomeTips & GuidesThrough-hole PCB assembly: Is It better than surface-mount PCB assembly

Through-hole PCB assembly: Is It better than surface-mount PCB assembly

About Through-hole PCB assembly Modern electronics come with printed circuit boards or PCBs, which connect and support all the electronic components so the device can function smoothly. 

As a manufacturer, you must maintain the quality of the printed circuit boards. Any defect can lead to a damaged product, cause safety issues, or even damage the reputation.

The main task that determines the quantity of PCBs is the assembly process. There are two assembly methods: through-hole technology and surface mount technology.

Let’s find out in this article which method can help you get high-quality printed circuit boards.

Table of Contents

Overview of the PCB assembly process:

The overall manufacturing process of the PCB assembly is completed in various steps depending on the project. 

When the plain board and the design are ready, the PCB assembler completes the process in various steps.

  • Based on the design, the PCB assembler puts all the components on the bare board. He may choose either of two methods: through-hole or surface mounting. The chosen technology determines how this process proceeds.
  • After completing the assembly process, the PCB assembler does all the other checks. All such inspections aim to find out any potential problems in the assembly. Sometimes, they perform only visual checks; at other times, they use AOI equipment to discover lead-level and component defects.
  • After all the tests, an assembler performs in-circuit testing to verify the PCB functionality.
  • Once the inspection is complete, the assembler removes all the dirt, oil, and leftover flux from the board. The professionals may use high-pressure deionized water to clean the residue. Ions in regular water damage electronic circuits; thus, professionals use deionized water.

What is the thru-hole PCB manufacturing process?

The name clears that through-hole technology involves drilling holes in the board. 

  • Based on the PCB design, the professionals drill holes in the board to allow components to go through them.
  • After putting all components’ leads in the holes, the assembler will inspect and adjust the components if required, considering the right polarity and orientation. 
  • Finally, he will solder all the leads using the wave soldering method, through which the board gradually passes over the solder liquid at a very high temperature.

Earlier, all these processes required manual efforts. However, the invention of automatic insertion mount machines helps complete all these processes in much less time.

Through-hole components are of two types: radial lead and axial lead. In the radial ones, the leads are on one side, while in the axial ones, the leads are present on both ends.

The axial leads come out of the components in a straight line.

On the other hand, radial leads run through the entire PCB to connect its different layers.

Through-hole technology PCB

Through-hole technology PCB

What is the Surface Mounting process?

Like the thru-hole process, professionals mounted the components on the board manually. However, with the advent of modern technology, the process has become automatic.

Here are the steps required to complete the SMT process:

  • Step 1: The assembler puts solder paste on the different parts of the boards where he will place the components. Assemblers mostly use a solder screen or a stencil to ensure the paste applies at the correct positions.
  • Step 2: The assembler examines the board for problems in the solder paste printing process. If he finds any issue, he will remove the paste from that location and reapply it, which is important because the quality of solder paste printing essentially decides the quality of the soldering process.
  • Step 3: After a thorough inspection, the professional places all the components on the PCB according to the design. Earlier, professionals used tweezers to mount all the components. However, these days, automatic pick-and-place machines do all the work.
  • Step 4: After putting all the components, the assembler puts all the components into the pads on the circuit board. For this, they use a reflow soldering process where they send the PCB through a furnace so that its high temperature melts the solder paste and liquefies it.

The SMT process uses a different method to connect all the board layers because there are no holes. They use vias, like small holes connecting different board layers.

However, no leads connect directly to holes in thru-hole technology. The vias here are of various types, such as blind vias, through visa, or buried vias.

If you use surface mount technology, you must use unique components. These surface mount components or devices function similarly to those of thru-hole components.

However, their design is different from those used in the SMT process.



Through-hole PCB assembly mounting process vs. surface-mount PCB assembly mounting process

Thru-hole PCB assembly is an old process of manufacturing printed circuit boards. Gradually surface surface-mounted technology came into the market. 

Initially, it looked as if this new SMT technology would make the thru-hole assembly process obsolete. 

However, the thru-hole assembly process still has many benefits over other technology.

Through-hole PCB assembly: Process

In THT, manufacturers insert components through holes drilled in the board, while in SMT, components are soldered on the pads present on the board.

Through-hole PCB assembly: Advantages


  • Components have higher reliability.
  • Components form strong bonds as leads pass through all the holes and get soldered in one place.
  • The high reliability of the components makes them suitable for use in applications involving impacts, shocks and environmental stresses.
  • The process is suitable for larger units as there is no concern for using small components to reduce costs.
  • The technology is good for products that require high reliability and the ability to bear mechanical stress.
  • The process is good for prototyping and testing, as you can adjust the leads and try different layouts.


  • SMT requires smaller boards than the THT process almost one-third in size and one-tenth in weight).
  • It allows a high density of components on the board, which enables more connections on a single board. You can mount components on either side (opposite each other) to use more board space.
  • The process is fast and easy and thus cost-effective, too. Further, it is automated, reducing costs.



The process is unsuitable for high-density PCB boards as its component size is larger. As they take up more space, the need for higher space leads to higher costs.


Surface mount components are not as secure as those in which leads pass through the board. Thus, they are unsuitable for environmental stresses or where reliability is essential.



  • It is good for capacitors, semiconductors, plug-connectors, etc.
  • You can also use it for military, industrial and aerospace applications.
  • Outdoor light-emitting diodes also use this technology as it can withstand harsh outdoor conditions.


  • It is suitable for most modern electronic hardware, such as tablets, smartphones, laptops, and other Internet of Things (IoT) devices. Today, most electronic hardware employs surface-mount technology.
  • It is also good for communication, telecom, industrial hardware, medical equipment, transport devices, etc.


Both thru-hole and surface mount technologies have their own advantages and applications. You have to choose as per your requirements. 

For the proper functioning of any PCB, the cables transmitting power and control signals to it should be high quality.

If you are looking for custom cables for your PCB systems, contact Cloom. We have advanced manufacturing processes to deliver custom cables to our diverse client base.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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