Through-Hole PCB Assembly: Step-by-Step Process Discussed

Dec 17, 2021

Through-Hole Technology (THT) is one of the most common PCB assembly techniques employed today along with surface mount technology (SMT). This technique is developed to effectively mount the electronic components on PCBs. This process is popular due to its simplicity and efficiency. In spite of the availability of advanced PCB fabrication processes, the through-hole PCB assembly technique is adopted in rugged PCB assembly processes. However, before using the through-hole assembly technique, it is important to understand its characteristics and steps involved in this process. This post introduces through-hole PCB assembly techniques, discusses their characteristics, and a step-by-step procedure for the same.

Introduction to Through-Hole PCB Assembly Technique

In through-hole PCB assembly, the components are mounted on boards through the drilled holes, and metal leads are used for the purpose. Once the component leads are inserted through the drilled holes, the leads are then soldered to fix them at mounting locations.

This technique of PCB mounting was highly popular till the 1980s, however today it is commonly employed for building PCB in challenging environments. Let us discuss a few characteristics of the process that make it usable in current times.

Characteristics of Through-Hole Technique (THT)

This technique is used for building durable PCBs due to the following reasons:

It creates strong mechanical bonding between the components.
This technique is highly suitable for mounting bulky components.

Step-by-Step Process of a Through-Hole PCB Assembly

The following steps are performed during the Through-hole PCB assembly.

Pattern Drilling: In the through-hole technique (THT) of PCB assembly, the first step is to drill the holes in a specific pattern. These drill patterns are created by designers during the design process on the layers of the board.
Component Mounting: Once the drill pattern is created, the component leads are inserted through the holes. This type of component mounting can be done manually or by using the automated robotic arm.
Soldering: The soldering process is performed in the following steps.

The drill and the component cap are prepared for soldering. Then, the lead is inserted through the drill and the cap of a component is made to match the surface of the hole. The cap should sit on the surface so that the area below solder remains bent for heat dissipation.
The solder is applied to the connecting surface of the cap and drill.
The solder should be allowed to settle so that the cap and drill surfaces are covered in solder.

Heat Application: Heat is applied to the soldered area so that the cap heats up and solder paste deposits on the required area.
Inspection: Once the solder is deposited and settles at room temperature, the component is fixed at the location of the drill. The open leads are then terminated and then the testing and inspection process is performed. This inspection may include visual inspection, functional testing, flying probe test (FPT), etc.

This completes the process of through-hole PCB assembly. However, the quality of through-hole PCB assembly depends on the expertise of operators handling it. It requires precision and accuracy of drilling, meticulous soldering, etc. This is why you should source these services from trusted manufacturers like Accelerated Assemblies. The company offers high-quality PCB fabrication services and counts some of the top names in defense, aerospace, etc among its clients.