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Demystifying THT PCB Assembly: A Comprehensive Guide

In the ever-evolving world of electronics manufacturing, through-hole technology (THT) PCB assembly remains a crucial process for many applications. This comprehensive guide delves into the intricacies of THT assembly, exploring its processes, techniques, advantages, and future trends. Discover the unique strengths of THT and how it complements surface mount technology in modern product designs.
Through Hole Technology

What is THT PCB Assembly?

In the world of electronics manufacturing, through-hole technology (THT) PCB assembly remains an essential process for many applications. While surface mount technology (SMT) has gained widespread popularity for its compact designs and automation capabilities, THT assembly still plays a crucial role, particularly for products requiring larger components or high-power handling.

THT PCB assembly, also known as through-hole assembly, involves mounting electronic components by inserting their leads through pre-drilled holes in the printed circuit board. This traditional assembly method has been around for decades and continues to be widely used in various industries, from consumer electronics to industrial equipment.

Compared to SMT assembly, the THT process typically requires more manual intervention and may have a lower component density. However, it offers several advantages, including the ability to handle larger components, better heat dissipation, and a more robust mechanical connection between the components and the PCB.

In this comprehensive guide, we’ll dive deep into the world of THT PCB assembly, exploring its processes, techniques, advantages, and applications. Whether you’re a hobbyist, an engineer, or a manufacturing professional, this guide will provide you with valuable insights into this time-tested assembly method.

Circuit board with DIP components
Circuit board with DIP components

The THT PCB Assembly Process - A Detailed Look

At the heart of THT PCB assembly lies a methodical sequence of steps that transform a bare printed circuit board into a functional electronic device. This multi-stage process demands precision, careful handling, and adherence to industry standards to ensure reliable and high-quality end products.

  1. Component Preparation
    Before the assembly process can begin, the required through-hole components must be carefully prepared. This typically involves inspecting the components for any defects or damage and ensuring that their leads are properly formed and trimmed to the correct length for insertion into the PCB.
  2. Through-Hole Component Types
    There are various through-hole component types utilized in THT assemblies, each serving specific functions within the circuit. Common examples include resistors, capacitors, diodes, transistors, integrated circuits (ICs), connectors, and electromechanical components like switches and relays.
  3. Types of Through-Holes
    The holes drilled into the PCB for THT assembly can vary in size and shape, depending on the requirements of the components being mounted. Some common types of through-holes include:
  • Plated Through-Holes (PTHs): These holes are lined with a conductive material, typically copper, to facilitate electrical connections.
  • Non-Plated Through-Holes (NPTHs): Unplated holes used for mechanical purposes or to allow air flow.
  • Vias: Smaller plated or non-plated holes that enable connections between different layers of the PCB.
  1. Component Insertion
    Once the components and PCB are prepared, the through-hole components are carefully inserted into their respective holes on the board. This process can be performed manually or with the aid of automated insertion machines, depending on the production volume and complexity of the assembly.
  2. Soldering
    After component insertion, the leads protruding through the PCB must be securely soldered to establish reliable electrical and mechanical connections. Two common soldering techniques used in THT assembly are:
  • Wave Soldering: The PCB is passed over a wave of molten solder, allowing the leads to be soldered simultaneously.
  • Hand Soldering: Each component lead is individually soldered using a soldering iron and solder wire, typically employed for low-volume or prototype assemblies.
  1. Cleaning and Inspection
    Following the soldering process, the assembled PCB thoroughly cleans to remove any residual flux or contaminants. Finally, the assembly is visually inspected or using advanced techniques like X-ray inspection, to ensure proper solder joints and identify any defects or issues.

By meticulously following these steps, THT PCB assembly techniques produce robust and reliable electronic devices capable of withstanding harsh environments and handling high power requirements.

Soldering a through-hole component on a PCB
Soldering a through-hole component on a PCB

THT PCB Assembly: Pros, Cons, and Comparison with SMT

While THT PCB assembly has stood the test of time, it’s essential to understand its advantages and limitations compared to the more modern surface mount technology. This analysis will help determine the most suitable assembly method for your specific application.

Advantages of THT PCB Assembly:

  1. Ability to accommodate large components: THT excels in mounting sizeable components, such as transformers, heat sinks, and high-power devices, which are challenging to incorporate using SMT techniques.
  2. Enhanced mechanical robustness: The through-hole leads of components inserted into the PCB provide a sturdy mechanical connection, making THT assemblies more resistant to vibrations and physical shocks.
  3. Better heat dissipation: The protruding leads of through-hole components facilitate efficient heat dissipation, making THT assemblies well-suited for high-power applications.
  4. Cost-effectiveness for lower volumes: For low to medium production volumes, THT assembly can be more cost-effective than investing in specialized SMT equipment and infrastructure.

Disadvantages of THT PCB Assembly:

  1. Lower component density: THT assemblies generally have lower component density compared to SMT, as through-hole components require more board space due to their leads and the larger hole sizes.
  2. Increased manual intervention: While automation is possible, THT assembly often involves more manual processes, such as component insertion and hand soldering, leading to higher labor costs and potential human errors.
  3. Longer assembly times: The multi-step process of THT assembly, including component insertion, soldering, and cleaning, can result in longer production times compared to highly automated SMT lines.
  4. Potential reliability issues: Improper soldering or excessive heating during the wave soldering process can lead to potential reliability issues, such as cold solder joints or component damage.

Comparison with SMT Assembly:

  • Component density: SMT assemblies achieve significantly higher component densities, enabling more compact and lightweight designs.
  • Automation: SMT assembly processes are highly automated, leading to increased production efficiency and reduced labor costs.
  • Precision: SMT components are precisely placed on the PCB surface, often with the aid of specialized pick-and-place machines, resulting in higher accuracy and repeatability.
  • Lead-free compatibility: SMT assembly is better suited for lead-free solder paste and processes, aligning with environmental regulations and sustainability goals.
  • Mixed assemblies: Many modern electronic products incorporate both THT and SMT components, leveraging the strengths of each assembly method.

While SMT has become the predominant choice for high-volume electronics manufacturing, THT assembly remains a valuable technique, particularly for applications requiring large components, high-power handling, or cost-effective low-volume production.

Technician hand soldering DIP components on a printed circuit board
Technician hand soldering DIP components on a printed circuit board

Common Types of Through-Hole PCB Assembly Techniques

While the fundamental principles of THT PCB assembly remain the same, various techniques have emerged to cater to different production requirements and application needs. Understanding these methods is crucial for selecting the most suitable approach for your project. Let’s explore the common types of through-hole assembly techniques:

  1. Manual Through-Hole Assembly
    In manual THT assembly, skilled technicians insert components into the PCB by hand and solder each lead individually using a soldering iron and solder wire. This method is suitable for low-volume production runs, prototyping, or assemblies requiring a high degree of precision and manual intervention.


  • Cost-effective for small batches
  • Allows for customization and modifications
  • Suitable for complex or irregularly shaped components


  • Labor-intensive and time-consuming
  • Potential for human error and inconsistencies
  • Difficult to scale for high-volume production
  1. Wave Soldering
    Wave soldering is an automated process widely used in high-volume THT assembly. Components are first inserted into the PCB, either manually or using automated insertion machines. The board is then passed over a wave of molten solder, allowing all leads to be soldered simultaneously.


  • High throughput and production efficiency
  • Consistent solder joints
  • Suitable for large-scale manufacturing


  • Requires specialized wave soldering equipment
  • Potential for thermal stress on components
  • May not be suitable for mixed THT/SMT assemblies
  1. Selective Soldering
    Selective soldering is a specialized technique used for assemblies that combine both through-hole and surface mount components. Instead of subjecting the entire PCB to molten solder, selective soldering precisely applies solder to specific areas, protecting sensitive SMT components.


  • Enables mixed THT/SMT assemblies
  • Minimizes thermal exposure to SMT components
  • Precise solder application


  • Requires advanced selective soldering equipment
  • Longer setup times for programming solder locations
  • More complex process compared to wave soldering
  1. Automated Through-Hole Assembly
    Automated THT assembly involves the use of specialized robots and machinery to insert components into the PCB and solder them in place. This highly automated approach is suitable for high-volume production runs, ensuring consistent quality and minimizing human intervention.


  • High throughput and production efficiency
  • Consistent component placement and soldering
  • Reduced labor costs


  • Substantial investment in automation equipment
  • Limited flexibility for product changes or customizations
  • Potential for high setup and changeover times

By understanding the strengths and limitations of each THT assembly technique, manufacturers can make informed decisions and select the approach that best aligns with their production requirements, product specifications, and budget constraints.

Robotic system for THT assembly PCB board
Robotic system for THT assembly PCB board

Quality Control in THT PCB Assembly - Ensuring Reliability

Producing high-quality and reliable THT PCB assemblies requires stringent quality control measures at every stage of the manufacturing process. Overlooking even minor defects can lead to costly reworks, product failures, and potential safety hazards. Implementing robust quality control practices is crucial for maintaining product integrity and customer satisfaction. Let’s explore the key aspects of quality control in THT PCB assembly:

  1. Component Selection and Inspection
    The quality of THT assemblies begins with the selection of high-quality components from reputable suppliers. Upon receiving components, thorough incoming inspections should be conducted to identify any defects, damages, or deviations from specifications. This step helps ensure that only compliant components are used in the assembly process.
  2. PCB Preparation and Inspection
    Before component insertion, the PCBs themselves must undergo rigorous inspection to detect any defects, such as misaligned or missing drill holes, improper copper plating, or surface irregularities. Thorough PCB inspection can prevent issues that may arise during assembly or component insertion.
  3. Process Control and Monitoring
    Effective process control and monitoring ensure consistent quality in THT assembly. Key parameters such as soldering temperatures, wave heights, conveyor speeds, and flux application must be carefully monitored and adjusted as needed to maintain optimal conditions throughout the assembly process.
  4. Soldering Quality Inspection
    After the soldering process, inspecting the quality of solder joints for visual and functional defects is crucial. Visual inspections can identify issues such as insufficient solder, bridging, or poor wetting, while functional tests can detect potential electrical faults or intermittent connections.
  5. Advanced Inspection Techniques
    In addition to visual inspections, advanced inspection techniques like X-ray inspection (AXI) or automated optical inspection (AOI) can be employed to detect hidden defects or anomalies that may not be visible to the naked eye. These techniques are particularly valuable for identifying issues like cold solder joints, component misalignment, or solder voids.
  6. Environmental and Functional Testing
    Before final shipment, assembled PCBs may undergo environmental stress testing, such as thermal cycling or vibration testing, to ensure they can withstand harsh operating conditions. Functional tests are also conducted to verify that the assembled product meets all performance and operational specifications.
  7. Continuous Improvement and Corrective Actions
    Quality control in THT assembly is an ongoing process. Manufacturers should continuously analyze data from inspection and testing to identify areas for improvement, implement corrective actions, and update procedures or processes as needed to enhance product quality and reduce defect rates.

By implementing a comprehensive quality control strategy that encompasses every stage of the THT assembly process, manufacturers can ensure the production of high-quality, reliable products that meet customer expectations and regulatory standards.

Robotic vision sensor camera system for soldering and assembly PCB board
Robotic vision sensor camera system for soldering and assembly PCB board

THT vs SMT: Application Scenarios and Hybrid Assemblies

While SMT has become the predominant choice for modern electronics manufacturing, THT plays a vital role in specific applications and product designs. Understanding the strengths and weaknesses of each assembly method is crucial for selecting the appropriate technique based on project requirements. Additionally, many contemporary products leverage the benefits of both technologies through hybrid assemblies.

THT Assembly Applications:

  1. High-Power Devices: THT excels in accommodating large, high-power components such as transformers, heat sinks, and power transistors, which can dissipate heat more effectively through their protruding leads.
  2. Electromechanical Components: Devices like switches, relays, and connectors with sizeable lead configurations are often best suited for THT assembly, providing a robust mechanical connection to the PCB.
  3. Legacy Products: Existing product lines or designs that have historically used THT may continue to employ this technique to maintain compatibility and minimize redesign efforts.
  4. Prototyping and Low-Volume Production: For low-volume runs or prototype development, manual THT assembly can be a cost-effective solution, offering flexibility and ease of modifications.

SMT Assembly Applications:

  1. High-Density Designs: SMT enables the placement of a large number of components in a compact area, making it ideal for high-density designs like smartphones, tablets, and other miniaturized electronics.
  2. Portability and Weight Considerations: The smaller form factor and lightweight nature of SMT components make them suitable for portable and wearable devices where size and weight are critical factors.
  3. High-Volume Manufacturing: Highly automated SMT assembly lines offer unparalleled production efficiency and consistency, making them the preferred choice for high-volume consumer electronics manufacturing.
  4. Advanced Packaging: SMT accommodates modern packaging technologies like ball grid arrays (BGAs) and chip-scale packages (CSPs), enabling advanced functionality and miniaturization.

Hybrid Assemblies: The Best of Both Worlds

Many modern electronic products incorporate both THT and SMT components, leveraging the strengths of each assembly method in a hybrid approach. This mixed technology allows for design flexibility, accommodating various component sizes and types while optimizing performance, cost, and manufacturability.

In hybrid assemblies, SMT components are typically mounted first, followed by the insertion and soldering of through-hole components. Specialized soldering techniques like selective soldering or wave soldering with adapted pallet designs are employed to prevent damage to the SMT components during the THT soldering process.

By understanding the application scenarios and capabilities of THT and SMT assembly techniques, manufacturers can make informed decisions and choose the most appropriate approach, or a combination thereof, to meet their product requirements, production volumes, and operational constraints.

DIP Components

Future Trends and Developments in THT PCB Assembly

While SMT has gained significant traction in recent years, THT PCB assembly continues to evolve and adapt to meet the changing needs of the electronics industry. As new applications and product requirements emerge, the THT assembly landscape is poised for further advancements and innovations. Let’s explore some of the key future trends and developments shaping the world of THT PCB assembly.

  1. Increased Automation and Robotics
    To improve efficiency, consistency, and throughput, manufacturers are increasingly adopting automation and robotics in THT assembly processes. Automated component insertion machines, robotic soldering systems, and advanced inspection techniques are being integrated into production lines, minimizing manual intervention and reducing the potential for human errors.
  2. Integration with Industry 4.0 and Smart Manufacturing
    THT assembly is embracing the principles of Industry 4.0 and smart manufacturing, leveraging technologies like the Internet of Things (IoT), big data analytics, and machine learning. Real-time monitoring of production processes, predictive maintenance, and data-driven process optimization are becoming more prevalent, leading to improved quality, productivity, and cost-effectiveness.
  3. Advanced Soldering Techniques
    Advancements in soldering technologies are paving the way for more efficient and reliable THT assemblies. Techniques like laser soldering, which offers precise heat application and minimizes thermal stress on components, are gaining traction. Additionally, the development of lead-free solders and flux formulations is enhancing environmental sustainability and product safety.
  4. Hybrid Assembly Advancements
    As the demand for mixed-technology assemblies continues to grow, the integration of THT and SMT processes is becoming more seamless. Specialized soldering equipment, like selective soldering machines, are evolving to handle complex hybrid designs with greater precision and efficiency, minimizing the risk of damage to sensitive components.
  5. Miniaturization and High-Density THT Components
    While SMT dominates the high-density electronics landscape, there is a growing demand for miniaturized and high-density through-hole components. Component manufacturers are developing smaller form factors and innovative packaging solutions to meet the evolving needs of compact and high-performance electronic devices.
  6. Additive Manufacturing and 3D Printing
    The advent of additive manufacturing and 3D printing technologies is opening new possibilities for THT PCB assembly. The ability to create custom components, fixtures, and even PCBs with complex geometries and embedded features could revolutionize the way THT assemblies are designed and produced.
  7. Emphasis on Sustainability and Eco-Friendly Practices
    As environmental concerns continue to shape the electronics industry, THT assembly processes are focusing on sustainability and eco-friendly practices. This includes the adoption of lead-free soldering materials, energy-efficient manufacturing techniques, and responsible waste management practices to minimize the environmental impact of THT assemblies.

By embracing these future trends and developments, the THT PCB assembly industry is poised to remain a vital component of the electronics manufacturing ecosystem, offering unique capabilities and solutions to meet the ever-evolving demands of diverse applications and product requirements.


THT PCB assembly, despite its long-standing history, remains an indispensable technique in the world of electronics manufacturing. While SMT has gained widespread popularity, THT continues to offer unique advantages, particularly for applications requiring large components, high power handling, and robust mechanical connections.

In this comprehensive guide, we have explored the intricacies of THT PCB assembly, from the assembly process and common techniques to quality control measures and future trends. Whether you’re a hobbyist, an engineer, or a manufacturing professional, understanding the nuances of THT assembly is crucial for making informed decisions and producing high-quality, reliable electronic products.

As the industry continues to evolve, embracing advancements in automation, hybrid assemblies, and sustainable practices will be key to unlocking the full potential of THT PCB assembly. By staying ahead of the curve and adopting cutting-edge technologies and techniques, manufacturers can leverage the strengths of THT to meet the ever-changing demands of the electronics market.

JHYPCB: Your Trusted Partner in PCB Manufacturing

At JHYPCB, a leading Chinese PCB manufacturer, we understand the importance of both THT and SMT assembly techniques. Our expertise spans a wide range of PCB manufacturing services, including SMT, THT, and mixed technology assemblies, catering to diverse industry needs.

With state-of-the-art facilities, stringent quality control measures, and a team of experienced professionals, we are committed to delivering high-quality PCB assemblies that meet and exceed our customers’ expectations.

Partner with JHYPCB for Your THT PCB Assembly Needs

If you’re in need of reliable and high-quality THT PCB assembly services, look no further than JHYPCB. Our team of experts is ready to assist you with your project requirements, from prototyping to large-scale production runs.

Contact us today to discuss your specific needs, and let us be your trusted partner in delivering exceptional THT PCB assemblies that drive innovation and success in your industry.

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JHYPCB is a leading PCB prototyping, PCB manufacturing and assembly service provider in China, offering quick turn PCB prototyping, multi-layer PCB manufacturing and turnkey PCB assembly services.

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