July 5, 2024

What is Through-Hole Technology (THT) in PCB

Printed Circuit Boards (PCBs) are the backbone of modern electronics. They provide a platform for connecting electronic components and creating functional circuits. There are two main methods for assembling components on PCBs: Through-Hole Technology (THT) and Surface Mount Technology (SMT).

Despite the prevalence of SMT, THT remains vital in many areas. THT is often used in products that need high reliability and mechanical strength. For instance, aerospace and military electronics rely on THT for its robust connections.

THT offers a significant advantage in industries where maintenance and repair are standard. Components can be easily replaced or modified, ensuring long-term functionality and reliability.

In summary, Through-Hole Technology is not just a relic of the past. It plays a critical role in modern electronics, offering reliability, durability, and simplicity that SMT cannot always provide.

PCB with through-hole components and surface-mount chips

What is Through-Hole Technology (THT)?

Through-hole technology (THT) is a method for mounting electronic components on a printed circuit board (PCB). Components in THT have leads, or pins, that go through holes drilled into the PCB. 

These leads are soldered to pads on the opposite side, creating a secure mechanical and electrical connection. THT components are known for their reliability and durability, making them ideal for various applications.

For more on the basics of PCB assembly, visit Basic Things You Should Know About PCB Assembly Process.

Historical Context and Development of THT

THT has been a cornerstone of electronic assembly since the mid-20th century. Before its development, circuits were often wired by hand, which was labor-intensive and prone to errors. THT revolutionized the industry by allowing for more consistent and reliable connections.

In the early days, THT was the primary method for mounting components. It enabled the mass production of electronic devices, significantly reducing costs and improving performance. 

Over the years, THT components have evolved, with improvements in materials and manufacturing techniques enhancing their reliability and ease of use.

Despite the advent of newer technologies, THT remains essential in various applications. Its development paved the way for modern electronics, providing a foundation for new methods.

Comparison with Surface Mount Technology (SMT)

While THT involves inserting leads through holes in the PCB, Surface-Mount Technology (SMT) places components directly onto the board's surface. 

SMT has become popular because it allows for smaller and more compact designs. Components can be placed on both sides of the PCB, and the assembly process is faster and more efficient.

However, THT has several advantages over SMT. THT connections are typically more robust and reliable, making them suitable for environments with high mechanical stress or extreme temperatures. For example, aerospace and military applications often prefer THT for its robustness.

Additionally, THT is easier to work with for manual assembly and prototyping. Components are more prominent and easier to handle, which is beneficial for educational purposes and hobbyist projects.

In summary, both THT and SMT have their unique advantages. THT excels in reliability and ease of use, while SMT is preferred for its efficiency and ability to produce smaller, more complex devices. Understanding both technologies is crucial for selecting the proper method for each application.

Person-soldering-a-green-PCB-using-through-hole-technology

Types of THT Components

Through-hole technology (THT) involves various components with specific functions and characteristics. Understanding these components helps in designing and assembling reliable and efficient electronic circuits. For a detailed look at PCB components, check out Commonly Used PCB Components and Functions.

Electronic Components

Resistors

Resistors are among the most common THT components. They control the flow of electrical current in a circuit by providing a specific amount of resistance. Doing so helps manage the voltage and current levels, ensuring the circuit functions correctly. Learn more How to Read a Resistor on PCBs?

Capacitors

Capacitors store and release electrical energy. They are essential for filtering, smoothing, and timing applications in circuits. THT capacitors are available in various types, such as electrolytic and ceramic, each suited for different purposes.

Inductors

Inductors store energy in a magnetic field when electrical current flows through them. They are used in filtering and tuning circuits, helping to manage signal frequencies and reduce noise.

Diodes

Diodes allow current to flow in only one direction. They are crucial for rectification, which converts alternating current (AC) to direct current (DC). THT diodes are reliable and easy to incorporate into various circuits.

Integrated Circuits (ICs)

Integrated Circuits (ICs) are complex components that can contain hundreds or thousands of individual electronic elements. They perform various functions, from simple logic operations to complex signal processing.

Dual In-line Packages (DIP)

DIP is a popular packaging style for ICs in THT. These packages have two parallel rows of pins inserted into the PCB holes. They are easy to handle and solder, making them ideal for prototyping and educational projects.

Other Common IC Packages

Other THT IC packages besides DIP include SIP (Single In-line Package) and ZIP (Zigzag In-line Package). These packages offer different pin configurations and sizes to suit various applications.

Modules

Modules are larger assemblies that incorporate multiple components into a single package. They simplify circuit design and assembly by combining several functions into one unit.

LED Displays

LED displays are used for visual output in many devices. They can show numbers, characters, and graphics. THT LED displays are robust and easy to integrate into projects, from simple indicators to complex displays.

Power Modules

Power modules manage and distribute power within a circuit. They can include components like voltage regulators, transformers, and rectifiers. THT power modules are essential for ensuring stable and reliable power delivery.

Other Large Component Assemblies

Other THT modules include relay modules, sensor modules, and communication modules. These assemblies combine various components to perform specific tasks, making them convenient for complex circuit designs.

Understanding these THT components helps you select the correct parts for your projects. Whether you're working on a simple hobby project or a complex industrial system, THT components offer reliability and ease of use.

Diagram-of-a-through-hole-assembly-with-component-leads

Assembly Methods in THT

Through-hole technology (THT) components can be assembled onto printed circuit boards (PCBs) using different methods. The two primary methods are manual soldering and wave soldering. Each has its processes, applications, and advantages.

Manual Soldering

Process Description

Manual soldering is a straightforward and hands-on method for assembling THT components. Here's how it works:

  1. Component Placement: First, place the THT components into the pre-drilled holes on the PCB.
  2. Soldering: Heat the component leads and pads on the PCB with a soldering iron. Apply solder to form a connection. The solder melts and bonds the component lead and the pad.
  3. Inspection: Check the solder joints to ensure they are smooth and shiny. This indicates a good connection.

Applications and Advantages

Manual soldering is ideal for:

  • Prototyping: Perfect for creating and testing new circuit designs.
  • Small Batch Production: Useful for low-volume manufacturing where automated processes are not cost-effective.
  • Repairs and Modifications: Allows easy removal and replacement of components.

Advantages of manual soldering include:

  • Flexibility: Easy to make changes and adjustments.
  • Low Cost: Requires minimal equipment.
  • Accessibility: Ideal for hobbyists, educators, and small-scale manufacturers.

Wave Soldering

Process Description

Wave soldering is an automated process designed for high-volume production. Here's how it works:

  1. Preparation: Components are placed into the PCB holes, either manually or by a machine.
  2. Flux Application: The PCB is coated with flux to clean and prepare the surfaces for soldering.
  3. Preheating: The PCB is heated to prepare for soldering.
  4. Solder Wave: The PCB passes over a wave of molten solder. The solder adheres to the exposed metal surfaces, connecting the component leads and the PCB pads.
  5. Cooling: The PCB is cooled to solidify the solder joints.

Applications and Advantages

Wave soldering is best for:

  • Mass Production: Efficiently handles large volumes of PCBs.
  • Consistent Quality: Ensures uniform and reliable solder joints.
  • Complex Assemblies: Can manage boards with numerous THT components.

Advantages of wave soldering include:

  • Efficiency: Processes many PCBs quickly.
  • Reliability: Produces consistent, high-quality solder joints.
  • Scalability: Suitable for scaling up production.

Both manual soldering and wave soldering are used in THT assembly. The correct method is chosen based on the project requirements, including volume, complexity, and budget. 

Each method ensures that THT components are securely and reliably attached to PCBs, ready for their intended applications.

Close-up-of-a-green-PCB-with-various-electronic-parts

Advantages of Through-Hole Technology

Through-hole technology (THT) offers several advantages, making it a preferred choice in various applications. These benefits include durability, reliability, and ease of use, making THT components versatile and dependable.

Durability

Mechanical Strength

One of THT's main advantages is its exceptional mechanical strength. The leads of THT components pass through the PCB and are soldered on the other side, creating robust connections. 

This physical bond makes THT components highly resistant to mechanical stress, such as vibrations and physical shocks. This strength is significant in applications where the device may be subjected to rough handling or harsh conditions.

Suitability for Harsh Environments

THT components are well-suited for environments with extreme conditions. They can withstand high temperatures, humidity, and other challenging factors without compromising performance. This makes THT an ideal choice for aerospace, military, and industrial applications, where durability and reliability are crucial.

For more on durable PCBs, explore Benefits and Applications of High-Volume PCB.

Reliability

High Reliability for Critical Applications

THT components are known for their high reliability. The secure connections formed by soldering the leads through the PCB ensure that the components remain firmly in place. This reliability is vital for critical applications where failure is not an option. 

For example, in medical devices and safety systems, the robust connections provided by THT components help ensure consistent and dependable performance.

Ease of Use

Simple Assembly Process

The assembly process for THT components is straightforward. Placing the leads through the holes and soldering them is simple and intuitive. This simplicity makes THT an excellent choice for various users, from hobbyists to professionals. 

It requires minimal training and equipment, making it accessible for anyone interested in building or repairing electronic circuits.

Ideal for Prototyping and Educational Purposes

THT is particularly beneficial for prototyping and educational purposes. The larger size of THT components makes them easier to handle and work with. This ease of use is valuable for beginners learning about electronics. 

Students can easily see and understand the connections, which helps them grasp circuit design fundamentals. Additionally, THT allows quick and easy modifications for prototyping, enabling designers to test and refine their circuits effectively.

Close-up-of-a-green-PCB-with-resistors-and-components

Applications of Through-Hole Technology

Due to its unique advantages, through-hole technology (THT) is used across various fields. It excels in applications where reliability, durability, and ease of handling are essential.

Aerospace and Military

Reliability and durability are paramount in aerospace and military applications. Equipment in these fields must perform flawlessly under extreme conditions. 

THT components are chosen for their robust mechanical connections, which can withstand high vibrations, shocks, and temperature variations. 

For instance, in avionics systems and defense equipment, THT ensures that electronic connections remain intact and functional over long periods, even in harsh environments. This reliability is critical for the safety and effectiveness of aerospace and military operations.

Industrial Equipment

Industrial environments demand robust and maintainable systems. Machinery and equipment often face rigorous usage, requiring components that can endure heavy-duty operations. 

THT components are ideal for such settings because of their physical solid connections and high resistance to mechanical stress. THT components are used in control systems, power supplies, and heavy machinery in factories and industrial plants. 

Their durability reduces the need for frequent repairs, ensuring continuous operation and minimizing downtime. Additionally, the ease of replacing THT components makes maintenance straightforward and cost-effective.

For industrial applications, refer to Industrial Automation PCB Assembly.

Educational and Hobby Projects

THT is a favorite in educational and hobbyist projects due to its ease of handling and prototyping capabilities. For students and hobbyists, THT components are more prominent and easier to manipulate, making the learning process more accessible. 

THT helps students understand basic electronic principles through hands-on experience in educational settings. Projects like building simple circuits, learning to solder, and experimenting with different components become more manageable with THT.

For hobbyists, THT is perfect for creating custom electronic projects. Its straightforward assembly process allows for quick prototyping and easy modifications, enabling creators to bring their ideas to life efficiently.

Comparison-of-through-hole-PCB-vs-SMT-PCB

THT vs. SMT

Through-Hole Technology (THT) and Surface Mount Technology (SMT) are two primary methods for assembling electronic components on printed circuit boards (PCBs). 

Each has its advantages and is suitable for different applications. Understanding the differences can help you choose the right technology for your project.

Size and Weight

Comparison of Component Size and Weight

One of the most significant differences between THT and SMT is the size and weight of the components.

  • THT Components

THT components are generally larger and heavier because they have long leads that pass through the PCB. This makes them easy to handle and ideal for applications where size is not a constraint.

  • SMT Components

SMT components are much smaller and lighter. They are mounted directly onto the surface of the PCB without the need for holes, allowing for more compact and lightweight designs, which is crucial for modern, high-density electronic devices like smartphones, laptops, and wearable tech.

Assembly Complexity

Differences in Assembly Techniques and Equipment

The assembly process for THT and SMT components also varies significantly.

  • THT Assembly

THT assembly can be done manually or through automated wave soldering. Manual assembly is straightforward and doesn't require sophisticated equipment, making it accessible for small-scale production and prototyping. 

Wave soldering, used for larger volumes, involves passing the PCB over a wave of molten solder to attach the components. This process is more straightforward than SMT but less efficient for tiny components.

  • SMT Assembly

SMT assembly is more complex and requires advanced machinery like pick-and-place machines, reflow ovens, and inspection systems. Components are placed on the PCB surface and soldered using a reflow process. 

This method is highly efficient for mass production and allows components to be placed on both sides of the PCB. However, the initial setup cost and equipment are more expensive, making it less suitable for low-volume production.

Suitability for Different Applications

When to Choose THT Over SMT and Vice Versa

Choosing between THT and SMT depends on the specific requirements of your project.

  • Choose THT When:

Durability is Crucial: THT is ideal for applications that require mechanical solid bonds, such as aerospace, military, and industrial equipment.

Ease of Repair: THT components are more accessible to replace and repair, making them suitable for prototypes, educational projects, and maintenance-heavy applications.

High Power Requirements: THT is better suited for handling high-power and high-voltage components due to its robust connections.

  • Choose SMT When:

Space is Limited: SMT is perfect for compact and lightweight designs, which are essential in consumer electronics like smartphones and tablets.

High Volume Production: SMT's automated assembly process is highly efficient for large-scale production, reducing costs and time.

High-Frequency Applications: SMT components have shorter leads, which can reduce inductance and resistance, making them suitable for high-frequency applications.

Person-inspecting-a-green-PCB-with-through-hole-leads

Conclusion

Through-hole technology (THT) continues to play a crucial role in electronics. Its importance and applications span various industries, highlighting its enduring value and versatility.

THT is a fundamental method for assembling electronic components on printed circuit boards (PCBs). It is celebrated for its durability, making it the go-to choice for applications that require mechanical solid bonds and high reliability. 

The ease of handling and assembly makes THT perfect for educational purposes and hobbyist projects, allowing beginners to learn and experiment with electronics effortlessly.

In conclusion, Through-Hole Technology remains a cornerstone of PCB assembly, offering unmatched durability, reliability, and ease of use. 

Its continued relevance in various industries underscores its importance, ensuring that THT will remain a critical component of electronic assembly for years.

Article written by Alice Lee