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Through-Hole Technology in PCB Design

Through-hole technology in PCB design plays a crucial role in electronics. Ever wondered how your device components securely connect to the circuit board for flawless operation? THT has a long history, with manufacturers anchoring components onto PCBs through holes, ensuring robust connections.

Surface-mount technology (SMT) has become popular for its miniaturization benefits. However, Through-Hole Technology (THT) remains crucial for specific applications in the evolving electronics industry. This article will cover THT basics and its role in modern PCB design.

Introduction to Through-Hole Technology (THT)

Origins of Through-Hole Technology

 A circuit board with a 7-segment display, LEDs, IC socket, and a breadboard area.
  • Through-hole technology dates back to the earlier days of electronics when manually soldering components was the norm. This method provided a reliable connection between the component and the circuit board.
  • As technology progressed, the need for a systematic approach for attaching electronic components led to the development of THT.

Basic Procedure

  • Drilling: Drilling specific locations on the PCB to create holes precedes component insertion. These holes align with the leads of the electronic components intended for insertion.
  • Component Insertion: The leads of THT components are then manually or mechanically inserted through these pre-drilled holes.
  • Soldering: After placing the components, manufacturers solder them on the opposite side of the board. The smaller components allow for more compact and densely packed PCB designs.

Contrast with SMT

 A close-up of a microchip on a surface mount technology (SMT) circuit board.
  • Surface Mounting: Unlike THT, surface mount technology (SMT) does not involve drilling holes. Instead, components are directly placed and soldered onto the surface of the PCB.
  • Miniaturization: SMT has become predominant in modern electronics due to the shift towards miniaturization. The components are smaller, allowing for more compact and densely packed PCB designs.

Applications of Through-Hole Technology

  • Rugged Environments: People often opt for THT in environments characterized by mechanical stress or vibrations. This preference is because of the strong bond it creates between the component and the PCB.
  • Prototyping: THT components are frequently more manageable for those designing prototypes or pursuing DIY electronics projects. Additionally, they are simpler to solder manually.

Understanding THT’s fundamental characteristics and applications makes one appreciate its unique role in electronics design. This remains true as newer technologies, like SMT, continue to evolve.

Benefits of Through-Hole Technology in PCB Design

Mechanical Strength

A detailed view of a green printed circuit board (PCB) showcasing multiple black rectangular components and an orange resistor. The components' leads are inserted through drilled holes in the board and soldered on the opposite side, highlighting the robust mechanical connection achieved through Through-Hole Technology (THT), which offers enhanced resistance to mechanical forces compared to surface-soldered connections.
  • Robust Connections: Inserting leads through drilled holes is part of the process. Soldering them in place creates a solid mechanical connection. This bond is inherently more rigid and resistant to mechanical forces than surface-soldered connections.
  • Ideal for Stressed Components: Components such as connectors, which may undergo frequent plugging and unplugging, benefit significantly from the robustness of THT mounting. Similarly, large capacitors, prone to mechanical stress because of their weight or size, also benefit from this strength.
  • Vibration Resistance: The mechanical strength of THT components provides added assurance in environments susceptible to vibrations or sudden impacts, such as industrial or automotive applications. It helps prevent component displacement in such conditions.

Ease of Prototyping

  • Hobbyist-friendly: Beginners and hobbyists often find THT components easy to use in electronics. Their larger size and the nature of their connection make them more forgiving for newcomers.
  • Manual Soldering: Designers incorporate protruding leads into THT components to facilitate manual soldering. These leads provide a larger area for solder to flow and bond.
  • Component Adjustments: Mistakes happen, especially in prototyping. THT components can be more easily de-soldered and repositioned than their SMT counterparts, simplifying design iterations.

High Power Handling

Close-up view of a brown printed circuit board (PCB) featuring various Through-Hole Technology (THT) components like blue capacitors and multi-colored resistors. The leads of these components are inserted through the PCB, emphasizing their ability to effectively dissipate heat and prevent potential overheating.
  • Thermal Dissipation: Mistakes happen, especially in prototyping. THT components can be more easily de-soldered and repositioned than their SMT counterparts, simplifying design iterations.
  • Applications: This benefits power components such as large resistors, transistors, or voltage regulators. They often generate significant heat during operation.
  • Safety: Efficient heat dissipation ensures the component’s longevity. It also prevents potential overheating, enhancing the electronic system’s safety.

Longevity and Reliability

  • Durable Solder Joints: THT solder joints offer enhanced durability. This is because they have a larger volume and a through-board design, distinguishing them from surface-mounted joints.
  • Environmental Resistance: THT components are generally more resistant to environmental stresses, such as changes in temperature or humidity. This resilience translates to more extended component and board lifetimes in challenging conditions.
  • Maintenance: Because of their robust nature, THT components typically require less frequent maintenance or replacement in the long run. Their sturdy connections contribute to this longevity.

In summary, despite the rapid miniaturization of SMT making THT seem dated, it possesses unique advantages. It remains indispensable in various applications and scenarios.

Challenges of Through-Hole Technology

Real Estate Consumption

 Diagram illustrating the structure of a Through-Hole Technology (THT) component on a printed circuit board (PCB). The component is shown mounted on the "Component Side" with its leads passing through the PCB and extending to the "Solder Side." Labeled elements include the component, PCB, pad, and lead. The diagram highlights the space consumed by THT components on both sides of the PCB.
  • Larger Footprint: The intrinsic design of THT components involves leads meant to pass through the PCB. This design inherently requires more space. This contrasts with SMT components, which designers intentionally design to lie flat on the PCB’s surface.
  • Design Constraints: The bulkier size of THT components can limit PCB layout optimization. This is especially true for compact or densely packed designs.
  • Miniaturization Limitations: As the electronics industry continues its relentless march towards miniaturization, the larger footprint of THT becomes a clear drawback. Smartphones, wearables, and many IoT devices require highly compact internal designs. These designs often make them incompatible with THT due to space constraints.

Automated Manufacturing Constraints

Illustration of an automated manufacturing line consisting of interconnected machines equipped with indicator lights. The machines are designed for optimal placement of electronic components. The image underscores the challenges of integrating bulkier Through-Hole Technology (THT) components, which may require slowing down the assembly line for precise alignment and placement.
  • Machine Optimization: Automated manufacturing lines, especially pick-and-place machines, primarily optimize for SMT components. These machines efficiently place small SMT components on boards. However, THT components complicate the process because of their bulkier nature and the necessity for hole alignment.
  • Slower Assembly Line: Using THT components in automated lines slows the entire assembly process. This slowdown can lead to reduced manufacturing throughput.
  • Increased Costs: Handling THT components in automated lines can be slower and more complex, leading to higher manufacturing costs. This is especially noticeable when compared to fully SMT-based assembly processes.

Limited Component Availability

  • Shift Toward SMT: Manufacturers are increasingly producing components primarily in SMT packages. The industry’s apparent preference for SMT drives this choice because of its compatibility with miniaturization and automation.
  • Reduced THT Options: As a result, designers may encounter fewer component options in THT packages. This limitation could restrict their design choices or compel them to seek alternatives.
  • Legacy Designs: This trend is incredibly challenging for maintaining or updating legacy designs that heavily rely on THT components. Finding exact replacements or equivalents can become a daunting task.

THT offers undeniable benefits in specific applications. Designers and manufacturers must be aware of these challenges. Balancing the strengths and limitations of THT against project requirements is crucial to achieving optimal design and manufacturing outcomes.

PCB Design Considerations for Through-Hole Technology

Hole Sizing

  • Precision is Key: The accuracy of hole sizes in the PCB directly impacts the efficiency of the soldering process. Too small or large holes can lead to weak solder joints or component damage.
  • Lead Diameter Match: Designers must ensure that the drilled hole sizes closely match the lead diameters of the THT components. This guarantees a snug fit, ensuring optimal solder flow and a solid mechanical bond.

Annular Ring

Close-up of a printed circuit board (PCB) highlighting a drilled hole surrounded by an annular ring. Annotations detail the various components: "Finished Hole (drilled and copper plated)", "Annular Ring", and "Copper Plated". The image offers a detailed view of the construction and terminology associated with PCB through-hole design.
  • Function: The annular ring is the copper area surrounding the drilled hole. It provides a surface for the solder to bond, connecting the component lead to the PCB’s circuitry.
  • Size Matters: A correctly sized annular ring ensures enough surface area. This allows the solder to form a robust and electrically reliable connection. An annular ring that is too small might result in weak solder joints, while one that’s too large can waste precious PCB real estate.

Solder Mask Clearance

  • Protection and Precision: The solder mask is a protective layer. Its purpose is to prevent solder from bonding to unintended areas of the PCB. Ensuring this mask does not overlap with the annular rings intended for soldering is paramount.
  • Avoiding Bridging: Proper clearance between the solder mask and the annular ring prevents issues such as solder bridging. This ensures clean and individual solder joints.

Component Placement

  • Spatial Planning: Strategic placement is crucial because of the larger size of THT components. This optimization ensures that components don’t interfere with each other and maximizes the use of space.
  • Multi-layer Considerations: In multi-layer PCBs, designers must be aware of components on both sides to avoid accidental overlaps or interference.

Thermal Considerations

  • Dissipating Heat: THT components, especially power components, can generate significant heat. These components often require broader thermal pathways or “reliefs” to dissipate this heat efficiently.
  • Thermal Design: Ensuring proper thermal relief pathways helps maintain component health and prevent potential heat-related failures. This may involve heat sinks, vias, or specific copper areas for heat dissipation.

Routing and Signal Integrity

  • Navigating Complexity: THT components introduce additional routing challenges because of their size and the space they occupy. Managing trace paths efficiently becomes vital.
  • Maintaining Signal Quality: To ensure optimal performance, especially in high-frequency applications, it’s crucial to keep signal paths short. Additionally, maintaining impedance control is essential for achieving the desired performance. This minimizes signal degradation and interference.

Incorporating THT components into a PCB design requires a nuanced understanding of these considerations. While it presents unique challenges, careful planning can lead to efficient PCB designs. Adherence to best practices is essential for achieving reliability in these designs.


Through-hole technology in PCB design remains essential to the electronics world, especially in specific niches and applications. While surface-mount technology offers miniaturization and speed advantages, THT provides robustness and reliability. As with many things in engineering, the choice between THT and SMT boils down to the project’s specific requirements. Both have their place, and a holistic understanding of their strengths and weaknesses ensures optimal PCB design.

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