Through-Hole Technology PCB Assembly

Through-hole technology PCB Assembly means that component leads are placed into the holes drilled through the PCB, then soldered to mount them in positions on the other side of the board. It is ideal for high-stress applications because it can produce robust mechanical bonds and reliable electrical connections. Surface Mount Technology (SMT) is leading in miniaturized electronics, but THT is still indispensable in many applications.
FC is the best PCB Assembly company in China. We not only supply excellent SMT Service but also offer the most top-tier THT Assembly Service. So it’s a great idea to choose FC to work with you!

What is Through-hole technology PCB Assembly

Through-hole technology assembly, THT Assembly, is a mounting method for electronic components. It includes using component pins to insert components into existing holes in printed circuit boards (PCBs) and soft brazing of electronic components by hand assembly or automatic insertion loaders.
THT works on a simple but effective principle. First, holes are pre-drilled in the PCB to match the component pin diameters. Then, the component pins are inserted into these holes. Finally, the component pins are connected to the pads on the PCB by soldering on the bottom or the other side of the PCB. This soldering process can be performed using various methods, including manual and wave soldering.

Parts Involved in THT Assembly

THT components include connectors, rectifiers, wire terminals, inductors, resistors, capacitors, and larger integrated circuits. These components are recognized by the leads or pins intended to go through the holes in the PCB. Through-hole components are a must in electronic circuits because they provide and meet the capacity to process, control, and regulate electrical impulses. These components are generally divided into passive and active components. The unique properties of each kind, in the context of other elements of the rest of the technology components, also achieve certain tasks. As well as in other parts of the technologies component itself, to increase the overall workability and performance of the circuit.

Passive THT PCB Components

  • Axial Components
Because their leads can come from both ends, they can be mounted horizontally on the PCB. This arrangement effectively utilizes the space on a board and can be helpful on layouts with limited vertical space. Axial components are commonly used for resistance and rectification in circuits. Examples include resistors, diodes, and certain capacitors, axial components.
  • Radial Components
On the other hand, radial components have leads protruding from one side of the board, so the mounting direction is free. If space is important, and you want to save space, radial components take up more of the board area than axial components. Radial components are commonly found in capacitors, LEDs, and some inductors.

Active THT PCB Components

Transistors amplify and modulate signals. By using these basic semiconductor devices for purposes related to voltage regulation, digital logic circuits, and audio amplification, current flows from one terminal to another in a control system.
Integrated Circuits (ICs)
They are small, flexible semiconductor devices that house numerous electrical elements, including capacitors, resistors, and transistors, among several others, bunched into one chip. The small, flexible devices can be found in widespread use across many application areas in signal processing, memory storage, and microprocessor control. Their deployment in many package forms, such as through-hole layouts, renders them applicable for a broad spectrum of application areas within computing and electronics.
Power Regulators
Power regulators are electronic components that are produced to control and direct the voltage and current driving a circuit. These contribute to the safe operation of any electronic equipment by regulating power supply voltages; they also protect other circuit components from overvoltage or overcurrent. Usually, through-hole power regulators are used in circuits such as voltage regulators, battery charging systems, and power supply circuits.

FC Main Steps in THT PCB Assembly

Through-hole (TH) technology inserts component leads into drilled holes on a printed circuit board (PCB) and then solders the leads to pads on the other side. This creates a permanent connection between the component and the board. The THT process for FC typically includes the following steps:

Step1: PCB Layout and Design

Hole Placement: These are designed very precisely. The placements should be equivalent to that of the lead positions of components.
Pad Design: Ensure pads are large enough to take the solder and form a robust mechanical bond.
Trace Routing: The tuning of trace pathways to reduce electrical interference and ensure signal integrity.

Step2: Component Insertion

Manually: Skilled operators can manually insert components. This method is appropriate for intricate or low-volume assemblies.
Automated Insertion: High-volume production is best suited for automated equipment that precisely and swiftly installs components.

Step3: Soldering Methodologies

Wave Soldering: The PCB moves on a wave of molten solder that adheres to exposed metal areas to fix the components. This is a great approach if you are looking to make a large production output.
Selective Soldering: Selective soldering is employed on boards with both SMT and THT components and allows for the solder to flow through certain areas without disturbing adjacent components.
Hand Soldering: Operators use soldering irons when fine control is required for small-scale manufacturing or rework jobs.

Step4: Inspection and Quality Control

Visual Inspection: Workers check to see if a cold joint, solder bridge, and proper positioning of components are in place.
Automated Optical Inspection (AOI): Systems that inspect the board for defects and check the consistency of the operations.
Testing Electrically: Verifying the board’s operation through functionality and In-Circuit testing (ICT).

Applications of THT PCB Assembly at FC

Besides consumer electronics, SMT, which is the industry’s standard in high-density PCBs, THT remains irreplaceable for durability and reliability in some sectors:
PCB Automotive


THT is also well known in automotive electronics such as engine control systems, body control systems, and infotainment systems.


THT components are used in telecommunications applications such as central office equipment.
industrial equipment

Manufacturing Equipment

The hefty connections made by THT are perfect for industrial control systems that must work under tough conditions and constant shaking.

Defense and Aerospace

Vital uses in which longevity and dependability are essential.
Medical machine

Medical Devices

High-reliability specifications demand that THT be used for specific components.
Industrial & Commercial -robotics, consumer electronics, UAVs, connectors and LED lighting applications

Power Electronics

Applications that require high current and voltage can make use of THT components' improved heat dissipation.

Future Outlook for THT PCB Assembly

Even with SMT‘s dominance, THT continued growing and was still relevant in some market applications.
Hybrid Assemblies: By combining THT and SMT, hybrid assemblies can take advantage of and maximize the benefits of each technology.
Innovative Materials and Soldering Methods: New materials and solutions will enhance the effectiveness and dependability of the THT assembly.
Niche Applications: THT will continue to serve niche markets where its unique benefits are unavoidable, as in industrial and military electronics that have been ruggedized.

Constraints with THT PCB Assembly

THT also has some constraints:
  • Low Component Density: THT components are larger and lower in density, which limits the total size and complexity of a printed circuit board
  • Higher Production Costs: Automation is necessary as more labor-intensive and manual labor makes it less suitable for mass production.
  • Less Automation: Manual insertion of through-hole components (THC) is less automated than surface mount technology (SMT), resulting in higher manufacturing costs and longer assembly times.
  • Weight and Space Restraints: Because THT components are typically heavier and larger than SMT components, their use in smaller devices is limited.
  • Manufacturing Complexity: The necessity of drilling holes and automated or human insertion might raise the cost and complexity of production.
  • Production Speed: THT assembly is usually slower than SMT assembly because it requires more processes.

Differences Between THT and SMT

Although SMT and THT are both techniques for assembling components into printed circuit boards, they differ significantly in a few important ways:

Component Size

Compared to their THT equivalents, SMT components are substantially smaller. A THT resistor has a size of 5-7mm, whereas an SMT resistor may only have 1-2mm. Due to the small size, more SMT components can be mounted on the same printed circuit board area.

PCB Density

Higher-density PCB assemblies with SMT are made possible by the small component size. On the PCB, components can be arranged very closely together with minimal wasted space. THT, on the other hand, needs enough room between holes to facilitate drilling and insertion.

Assembly Process

THT relies more on manual labor for soldering and insertion, whereas SMT assembly is automated utilizing pick-and-place equipment. SMT has a higher upfront cost, but it is faster to assemble.

Rework Ability

Replacing a defective part on a THT assembly is simpler if each part can be removed and replaced individually.SMT defects can only be mended by hot air soldering and specialized tools.


SMT is a good match for automation, which involves the use of special machines that can produce large quantities of PCBs fast. On the other hand, THT prototype builds are better suited for it because of its complicated nature.

Financial considerations

 The equipment used in SMT costs more compared to that used in THT. Nevertheless, SMT has reduced costs in mass production as it has faster assembly times and greater yield rates.
In summary, SMT enables complex and miniature PCB assembly but requires a higher level of skill and equipment. On the contrary, THT is easier to rework and is therefore suitable for simple and low-volume production.

Benefits of THT PCB Assembly at FC

Though THT components are more sizable and less high-watchable than SMT components, components made from them at FC yield the following advantages:

Mechanically Improved Strength

FC THT components can withstand physical stress since they are mounted through the board, making them very useful for industrial controls or aircraft equipment.


FC THT components are readily interchangeable, making troubleshooting and repairs easier. This is advantageous for prototypes and low-volume manufacturing runs.

Availability of Components

FC THT configurations are still the main source for those high-power components or need exact lead placement.

Easiest to Hand Assemble

FC THT is an excellent choice for hobbyists and low-volume manufacturing because it works well with manual soldering.

Straightforward Visual Inspection and Modification

Because THT components with large sizes and pins are directly accessible, they are simple to inspect for problems and easily replaced just with eyes.


FC THT is renowned for its repeatability due to its ruggedness and electrical and mechanical bonds that adhesive the parts to the PCB. Such bonds are critical for applications like medical and aerospace systems.


FC THT components are more durable and stronger against environmental conditions and physical stress

Ease of Prototyping and Testing

The stages of prototyping and testing are made easier by the easy insertion and removal of components.

Heat Dissipation

FC THT components are more suited for high-power applications because of their improved ability to dissipate heat through their leads.

Less Upfront Investment Needed for Specialized Equipment

Compared to SMT, THT requires less upfront investment for specialized equipment.


THT PCB assembly is a reliable and long-lasting method of manufacturing printed circuit boards, especially for low-density, simple boards. Nevertheless, THT remains a useful technology where reliability and ruggedness are important. Knowledge of the pros as well as cons of THT empowers manufacturers and designers to choose the best assembly technique that suits their specific needs.
THT won’t disappear soon. Technical advancements like automated THT placement and miniaturization of THT components will maintain their significance as manufacturers explore how SMT and THT can be integrated on a single PCB (mixed assembly) for optimum results. With its unique advantages and long-term applications, THT is likely to remain an integral part of electronics manufacturing in years to come. Although SMT dominates mainstream electronic production today, it still maintains its durability, dependability, and appropriateness for high-stress applications. By understanding and optimizing through-hole procedures, manufacturers can build robust, high-quality electronic systems that meet strict requirements in specialized areas. The evolution of technology will further enhance the capabilities of THTs through their integration with modern manufacturing processes, hence securing their position in man

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