Through-Hole (TH) Technology: An Ultimate Guide

What is Through-Hole Technology?

Through-Hole Technology (THT) involves mounting electronic components onto a PCB by inserting their leads through drilled holes and soldering them to pads on the opposite side. This method, which predates SMT, was the industry standard until the 1980s. While SMT now dominates mass production, THT retains critical importance in sectors where robustness and longevity are non-negotiable.

A Brief History of Through-Hole Technology

THT emerged in the 1950s with the rise of consumer electronics. Early PCBs relied on manual component insertion and hand soldering. The introduction of automated axial inserters and wave soldering in the 1970s streamlined production, making THT the backbone of electronics manufacturing for decades. Though SMT’s efficiency eventually overshadowed THT for small, high-volume devices, through-hole components remain indispensable in industries like aerospace, automotive, and industrial machinery.

Through-Hole Components: Design and Characteristics

TH components are distinguishable by their wire leads, which are inserted into pre-drilled PCB holes. Common examples include:

Passive Components: Resistors, capacitors, and inductors with axial or radial leads.
Connectors and Headers: Used for board-to-board or cable connections.
Electromechanical Parts: Relays, switches, and transformers.
High-Power Devices: Voltage regulators and heat-sinked semiconductors.

These components are typically larger than SMDs, with leads that withstand mechanical stress and thermal cycling.

The Through-Hole Assembly Process: Step-by-Step

The TH assembly process combines precision and durability. Here’s how it works:

1. PCB Design and Drilling

Hole Drilling: Holes are drilled into the PCB based on the component lead diameters.
Plated Through-Holes (PTH): Copper plating inside the holes ensures electrical connectivity between layers.

Why It Matters: Accurate hole sizing prevents lead misalignment. PCBPit uses laser drilling and CNC machines to achieve tolerances as tight as ±0.05mm.

2. Component Insertion

Manual Insertion: Used for prototypes or low-volume runs.
Automated Insertion: Axial (horizontal) and radial (vertical) inserters place components at high speeds.

Why It Matters: Automation reduces human error. PCBPit’s hybrid lines support both manual and automated insertion for flexibility.

3. Soldering

Wave Soldering: The PCB passes over a molten solder wave, which wicks into the holes to form joints.
Selective Soldering: For boards with mixed SMT/THT components, targeted nozzles solder only the through-hole parts.
Hand Soldering: Used for rework or delicate components.

Why It Matters: Proper solder profile prevents cold joints or bridging. PCBPit’s wave soldering systems feature nitrogen environments to minimize oxidation, ensuring flawless connections.

4. Inspection and Testing

Visual Inspection: Checks for solder defects or misaligned components.
Automated Optical Inspection (AOI): Validates solder joint quality.
In-Circuit Testing (ICT): Confirms electrical functionality.

Why It Matters: Rigorous testing ensures reliability. PCBPit combines AOI, X-ray, and functional testing to meet IPC Class 2/3 standards.

Advantages of Through-Hole Technology

Mechanical Strength: TH components withstand vibration, shock, and high stress—ideal for automotive or aerospace systems.
Ease of Prototyping: Simplifies manual adjustments and replacements during R&D.
Thermal Performance: Larger components dissipate heat more effectively.
High-Power Handling: Suitable for circuits requiring high voltage/current.

Challenges and Limitations

Size Constraints: TH components occupy more board space than SMDs.
Slower Production: Drilling and insertion increase assembly time.
Higher Costs: Labor and material expenses rise for complex designs.

How PCBPit Addresses These Challenges: By leveraging automated insertion, advanced soldering techniques, and design optimization support, PCBPit mitigates cost and speed inefficiencies without compromising quality.

Applications of Through-Hole Technology

THT thrives in demanding environments:

Industrial Equipment: Motor controllers, power supplies.
Aerospace and Defense: Avionics, radar systems.
Automotive: Engine control units (ECUs), LED lighting.
Medical Devices: MRI machines, patient monitors.

PCBPit serves these industries with specialized TH solutions, including conformal coating and ruggedized assemblies.

Through-Hole vs. SMT: Choosing the Right Technology

Factor	Through-Hole	SMT
Size	Larger components	Compact, high-density
Durability	High mechanical strength	Moderate
Cost	Higher for mass production	Lower for high volumes
Applications	High-power, harsh environments	Consumer electronics

Hybrid Approach: Many boards combine THT and SMT. PCBPit excels in mixed-technology assembly, offering design guidance to optimize performance and cost.

Quality Control in Through-Hole Assembly

IPC-A-610 Compliance: Defines acceptability criteria for solder joints.
Thermal Stress Testing: Ensures components withstand temperature fluctuations.
Cross-Sectional Analysis: Inspects PTH copper plating integrity.

PCBPit’s certifications (ISO 9001, ISO 13485, UL) and in-house labs guarantee adherence to global standards.

Why Choose PCBPit for Through-Hole Assembly?

Expertise: Decades of experience in high-reliability THT projects.
Advanced Equipment: Automated insertion, selective soldering, and AOI systems.
End-to-End Support: DFM analysis, component sourcing, and testing.
Scalability: Prototype to high-volume production with consistent quality.
Industry Focus: Specialization in automotive, aerospace, and medical sectors.

Whether you need a rugged industrial control board or a complex hybrid design, PCBPit delivers precision-engineered solutions.

The Future of Through-Hole Technology

While SMT dominates, THT will persist in niche markets. Innovations like advanced PTH coatings and hybrid soldering techniques will enhance its relevance. Partnering with forward-thinking manufacturers like PCBPit ensures access to cutting-edge TH capabilities.

Conclusion

Through-Hole Technology remains vital for applications where reliability trumps miniaturization. Its mechanical robustness, thermal performance, and ease of prototyping make it irreplaceable in critical industries. By collaborating with PCBPit—a manufacturer renowned for quality, expertise, and innovation—you can harness the full potential of THT while navigating its challenges effortlessly.

Ready to elevate your through-hole PCB projects? Visit PCBPit.com today to explore their services and request a quote. With PCBPit, durability meets precision—every connection counts.