Through-Hole Technology vs. SMT: When to Choose Through-Hole for Electronics Manufacturing

In electronics manufacturing, selecting between Through-Hole Technology (THT) and Surface Mount Technology (SMT) depends on your project’s unique demands. While SMT dominates for compact, high-volume devices, through-hole technology remains irreplaceable for applications requiring exceptional durability, ease of repair, and reliability in harsh environments. This guide compares the two technologies and outlines scenarios where through-hole is the superior choice.

Key Insights

• Durability first: Through-hole components withstand vibration, thermal stress, and mechanical shock far better than SMT, with failure rates 8x lower in stress tests.
• Repair and flexibility: THT’s hand-solderable leads simplify repairs and prototyping, reducing maintenance costs by 50% compared to SMT.
• Specialized applications: High-power devices, industrial machinery, and aerospace systems rely on through-hole for its ability to handle high currents and extreme conditions.

Through-Hole vs. SMT: Core Differences

Mounting and Mechanical Strength

Through-hole technology involves inserting component leads through drilled holes in the PCB, with solder joints formed on the opposite side. This creates a mechanical anchor that distributes stress across the board, making it far more resistant to physical forces:

• THT advantages:
  • Leads penetrating the PCB create a "mechanical lock," withstanding vibration (10–2000Hz) and thermal cycling (-40°C to 125°C) 3x better than SMT.
  • Solder joints in THT assemblies survive over 1,000 thermal cycles before weakening, compared to 300–500 cycles for SMT.
• SMT characteristics:
  • Components attach to pads on the PCB surface, offering no mechanical anchoring—prone to detachment in high-stress environments.
  • Ideal for lightweight, compact designs (e.g., smartphones) where space is critical.

Assembly and Cost

The manufacturing processes for THT and SMT differ significantly, impacting speed and cost:

Factor	Through-Hole Technology	Surface Mount Technology
Assembly Method	Manual or semi-automated insertion; hand soldering.	Fully automated pick-and-place machines; reflow soldering.
Speed	Slower (20–50 components/hour per operator).	Faster (1,000+ components/hour per machine).
Labor Cost	Higher (50–70% of total assembly cost).	Lower (10–20% of total assembly cost).
Setup Cost	Low (no expensive stencils or machines).	High (stencils, pick-and-place equipment).
Volume Suitability	Best for small batches (<1,000 units).	Ideal for high volume (>10,000 units).

Design Impact

THT and SMT impose distinct constraints on PCB design:

• THT considerations:
  • Requires drilled holes (minimum size = lead diameter + 0.25mm) and larger pads (diameter = hole size + 0.7mm), increasing PCB size.
  • Limits component density (typically 10–20 components per square inch).
• SMT advantages:
  • Enables smaller PCBs with higher density (up to 100 components per square inch).
  • Supports dual-sided mounting, reducing board size by 30–50% compared to THT.

Advantages of Through-Hole Technology

Superior Mechanical Reliability

THT’s lead-through design makes it indispensable for harsh environments:

• Vibration resistance: In automotive tests (10–2000Hz), <2% of THT components fail, compared to 10%+ for SMT.
• Thermal stability: Through-hole solder joints dissipate heat better, making them suitable for power devices (e.g., transformers, MOSFETs) handling >10A.
• Longevity: THT assemblies in industrial equipment often operate for 15+ years, outlasting SMT counterparts by 5–7 years.

Ease of Repair and Prototyping

THT simplifies troubleshooting and design iterations:

• Manual rework: Components can be removed and replaced with basic tools (soldering iron, desoldering braid), reducing repair costs to <20 per component (vs. 50–$100 for SMT).
• Prototyping flexibility: Breadboards and socketed THT components allow quick design changes without specialized equipment.
• Testing accessibility: Exposed leads make it easier to probe circuits during debugging.

High-Power Handling

Through-hole components excel in applications requiring high current or voltage:

• Current capacity: THT leads (0.5–2mm diameter) carry 5–10x more current than SMT pads (0.2–0.5mm²), making them ideal for power supplies and motor controllers.
• Heat dissipation: Larger lead sizes and solder joints dissipate heat more efficiently, preventing overheating in devices like inverters and amplifiers.

Limitations of Through-Hole Technology

Size and Density

THT’s larger footprint and hole requirements restrict miniaturization:

• PCB size: A THT board with 50 components is typically 2–3x larger than an SMT equivalent.
• Component size: THT parts (e.g., 0.25W resistors) are 5–10x larger than SMT alternatives (0402 resistors).

Cost at Scale

For high-volume production, THT becomes cost-prohibitive:

• Labor inefficiency: Manual assembly costs rise exponentially with volume (e.g., 10/unit for 100 units vs. 50/unit for 10,000 units).
• Material waste: Drilling holes generates 30% more PCB scrap compared to SMT.

When to Choose Through-Hole Technology

High-Stress Environments

THT is mandatory for applications with extreme conditions:

• Aerospace and defense: Avionics and military equipment require THT’s vibration resistance (e.g., radar systems, missile guidance).
• Automotive: Engine control modules and powertrain electronics use THT to withstand temperature swings (-40°C to 125°C) and engine vibration.
• Industrial machinery: Factory robots, CNC controllers, and power distribution units rely on THT for durability in dusty, high-shock environments.

High-Power Applications

THT dominates in power-dense systems:

• Power supplies: Transformers, rectifiers, and capacitors in 100W+ supplies use THT for current handling.
• Heavy machinery: Crushers, pumps, and generators require THT components to manage high voltages (1000V+) and currents (50A+).

Prototyping and Low-Volume Production

For small batches or design iterations, THT offers cost and flexibility benefits:

• Startups and R&D: THT’s low setup costs (500–1,000) make it ideal for testing new ideas without investing in SMT tooling.
• Custom equipment: Specialized devices (e.g., lab instruments, medical prototypes) with <100 units benefit from THT’s easy rework.

Frequent Maintenance Requirements

Products needing regular repairs favor THT:

• Field service: Telecom towers, utility meters, and marine electronics use THT for on-site repairs with minimal tools.
• Legacy systems: Older equipment (e.g., industrial PLCs) relies on THT components that are easy to source and replace.

Decision Checklist: THT vs. SMT

Use this framework to choose the right technology:

Factor	Choose Through-Hole If...	Choose SMT If...
Environment	Operating in harsh conditions (vibration, extreme temps).	Used in controlled environments (e.g., offices).
Volume	Producing <1,000 units.	Producing >10,000 units.
Size	PCB size is not critical.	Miniaturization is a priority.
Power	Handling >10A or 100V.	Low-power (≤5A, ≤50V) and high-frequency.
Repair Needs	Frequent maintenance or field service is required.	Repairs are rare or handled in factories.

FAQ

Q: Can THT and SMT be used together?

A: Yes. Mixed-technology PCBs combine THT for power/mechanical components (e.g., connectors) and SMT for dense, low-power parts (e.g., ICs), balancing performance and size.

Q: Why are some components only available in THT?

A: Large, high-power parts (e.g., 100W resistors, heavy-duty connectors) require THT’s mechanical strength to handle their weight and current.

Q: Is THT becoming obsolete?

A: No. THT remains critical in aerospace, automotive, and industrial sectors, with its market projected to grow from 38 billion (2023) to 69.76 billion (2032) due to demand for reliable, durable electronics.

Through-hole technology is not a relic of the past but a specialized solution for applications where reliability, power handling, and repairability matter most. By understanding its strengths and limitations, manufacturers can make informed choices that align with their project’s needs—whether that means THT, SMT, or a hybrid approach.