Through Hole vs. SMT: When Traditional PCB Assembly Outshines Modern Technology

Understanding Through Hole PCB Assembly (THT)

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Through Hole Technology (THT) remains a cornerstone in electronics manufacturing, valued for its mechanical robustness and reliability. In an industry where the global PCB market is projected to reach $125 billion by 2028, THT retains its relevance in specialized applications.

Defining Through Hole Technology

THT involves inserting component leads through drilled holes in a PCB, with soldering on the opposite side to form a secure mechanical bond. This method excels in high-stress environments, supporting components like power resistors, transformers, and heavy connectors.

The THT Assembly Process

1. Component Preparation: Leads are trimmed and tinned for optimal soldering.
2. Mechanical Insertion: Components are placed into pre-drilled holes manually or via automated inserters.
3. Wave Soldering: A molten solder wave creates permanent joints.
4. Post-Processing: Cleaning and visual inspection for defects.

Key Traits of THT Components

• High Power Handling: Supports currents >10A and voltages >500V.
• Vibration Resistance: Ideal for aerospace (e.g., satellite systems) and heavy machinery.
• Repairability: Easier component replacement during prototyping.
• Thermal Stability: Withstands temperature swings from -55°C to +125°C.

Decoding Surface Mount Technology (SMT)

SMT Fundamentals

SMT attaches components directly to the PCB surface using solder paste and reflow heating. This method enables miniaturization, with components as small as 01005 (0.4mm x 0.2mm), driving the consumer electronics revolution.

Term	Definition
SMT Process	Solder paste application → component placement → reflow soldering
Key Advantage	90% smaller board footprint compared to THT
Production Speed	Up to 50,000 components/hour via automated pick-and-place machines

The SMT Assembly Workflow

1. Stencil Printing: Solder paste is deposited on PCB pads.
2. High-Precision Placement: Robotic arms position components with ±25μm accuracy.
3. Reflow Soldering: Temperature-controlled ovens melt the paste.
4. Advanced Inspection: AOI and X-ray systems check for voids and misalignments.

SMT Component Characteristics

• Miniaturization: Enables double-sided PCB layouts.
• High-Speed Compatibility: Reduces signal delay in RF and digital circuits.
• Cost Efficiency: 30% lower labor costs for high-volume runs.
• Design Flexibility: Supports complex packages like BGA and QFN.

THT vs. SMT: Key Contrasts

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Component Size & Design Freedom

THT’s larger components limit miniaturization, while SMT’s tiny footprints enable dense, compact designs.

Aspect	THT	SMT
Component Size	≥1206 (3.2mm x 1.6mm)	Down to 01005 (0.4mm x 0.2mm)
Board Density	Single-sided preferred	Supports 4+ layers with blind vias
Design Flexibility	Limited by leaded components	High flexibility for complex layouts

Assembly Process & Automation

THT’s manual insertion steps contrast with SMT’s fully automated workflow:

• THT: Wave soldering with 50% manual intervention
• SMT: 95% automated, from paste printing to inspection

Reliability & Mechanical Strength

THT outperforms in harsh environments:

• Military avionics: THT joints survive 50G shock loads
• Industrial controls: Withstands 20-2000Hz vibration
• SMT: Prone to solder fatigue under continuous stress

Cost & Production Scalability

Metric	THT	SMT
Labor Cost	2x higher than SMT	Low due to automation
Setup Cost	500-1000 per design	2000-5000 for stencils
Economy of Scale	Optimal for <1000 units	Cost-effective at >5000 units

When THT Outperforms SMT

High-Reliability Applications in Extreme Environments

THT dominates in sectors where failure is not an option:

• Aerospace: NASA’s Mars rover uses THT for power distribution boards, enduring -150°C to +125°C cycles.
• Military: DoD-certified THT components withstand radiation and ballistic shock.
• Oil & Gas: Subsea equipment relies on THT for corrosion resistance.

Industry	THT Use Case	Survival Conditions
Aerospace	Satellite power supplies	10+ years in vacuum
Defense	Radar systems	50G mechanical shock
Industrial	Wind turbine controls	-40°C to +85°C

Mechanical Stress & Durability Demands

Components like transformers and heavy connectors require THT’s robust mounting:

• Vibration Resistance: THT joints reduce failure rates by 70% in automotive engines.
• High Power Handling: THT supports 100W+ components without thermal runaway.

Prototyping & Low-Volume Production

THT’s ease of modification makes it ideal for R&D:

• Quick Iterations: Components can be replaced without de-soldering entire boards.
• Cost-Efficiency: Reduces prototyping costs by 40% versus SMT.

Mixed-Technology Designs

Combining THT and SMT optimizes performance:

• THT for high-power components (inductors, relays)
• SMT for signal processing (ICs, passive components)
• Example: Medical imaging equipment uses mixed designs for durability and precision.

Industry Applications of THT and SMT

THT-Driven Industries

• Power Electronics: Inverters, motor controls, and battery management systems.
• Heavy Machinery: Industrial robots, CNC machines, and manufacturing equipment.
• Medical Devices: Life support systems requiring fail-safe operation.

SMT-Dominated Sectors

• Consumer Electronics: Smartphones, wearables, and IoT devices (85% of PCBAs use SMT).
• Telecom: 5G base stations and network equipment.
• Automotive: Advanced driver-assistance systems (ADAS) and infotainment.

Product Examples

• THT: Industrial power supplies, military radios, aircraft avionics
• SMT: Smartwatches, laptop motherboards, wireless routers
• Mixed: Electric vehicle controllers, medical MRI machines

Choosing the Right Assembly Method with LTPCBA

Key Decision Factors

1. Environmental Stress: THT for vibration/heat; SMT for controlled environments.
2. Power Requirements: THT for >5A circuits; SMT for low-power designs.
3. Production Volume: THT for <1000 units; SMT for mass production.
4. Component Size: SMT for 0402 or smaller; THT for through-hole parts.

Design & Compliance Considerations

LTPCBA ensures:

• IPC-A-610 Class 3 compliance for critical applications
• RoHS/REACH certification for environmental safety
• DFM (Design for Manufacturing) reviews to optimize assembly

Testing & Validation

Rigorous testing protocols:

• THT: Vibration testing (5-2000Hz, 2g acceleration)
• SMT: Thermal cycling (-40°C to +125°C, 1000 cycles)
• Mixed Designs: Combined stress testing for both technologies

FAQ

What’s the core difference between THT and SMT?

THT uses leaded components inserted through holes, while SMT mounts components directly on the PCB surface.

Why choose THT for automotive applications?

THT resists engine heat (up to 150°C) and vibration, critical for under-hood electronics.

Can a PCB use both THT and SMT?

Yes—mixed technology PCBs combine THT for heavy components and SMT for miniaturization, common in industrial and medical devices.