Why Through-Hole Technology Remains Relevant in the SMT-Dominated Era

Despite the overwhelming shift toward surface-mount technology (SMT) in consumer, telecom and mobile products, through-hole (THT) PCB assembly continues to hold a strong position in 2026 for applications where mechanical strength, long-term reliability under thermal cycling, vibration resistance, ease of manual rework, or high-current handling are non-negotiable requirements.

At STHL, with 18 years of combined SMT and THT manufacturing experience, we operate dedicated selective soldering lines, wave soldering machines, and hand-assembly stations alongside our high-mix SMT capacity. We regularly produce mixed-technology boards for customers in automotive, industrial controls, avionics, medical equipment, rail signaling, military/aerospace, and energy infrastructure segments across the United States, Europe, China, and Southeast Asia. This article explains why THT assembly is far from obsolete in 2026, when it is the right choice, key process considerations, common challenges, and how STHL helps customers achieve first-pass success.

Primary Application Areas for THT in 2026

High-Power and High-Voltage Circuits

THT components (especially large connectors, terminal blocks, high-power resistors, electrolytic capacitors, and transformers) excel in applications carrying >10 A continuous current or working voltages >400 V.

Products Exposed to Severe Mechanical Stress

Heavy vibration, shock, and repeated thermal cycling favor THT’s superior solder-joint mechanical strength.

Designs Requiring Easy Field Serviceability

THT parts are easier to desolder and replace with standard tools — a critical advantage in industrial, medical, rail, and defense equipment.

Legacy Product Support & Long-Life Programs

Many aerospace, defense, rail signaling, and industrial automation platforms have 15–30 year lifecycles and still specify through-hole parts that were qualified decades ago.

Safety-Critical and High-Reliability Segments

Certain standards (e.g., railway EN 50155, medical IEC 60601-1) still prefer or require THT for specific functions.

When Should You Choose THT over SMT in 2026?

Current Carrying Capacity > 10–15 A Continuous

SMT can handle high current with wide copper traces or thick copper (4–8 oz), but large THT connectors and terminal blocks remain the industry standard for field wiring.

Repeated Thermal Shock or Extreme Vibration

THT solder joints provide significantly higher shear and peel strength than SMT fillet joints.

Large or Heavy Components

Transformers >10 g, large electrolytic capacitors (>1000 μF), high-power resistors, relays, and DIN-rail terminal blocks are almost always THT.

Regulatory or Qualification Legacy Requirements

Many MIL, DO-160, EN 50155, and IEC 61508 qualified designs still mandate through-hole for certain functions.

Low- to Medium-Volume Production with Frequent Engineering Changes

THT allows easier manual rework and component swaps during prototype and early production phases.

STHL’s engineering team provides free DFM consultation to help you decide the optimal mix of SMT and THT for your specific reliability, cost, and lifecycle requirements.

Uncertain whether THT is right for your next project? Let STHL’s engineers review your design and give you a clear recommendation. Request Free DFM & Technology Review →

Modern THT Assembly Process at STHL (2026)

While many legacy factories still rely on outdated wave solder pots, leading manufacturers like STHL use selective soldering and robotic soldering cells that offer far better control and repeatability.

Typical Process Flow

• SMT-first assembly (if mixed board) → full SMT reflow
• Selective soldering of THT components using mini-wave or laser-assisted nozzles
• Manual through-hole insertion & hand soldering for low-volume or very large/heavy parts
• Post-wave / selective AOI and visual inspection
• In-circuit test (ICT) and functional test (FCT)
• Conformal coating or potting when required
• Final mechanical assembly & packaging

Selective Soldering Advantages

• Precise flux and solder application → reduced flux residue
• Minimal thermal stress on nearby SMT components
• Nitrogen blanket option → brighter, more reliable joints
• Programmable parameters for each joint → repeatable quality

STHL operates multiple ERSA Powerflow and SEHO selective soldering systems with nitrogen atmosphere and dual-pot capability for leaded and lead-free alloys.

Most Common THT Assembly Defects & Prevention

STHL’s first-pass yield on mixed-technology boards consistently exceeds 99.5% thanks to real-time process monitoring and closed-loop selective soldering.

Why Choose STHL for Your THT & Mixed-Technology PCBAs?

• 18 years combined SMT + THT experience
• Dedicated selective soldering cells (ERSA, SEHO) with nitrogen and dual alloy capability
• Full in-house ICT, FCT, AOI, X-ray, and environmental stress screening
• Global component sourcing with long-term safety stock programs
• Fast prototyping (5–10 days) and medium-to-high volume production
• Full compliance with IPC-A-610 Class 3, ISO 9001, IATF 16949, and RoHS/REACH

Whether your product requires selective THT on a high-density SMT board, full through-hole legacy design, or hybrid assembly for rail/medical/industrial use, STHL delivers consistent quality and on-time delivery.

Need reliable THT or mixed-technology assembly in 2026? STHL’s team is ready to support your next project.

Get Your Project Started with Confidence

 Contact STHL today for a free DFM review, process recommendation, and competitive quotation.

18 Years • Global Reach • High-Reliability Focus