Reliable Through-Hole Assembly for Complex PCBs

Through-hole technology (THT) provides superior mechanical strength and thermal cycling resistance compared to SMT. It's essential for heavy components like transformers, large capacitors, and connectors that endure physical stress. THT also offers better heat dissipation and high-voltage isolation, making it mandatory for industrial power electronics, automotive engine controls, and aerospace applications where reliability is critical.

We utilize axial and radial lead cutting/forming machines followed by automated component insertion (Axial/Radial Insertion Machines) for high-volume production. For prototypes, complex configurations, or oversized components, our certified technicians perform manual insertion followed by selective wave soldering or robotic soldering. All PTH joints are inspected under AOI (Automated Optical Inspection) and sampled for X-ray analysis on multilayer boards.

We follow IPC-A-610 Class 2 or Class 3 standards for through-hole solder joints. Key controls include: (1) Lead forming to prevent stress on component bodies; (2) Precise hole-to-lead ratios (typically 0.2-0.4mm clearance); (3) Wave solder profiling with preheating to prevent thermal shock; (4) 100% visual inspection for barrel fill (minimum 75% for Class 2, 100% for Class 3); and (5) Solderability testing per IPC-J-STD-002 to ensure proper wetting.

Absolutely. We specialize in mixed-technology assembly. The standard process flow is: (1) SMT reflow on the primary side; (2) SMT reflow on the secondary side (if double-sided); (3) THT component insertion; (4) Selective wave soldering or hand soldering for through-hole parts. For sensitive SMT components on the secondary side, we use selective soldering pallets or masking to protect existing components during the wave solder process.

We provide automated lead forming and cutting services to ensure consistent standoff heights and stress relief. Axial components are formed with specific bend radii (typically 1x lead diameter minimum) to prevent cracking. For radial components, we maintain proper spacing to avoid solder bridging. All forming tools are customized per component specification to ensure leads insert smoothly without damaging plated through-holes or causing pad lifting.

For high-current applications, we use heavy copper PCBs (2oz to 6oz) and ensure full barrel fill for maximum current carrying capacity. High-heat components receive thermal relief patterns in the copper planes to prevent soldering difficulties. We also employ press-fit connectors where soldering heat could damage sensitive terminals, and use high-temperature solder alloys (SAC305 or Sn95/Sb5) for components operating above 125°C ambient temperature.

Wave soldering is usually better for THT-dense boards and stable production runs. Selective soldering is preferred for mixed SMT and through-hole PCB assembly, especially when THT pins sit close to heat-sensitive SMT components or when only a few local joints need soldering.

Please send Gerber files, BOM, assembly drawings, polarity notes, special soldering requirements, inspection class, test procedure and any high-voltage, high-current or mechanical retention requirements. These details help us choose manual soldering, wave soldering, selective soldering or press-fit assembly correctly.