Through-Hole PCB Assembly
Reliable through-hole assembly for components that demand mechanical strength and high-current carrying capacity. We deliver IPC-A-610 Class 3 compliant solder joints with 75% minimum hole fill, selective soldering accuracy within ±3°C, and 100% electrical testing on every board.
Why Through-Hole Assembly Still Matters
Surface-mount technology dominates modern PCB assembly, but through-hole technology (THT) remains indispensable for specific applications. The reason is straightforward: a through-hole solder joint extends through the board and fills the plated via, creating a mechanical bond that is 3-5x stronger than an SMT pad attachment. When a connector is going to be plugged and unplugged hundreds of times, or a transformer weighs 50 grams and sits on a board subject to vibration, that mechanical strength is not optional — it is the difference between a product that lasts and one that fails in the field.
Through-hole also excels in high-current applications. A standard THT pin in a 1.0mm plated through-hole can carry 3-5 amps reliably, while an equivalent SMT pad is limited by the copper trace width and thermal relief pattern. Power supplies, motor drives, and industrial controllers still rely on THT for their power stages for this reason. The IPC standards specifically address THT joint requirements in IPC-A-610, with distinct acceptance criteria for vertical hole fill, wetting, and fillet shape that have no SMT equivalent.
The trade-off is cost and density. THT components require more board space, and the assembly process is slower — often requiring manual insertion and hand soldering. Our job is to minimize that cost penalty through process optimization: automated insertion where volume justifies it, selective soldering instead of hand soldering for mixed boards, and DFM feedback that catches THT-specific issues before they become production problems.
Through-Hole Assembly Capabilities
Wave Soldering
High-throughput wave soldering for predominantly THT boards. Our dual-wave system handles lead-free SAC305 at 260°C and Sn63/Pb37 at 248°C with nitrogen...
Selective Soldering
Precision selective soldering for mixed-technology boards where wave soldering would damage adjacent SMT components. Our drop-jet and mini-wave systems...
Hand Soldering & Rework
IPC J-STD-001 certified operators for low-volume, high-mix assemblies and rework. Temperature-controlled stations with JBC and Metcal irons maintain tip...
Automated Insertion
Axial and radial component insertion machines for high-volume THT production. Axial sequencers handle components from 3mm to 26mm body length with 0.2mm lead...
100% Inspection & Testing
Every THT board undergoes visual inspection per IPC-A-610, with AOI for solder joint quality and ICT or flying-probe for electrical validation. We perform...
Lead-Free & Leaded Capability
Full RoHS-compliant SAC305 lead-free processing alongside Sn63/Pb37 leaded solder for military, aerospace, and exempt applications. We maintain separate...
Through-Hole Assembly: Our Specs vs. Industry Standard
Most PCB assembly shops treat through-hole as an afterthought — something they do because they have to, not because they specialize in it. The table below shows where we invest in THT-specific capability rather than treating it as a secondary process.
| Parameter | IPC Standard | Our Capability | Industry Benchmark |
|---|---|---|---|
| Hole Fill (Vertical) | 75% min (Class 3) | ≥ 90% typical | 75-80% |
| Solder Joint Temperature Accuracy | Per J-STD-001 profile | ±3°C (selective soldering) | ±5-8°C |
| Lead-Free Solder Alloy | SAC305 per J-STD-006 | SAC305, SAC405, Sn100C | SAC305 only |
| Wave Solder Board Width | N/A | Up to 400mm | 300-350mm |
| Selective Solder Nozzle Count | N/A | Dual nozzle + drop-jet flux | Single nozzle |
| Inspection Level | Sample per IPC-A-610 | 100% visual + AOI | Sample or AOI only |
| Connector Pull Test | Per IEC 60352-5 | 100% on critical joints (≥5N) | Sample-based |
| Certifications | ISO 9001 | ISO 9001 + IATF 16949 + J-STD-001 | ISO 9001 |
References: IPC-A-610G Acceptability of Electronic Assemblies, J-STD-001G Requirements for Soldered Electrical and Electronic Assemblies, IEC 60352-5 Solderless connections. See JEDEC for component-level thermal and moisture sensitivity standards that affect THT processing.
When to Choose Through-Hole vs. Surface Mount
This is the decision framework we walk through with customers during DFM review. If your design falls into any of the categories below, through-hole is the right call — not because it is cheaper, but because it is more reliable for that specific use case.
Choose Through-Hole When:
- Components face repeated mechanical stress (connectors, switches, relays with >100 mating cycles expected)
- Individual pins carry >5A continuous current (power supplies, motor drivers, battery management)
- Components weigh >15g per unit and board is subject to vibration or shock (transformers, large inductors, electrolytic capacitors >18mm diameter)
- Operating environment exceeds 105°C ambient (THT joints tolerate thermal cycling better than SMT due to lead compliance)
- Military or aerospace application requiring mil-spec components only available in THT packages (per IPC standards)
Stick with SMT When:
- Board space is the primary constraint and component density must exceed 15 components per cm²
- All components are available in SMT packages and no pin carries more than 3A
- Production volume exceeds 10,000 units and per-board cost must be minimized (SMT placement is 5-10x faster)
- High-frequency signals above 1GHz where lead inductance from through-hole pins degrades signal integrity
- Double-sided component placement is required (THT pins protruding through the board limit bottom-side routing)
Through-Hole Assembly Process
1
DFM Review & Process Planning
Our engineers review your Gerber files, BOM, and assembly drawings to identify THT-specific challenges: component clearance, thermal sensitivity of adjacent...
2
SMT Processing (If Mixed-Technology)
For mixed boards, SMT components are placed and reflowed first. We apply solder mask or peelable solder resist to protect SMT joints during subsequent wave...
3
THT Component Insertion
Components are inserted manually, semi-automatically, or via automated insertion machines depending on volume and component type. Axial and radial components...
4
Soldering (Wave / Selective / Hand)
The board enters the soldering process determined in step 1. Wave soldering uses a dual-wave system (turbulent + smooth) with nitrogen inerting. Selective...
5
Cleaning & Inspection
Post-soldering, boards are cleaned using no-clean or aqueous processes depending on flux type and customer requirements. Visual inspection per IPC-A-610...
6
Electrical Testing & Shipment
Final electrical testing (ICT, flying probe, or functional test) validates circuit integrity. We test 100% of THT solder joints for continuity and insulation...
Soldering Technology Details
Case Study: Industrial Motor Controller — Mixed SMT/THT Assembly
Challenge
An industrial automation OEM needed 8,000 motor controller boards with 47 THT components (power MOSFETs in TO-247, 15A terminal blocks, and a 200g transformer) alongside 380 SMT components. Previous supplier had a 3.2% defect rate on THT joints due to inconsistent hole fill and solder bridging between adjacent SMT components during wave soldering.
Solution
We redesigned the soldering approach: SMT components were reflowed first with a 4mm keep-out zone around THT footprints. Selective soldering replaced wave soldering for the THT stage, using a dual-nozzle system with nitrogen inerting and programmable dwell times (2.5s for TO-247 pins, 1.8s for terminal blocks). Peelable solder mask protected adjacent SMT joints. SAC305 alloy with Sn100C for the transformer pins to reduce copper dissolution.
Results
THT joint defect rate dropped from 3.2% to 0.15% — a 95% improvement. Hole fill averaged 92% vertical fill across all THT joints. Per-board assembly cost decreased 28% by eliminating manual touch-up and rework. Lead time reduced from 6 weeks to 3.5 weeks. Zero field failures reported after 12 months in operation across 8,000 units deployed in factory environments.
Frequently Asked Questions
What is the minimum order quantity for through-hole PCB assembly?
Our MOQ for through-hole PCB assembly starts at 25 pieces for prototypes and 100 pieces for production runs. For mixed-technology boards (SMT + THT), we can process as few as 10 boards in our NPI line. Lead time for prototype THT assembly is typically 5-7 business days.
How long does through-hole PCB assembly take compared to SMT?
Through-hole assembly is inherently slower than SMT due to the manual or semi-automated insertion process. A typical THT-only board takes 3-5 days longer than an equivalent SMT board. However, for mixed-technology boards, we run SMT and THT in parallel where possible, adding only 1-2 days to the overall lead time. Selective soldering can reduce THT cycle time by up to 60% compared to hand soldering.
What file formats do you need for a through-hole assembly quote?
We require Gerber files (RS-274X) for the PCB fabrication, a Centroid/Pick-and-Place file (CSV or TXT format), a complete BOM with manufacturer part numbers, and assembly drawings showing component orientation for polarized parts. For through-hole specific requirements, please also specify any torque requirements for connectors and preferred solder alloy (SAC305, Sn63/Pb37, or other).
When should I choose through-hole over surface mount for my design?
Choose through-hole when your design involves components subject to mechanical stress (connectors, transformers, large capacitors, power semiconductors in TO-220/TO-247 packages), high-current paths (>5A per pin), or when you need reliable board-edge connections. THT joints have 3-5x the mechanical strength of SMT joints per IPC-A-610 Class 3 criteria. For everything else, SMT is more cost-effective and space-efficient.
What soldering methods do you use for through-hole assembly?
We employ three methods depending on component mix and volume: wave soldering for high-volume, predominantly THT boards (solder pot temperature 260°C for SAC305); selective soldering for mixed-technology boards where SMT components are already reflowed; and hand soldering for low-volume, high-mix, or components too large for automated processes. All methods comply with IPC-A-610 and J-STD-001 standards.
Can you assemble mixed SMT and through-hole boards?
Yes, mixed-technology assembly is our most common request. The standard process flow is: solder paste print → SMT placement → reflow soldering → THT insertion → selective soldering or hand soldering → inspection. We handle boards with up to 500+ THT components alongside 2000+ SMT components. The key design consideration is maintaining a 3mm minimum keep-out distance between SMT components and THT solder joints to prevent solder bridging during wave or selective soldering.
What certifications apply to your through-hole assembly process?
Our through-hole assembly operates under ISO 9001:2015 quality management, IPC-A-610 (Class 1, 2, and 3) workmanship standards, J-STD-001 soldering requirements, and IPC-7711/7721 for rework and repair. For automotive projects, we comply with IATF 16949. All solder operators are certified to IPC J-STD-001 with annual recertification, and our soldering processes are profiled per IPC-7530 guidelines.
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Learn MoreReady to Start Your Through-Hole Assembly Project?
Send us your Gerber files, BOM, and assembly drawings. Our engineering team will review your design for THT-specific DFM issues and return a detailed quote with process recommendations within 24 hours.
Reviewed by: Engineering Team, pcbinsider | Last updated: 2026-04-15