Fanway specializes in delivering efficient and reliable end-to-end PCB assembly services, precisely tailored to your unique requirements to accelerate your product success.
Fanway’s Mixed SMT and Through-Hole Technology Integration Assembly service applies both SMT and THT processes on the same printed circuit board. SMT handles high-density, high‑speed signal chips (supporting 01005 passives and 0.3mm‑pitch BGAs), while THT takes care of connectors, transformers, large capacitors, and power devices that demand mechanical strength and high current capacity. This combination is not a simple overlay and it is achieved through partitioned layout, sequential process control, and thermal coordination, allowing both technologies to work side‑by‑side without interference. While SMT accounts for over 85% of today’s PCB assembly volume, mixed assembly is the fastest‑growing segment because modern electronics almost never rely on a single technology alone.
Higher Power Density with HDI + THT Stack‑ups
On a limited board area, high‑density interconnect (HDI) routing provides compact signal networks for SMT chips, while THT components offer low‑impedance paths for power loops. The synergy boosts power‑carrying capacity per unit area by 25%, meeting higher performance demands without enlarging the board.
IPC‑A‑610 Class 2 Certification for High Reliability
All Mixed SMT and Through-Hole Technology Integration Assembly processes strictly follow IPC‑A‑610 Class 2 standards. From SMT reflow to THT wave or selective soldering, each step has defined process windows and inspection criteria. For reliability‑sensitive sectors like medical and automotive, we provide full traceability compliant with ISO 13485 and IATF 16949.
Overall Cost Optimization
Separate SMT and THT production means two workflows, two sets of logistics, and double management overhead. Mixed assembly integrates both processes on one line, reducing inter‑process handling and re‑positioning losses by over 50%, cutting total costs by 30% compared to split production.
End‑to‑End Quality Control: From SPI to X‑Ray
Mixed assembly carries higher quality risks than single‑process boards SMT joints may suffer thermal shock during wave soldering, and THT insertion may damage already‑placed SMT components. Our countermeasures include: step stencils for optimized solder paste volume, high‑temperature tape protection over SMT areas before wave soldering, and dual inspection with AOI + X‑Ray covering both visible and hidden joints (BGAs, LGAs).
Mixed PCB assembly is the process of mounting both surface‑mount (SMT) and through‑hole (THT) components on a single printed circuit board. SMT components are placed directly on the board surface and soldered via reflow; THT leads are inserted through pre‑drilled holes and soldered on the opposite side using wave or selective soldering. This “best‑of‑both” strategy harnesses SMT’s high density and miniaturization alongside THT’s superior mechanical strength and power handling. Mixed assembly is widely adopted in automotive electronics, medical devices, industrial controls, and aerospace applications.
Fanway follows a SMT‑first, THT‑second sequence for the production of Mixed SMT and Through-Hole Technology Integration Assembly and this is critical for yield. The complete flow:
PCB Cleaning & Solder Paste Printing
After board cleaning, solder paste is printed onto SMT pads via stencil. For mixed boards, a step stencil can be used to adjust paste thickness across different zones.
SMT Placement & Reflow
High‑speed pick‑and‑place machines mount SMT components, then the board goes through a reflow oven to complete SMT soldering. This step must happen before THT insertion reflow heat would damage most THT components (e.g., plastic‑housing connectors).
THT Component Insertion
Manual or automated insertion machines place THT leads into plated through‑holes. Components must sit flush against the board with straight leads, while avoiding excessive force that could crack existing SMT solder joints or warp the PCB.
Wave or Selective Soldering
For boards with many THT components, wave soldering completes all joints in one pass. For dense mixed layouts, selective soldering applies solder only to THT pads, protecting nearby SMT components from thermal exposure. Selective soldering maintains a solder wave height of 2‑5mm (vs. 8‑12mm in conventional wave soldering), significantly reducing the heat‑affected zone.
Lead Trimming, Cleaning & Inspection
Excess leads are trimmed, flux residues cleaned, followed by AOI visual inspection, X‑ray inspection (for hidden joints), and functional testing.
Mixed assembly imposes special requirements on PCB design, the following three points directly impact production yield:
Zoned Layout with ≥3mm Spacing
Clearly separate SMT and THT zones on the board. Place THT components (connectors, large capacitors) near board edges or corners, and keep fine‑pitch SMT devices (BGAs) away from the THT area that maintains at least 3mm clearance between the two zones to prevent mechanical interference during insertion and solder splash during wave soldering.
Hole Size Matching: 0.1‑0.2mm Clearance
THT pad hole diameter should be 0.1‑0.2mm larger than the component lead diameter ensuring smooth insertion. Too tight and insertion is difficult or impossible; too loose and the component shifts, leading to poor solder fill.
Thermal Relief & Keep‑out Zones
THT pads connected to large copper planes (ground, power) should use thermal relief spokes to prevent heat from being conducted away too quickly, which causes cold joints. Around selective‑soldering THT pads, reserve adequate keep‑out areas to avoid adjacent components.
Mixed assemblyMixed SMT and Through-Hole Technology Integration Assembly
Automotive Electronics
ECUs, BMS, ADAS sensor modules all these boards need dense chips for signal processing and high‑current connectors, relays, and other THT parts that withstand vibration and temperature cycling.
Industrial Controls & Power Modules
PLCs, servo drives, industrial power supplies SMT handles control logic and communications, THT mounts power MOSFETs, transformers, and large capacitors for thermal management.
Medical Devices
Patient monitors, ultrasound systems, diagnostic equipment SMT for sensor front‑ends and processor cores, THT for power connectors and frequently‑mated interfaces.
Aerospace & Defense
High‑reliability systems that demand mechanical robustness THT connections must meet MIL‑STD‑202G vibration standards.
12 Years of Mixed Assembly Experience
We have specialized in SMT‑THT mixed assembly for over a decade, building deep know‑how from DFM review to volume production. Our team understands which designs cause wave‑soldering bridges and which placements lead to insertion stress lessons that are not in textbooks but determine final yield.
ISO 9001:2015 & IPC‑A‑610 Class 2 Certified
All processes run under certified quality systems. Every board undergoes AOI, X‑Ray, and functional testing. For medical and automotive clients, we provide full traceability documentation compliant with ISO 13485 and IATF 16949.
One‑Stop Service: From Design to Delivery
We offer DFM review, component procurement, SMT+THT assembly, and final testing. Simply provide your Gerber files and BOM and we handle the rest.
Flexible Volume Capabilities
Support from prototype to high‑volume production. No NRE fees for standard mixed boards; for complex boards, we provide engineering review and process optimization advice.
Q: What is the typical lead time for mixed assembly boards?
A: Prototypes usually take 5‑7 working days, small volumes (<1000 pcs) 7‑10 days, and large volumes are evaluated case‑by‑case, generally 10‑15 working days.
Q: Which THT components require selective soldering instead of wave soldering?
A: When SMT components (especially fine‑pitch BGAs, QFNs) are positioned close to THT pads, or when THT components are heat‑sensitive (e.g., connectors with plastic housings), selective soldering is recommended. It heats only the THT joint area, protecting the rest of the board from thermal exposure.
Q: Does Mixed SMT and Through-Hole Technology Integration Assembly require special PCB substrate materials?
A: Standard FR‑4 is sufficient for most mixed assemblies. However, if the board carries high‑power THT components (transformers, power MOSFETs), we recommend high‑Tg material (Tg ≥ 150°C) to withstand wave‑soldering thermal shock.
Q: Can SMT and THT components be placed on the same side?
A: Yes. Placing both on the top side is the simplest approach, leaving the bottom clear for wave soldering. However, ensure at least 2‑3mm clearance between SMT pads and THT holes.
Q: Does Fanway support lead‑free soldering?
A: Yes. Our reflow and wave soldering systems are fully compatible with lead‑free alloys (SAC305, etc.), with temperature profiles set accordingly.
Q: What defect rate can we expect for mixed assembly?
A: With thorough DFM involvement, our mixed assembly first‑pass yield typically exceeds 97%. Key control points: layout review during design, SMT protection before wave soldering, and dual AOI+X‑Ray inspection.
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Building 3, The First Industrial Zone of Mingjinhai, Shiyan Street, Bao'an District, Shenzhen, Guangdong, China, Zip Code:518108
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