PCB Assembly Manufacturing Process - JLCPCB Factory Tour

Printed circuit board assembly (PCB assembly manufacturing) is where a circuit design becomes a functional electronic product. Even with a perfectly fabricated PCB, poor assembly processes can lead to defects, reliability issues, and costly rework.

In this factory tour, we walk through the complete PCB assembly manufacturing process at JLCPCB—from solder paste printing and automated component placement to reflow soldering, inspection, and final quality control. You'll see how a modern PCB assembly line operates, what equipment is used at each stage, and how consistency and yield are maintained at scale.

Whether you're an engineer validating a design, a startup preparing for production, or a buyer evaluating a PCB assembly factory, this guide provides a clear, step-by-step view of how professional circuit board assembly is done.

PCB Assembly at JLCPCB

JLCPCB provides a fully integrated PCB assembly manufacturing service, covering component sourcing, SMT and through-hole assembly, reflow soldering, inspection, and final quality control. By combining automated production lines with standardized process control, JLCPCB ensures consistent assembly quality from prototype to volume production.

1- Parts Preparation

Once customers upload their design files, including Gerber files and the Bill of Materials (BOM), JLCPCB engineers generate manufacturing data and prepare all required components for assembly. Components are sourced from JLCPCB's in-house parts library, which includes 610,000+ SMT and through-hole components.

BOM data is automatically parsed by the assembly system to match part numbers, package types, and quantities, ensuring accurate feeder loading for pick-and-place machines.

2- Solder Paste Printing

Solder paste printing is performed using stainless steel stencils to deposit a precise and repeatable volume of solder paste onto each PCB pad. Stencil preparation runs in parallel with PCB fabrication and component preparation to minimize lead time.

Once PCB fabrication is complete, boards are transferred directly to the solder paste printing line to ensure process continuity and paste consistency.

3- Solder Paste Inspection (SPI)

After printing, solder paste deposits are inspected using automated Solder Paste Inspection (SPI) systems. SPI measures paste height, area, and volume to verify that each pad has received the correct solder amount.

This early inspection step helps prevent defects such as insufficient solder, bridging, or open joints before components are placed.

4- Component Placement (Pick-and-Place)

Automated pick-and-place machines accurately position SMT components onto the printed solder paste. Components are supplied via reels, tubes, or trays and placed according to X-Y coordinates defined in the placement file.

Vision systems verify component orientation and placement accuracy, enabling high-speed assembly while maintaining tight positional tolerances.

5- Reflow Soldering

Reflow soldering permanently attaches SMT components to the PCB using a controlled thermal profile. Boards pass through a multi-zone reflow oven, where solder paste is gradually preheated, reflowed, and cooled.

Proper thermal profiling ensures reliable solder joints while preventing component damage or thermal stress.

6- Assembly Inspection and Quality Control

After reflow, assembled PCBs undergo Automated Optical Inspection (AOI) to detect defects such as misalignment, insufficient solder, or solder bridges.

For components with hidden solder joints, such as BGAs, X-ray inspection is used to verify joint integrity. Boards that pass inspection proceed to cleaning, testing (if required), and final packaging.

7- Final Delivery and Manufacturing Assurance

By combining automated equipment, standardized inspection, and integrated component sourcing, JLCPCB delivers reliable PCB assembly manufacturing at scale.

After assembly, each board undergoes final inspection and functional verification. Approved boards are then thoroughly cleaned to remove flux residues and contaminants before secure packaging and delivery.

Every step of the process is designed to maximize yield, consistency, and cost efficiency—making professional PCB assembly accessible to engineers, startups, and production teams worldwide.

Conclusion

Making electronics manufacturing simpler and more affordable is at the core of JLCPCB's mission.

With intelligent production management, advanced automated equipment, and large-scale manufacturing capabilities, JLCPCB delivers high-quality PCB assembly at highly competitive prices.

To help engineers and makers bring ideas to life without budget constraints, JLCPCB is currently offering $70 in new user coupons.

Sign up on the JLCPCB official website today and start your PCB manufacturing and assembly project with confidence.