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Everything you need to know about SMT Lines

SMT technology is becoming pretty popular in the tech industry, and for some good reasons. In the past, the process of manufacturing electronic devices was long and complicated. Manufacturers had to use wires to attach components onto PCB via holes. In case of an error, the repairing procedure was even worse. However, in the modern era, we now have SMT which is a technology that manufacturers utilize to mount components onto PCBs. Mounting various components on PCBs directly eliminates the need for wires which makes gadgets bulky. Hence, thanks to SMT technology, we have compact, efficient devices such as smartphones in the 21st century. Comparing SMT to traditional electronic assembly processes, you will find that SMT has:

  • High density
  • High reliability
  • Low cost
  • Miniaturization
  • Sound field automation

 So yes, the SMT technology is fascinating, but what does the SMT line or SMT production line entail? And which equipment help process PCBs using SMT technology?

What exactly is SMT Line

We can group SMT lines into two classes according to the level of automation; we hence have:

  • Automatic production lines
  • Semi-automatic production lines

We can also group SMT lines according to their size, where we will have:

  • Large production lines
  • Medium production lines
  • Small production lines

Automatic Production Lines

The automatic SMT production line uses production line equipment that are all fully automated. The entire process hence does not require manual handling.

Semi-automatic production Line

The press, in this case, is semi-automatic. That means that the entire process is not fully automatic. You hence might find:

  • Manual printing of PCBs or
  • The Manual loading of PCBs or
  • Manual unloading of PCBs

One major factor to consider in the PCB production process is your client’s understanding of the entire SMT production process. Your client cannot rate your work without actually understanding what you are doing. Hence here is a basic breakdown of the SMT production line.

SMT Line Process

DFM/DFA check

Once the production team receives a PCB order, they must validate the PCB design. To do so, they must pass the order through a DFM/DFA check. The DFM/DFA check verifies consistency across various design documents, for example:

  • Centroid
  • Gerbers
  • BoM

It also checks on:

  • Part spacing
  • Footprint accuracy
  • Clear orientation marking

The DFM/DFA process tries as much as possible to minimize the probability of there being a design error.

PCB Fabrication

When the DFM/DFA process is complete, the PCB order now moves on to the fabrication stage. In this stage, the operators build a bare PCB board using the following steps:

  • Material lamination
  • Material drilling
  • Copper etching/deposition

These processes have to follow set specifications.

The stencil, which is pretty crucial for screening solder paste, is also generated in this stage. Finally, the production team has to add surface finish and solder mask onto the board before printing silkscreen over the PCB.

Inspection of Material  

The procurement team works hand in hand with the fabrication team to ensure that materials are ready for utilization. Therefore, immediately the bare print circuit board is ready for assembly, there is no delay due to lack of materials. In doing so, the assembly company can speed up production.

However, as these parts come into the PCB assembly facility, they have to go through an incoming quality control team. The IQC team inspects every component thoroughly before warehousing any component or material.

Inspection includes:

  • Sample operation testing
  • Date code verification
  • Entry into software material/component management system

The sophisticated software system in use at this stage utilizes FIFO (first in, first out) rules to check each item. It hence ensures every part in use during the PCB assembly process works in perfect condition.

SMT PCB Loading (done by the PCB Loader)

Here the loading of print circuit boards onto an SMT stencil printer takes place automatically. Operators place the print circuit board inside the magazine and then loads it to the PCB loader. On the other hand, the loader sends the print circuit board onto the Stencil Printer.

Screening of the SMT Solder Paste (by solder paste printer)

After entering this stage, the very first step is to solder up the bare print circuit board. The stencil, which was built in the fabrication stage, is the first component that connects to the print circuit board in this stage. The stencil leaves pads which SMT equipment utilizes to mount components onto the PCB Board.

Component Placement (by the pick and place equipment)

When the soldering process is complete, the print circuits board moves on to the next stage, which is the component placement. Here a pick and place machine picks up components and mounts them onto PCB according to their associated pads. You should note that this process is entirely automatic to reduce errors.

When this stage is over, the PCB moves on to the reflow soldering phase to enhance the components attachment to the PCB.

X-Ray Inspection (done by the SMT X-ray Equipment)

When the reflow cycle is over, any PCB having QFN, BGA, or any other lead-less packages moves on to the X-Ray inspection.

The X-Ray inspection stage helps operators detect any issues in the PCB’s assembly process.

Wave Soldering (done by the wave soldering equipment)

In this stage, the board moves via a conveyer through a molten solder “wave.” The solder, in this case, bonds together any leads and component pads that are not well covered.

Final Inspection

Intermediary inspection cannot confirm the actual quality of the complete electronic device. Hence there must be a final inspection stage to thoroughly inspect the complete PCB.

The final inspection stage involves:

  • Visual inspection
  • Automated optical inspection
  • Functional Circuit Testing
  • In-circuit testing

Summary of main SMT Line Equipment

Here is the main SMT line equipment that sees through the processing of PCBs:

Pick and place machine

These machines mount components accurately onto PCBs

Solder paste Mixer

It mixes solder paste and solder powder evenly to help achieve perfect reflow effects and printing.


Bakes print circuit boards to remove moisture from the board.

SMT Loader

Places print circuit boards inside the racks of the solder printing machine.

Solder Paste Printing Machine

Prints solder paste onto bare PCBs.

SPI machine

It checks on the volume distribution, area, and thickness of the solder paste that is printed onto the bare PCB surface.

Reflow Machine

The reflow machine melts the solder bond between components and circuits. It then cools the bond to form a firm and conductive electric connection.


AOI machines detect placement failures

Docking Station

Acts as a station for connection between various machines

SMT Unloader

Receives and then stores PCBs after the reflow soldering stage


SMT has become a cornerstone for innovation in the modern world. In this time and age, most people want slick slim gadgets, and that is what SMT provides. However, to achieve these thin gadgets, many processes have to take place. We hope that this article has given you an insight into the processes that occur during SMT line processing plus the equipment in use.




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