SMT Assembly Process

Surface Mount Technology (SMT) Process

Printed Circuit Board Assembly (PCBA) is the process of producing circuit boards with electronic components attached to them. One of the most popular techniques for PCBA is Surface Mount Technology (SMT), which is universal in the electronic industry today. The SMT process involves placing electronic components directly onto the surface of the PCB, rather than inserting them into drilled holes, as is the case with through-hole technology. This process is faster, more efficient, and allows for the use of smaller and more densely packed components.

Trace the Lines

The SMT assembly process begins with the PCB itself, which is a thin board of a non-conductive material, such as fiberglass or plastic. Copper traces on the board serve as the pathways for electrical current. A photolithography process etches these traces onto the board, which involves exposing the board to light through a stencil called a mask to create the desired trace pattern.

Pick & Place

Once the PCB is ready, the next step is to place the electronic components onto the board. Automated pick-and-place machines quickly and accurately place small components, such as transistors and resistors, onto the board.

AO-I Must Inspect

After the component placement, the PCB goes through an Automatic Optical Inspection (AOI) process to ensure that the correct components end up in the correct locations and that there are no missing or incorrectly placed components. AOI uses high-resolution cameras to capture images of the PCB and compares them to a pre-defined image of the PCB, allowing it to detect any discrepancies.

Leave the Oven On!

The next step is soldering the components to the board to make electrical connections. A reflow oven melts a small amount of solder on the bottom of each component, allowing the machine to securely attach them to the board. In some cases, selective soldering comes into play, which involves selectively applying solder to specific areas of the PCB, rather than applying it to the entire board. This technique is particularly useful when working with complex or sensitive PCBs that require more precise soldering.

Test, Test, & Test

After the reflow process, the PCB goes through another round of AOI inspection to check the quality of the soldering. If there are any defects, the assembler will rework the PCB to correct the problem.

In some cases, the manufacturing process also includes X-ray evaluation, which is an additional step of quality control to ensure that the solder joints are properly formed. It also allows for checks for hidden defects, such as solder bridges or voids, that would not be visible in a visual inspection. X-ray inspection is particularly useful when working with dense or complex PCBs where it is difficult to visually inspect all the solder joints.

Cleaned & Packaged

After the AOI and X-ray inspection, the assembler may use the washer to clean the PCBA and then package it for shipping to the customer. If the PCBA is part of a larger product, the manufacturer will then integrate it into the final product, such as a computer or a mobile phone.


In summary, the PCB assembly process using Surface Mount Technology (SMT) includes several steps: PCB preparation, component placement, Automatic Optical Inspection (AOI), soldering, selective soldering, AOI inspection, X-ray evaluation, cleaning, and packaging. This process is efficient, and reliable, and allows for the use of smaller and more densely packed components. By including inspection steps such as AOI and X-ray evaluation, it ensures that the final product is of high quality and meets all the necessary requirements. With the advancement of technology, the SMT assembly process has become more efficient, accurate, and reliable; however, it still requires skilled labor and attention to detail to produce high-quality circuit boards.

It is important to use an experienced printed circuit board assembly (PCBA) manufacturer like PGF Technology Group to ensure that your PCBs are made to the highest quality standards and meet your specific requirements. With years of experience and state-of-the-art machinery, PGF Technology Group is well-equipped to handle all your PCBA needs. They have a team of experts who are knowledgeable in all aspects of the PCB assembly process, from design to manufacturing.


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