Surface Mount Technology SMT PCB Assembly

JHYPCB provides one-stop service from PCB production, component procurement to Turnkey PCB assembly.

Printed Circuit Boards (PCBs) have changed the concept of soldering components with wire and creating a complicated and unreliable circuit. PCBs are very compact and offer reliable performance for a very long time. They take very little space and deliver the expected results.

Nowadays, PCBs are used in almost every industry. Every product that requires some components and their interconnection uses a PCB. PCBs have gone through many changes in the past few decades. There have been many advancements, improvements, and new technologies. One of the leading PCB technologies is the surface mount technology(SMT). It has supreme importance because it has further reduced the size of PCBs. The components used in the surface mount technology are very small; the smallest SMD (surface mount device) has a dimension of 0.6mm x 0.30mm. SMT technology has imposed a remarkable impact on the PCB industry, and it is widely used nowadays.

SMT PCB Assembly Supplier

We Provide one-stop SMT PCB prototype assembly to small and medium volume assembly services.

What is Surface Mount Technology (SMT)?

Surface Mount Technology (SMT) is a specific technology for PCBs. The components in this technology are directly mounted on the surface of the PCB without any holes/drilling. There are special components used for this technology that are called Surface Mount Devices (SMD). The components are placed over the PCB that already has conduction paths, and finally, the components are soldered in a reflow oven. They are directly attached to the board and provide better performance than Through-hole Technology (THT).

SMT is an easy and quick technique to make reliable circuit boards. The components are very compact, which is the reason the PCB is very small. Nowadays, SMT is widely used because it is a quick and better alternative to THT.

SMT Assembly

Difference Between SMT and SMD


Often buyers get confused with these two terms: SMT and SMD. These terms are often used interchangeably, but they are different.

SMT stands for Surface Mount Technology, a technology or a method of placing components directly on the PCB. On the other hand, SMD stands for Surface Mount Devices that are components or devices used in the Surface Mount Technology. The devices are components, such as resistors, transistors, and LEDs. Both terms have a relationship, but they refer to different things. Long story short, SMT is a process while SMDs are the physical components.

Difference Between SMT and THT

SMT and THT are two different technologies for mounting electronic components on the PCB board. Both are different and have their distinct advantages and disadvantages.

THT is old technology and was widely used before SMT. THT components are a bit large as compared to their SMT counterparts. Thus, a THT PCB assembly is a bit larger than an SMT PCB assembly. However, when the THT components are soldered, they can bear high mechanical and environmental stress. But SMT components cannot bear thermal and mechanical stress because they use less solder paste, which fails in the case of stress.

Nowadays, SMT is preferred over THT, but THT is still used where there is high heat and mechanical stress. There is also a Mixed technology that uses both SMT and THT. It is by far the best because the components suitable for SMT are placed via SMT and the others placed through THT. Such types of boards have the qualities of both technologies, making the PCB more reliable and cost-effective.

Through-Hole Technology PCB Assembly Componets

Benefits of SMT Technology

SMT PCB Assembly Equipment

The dominant benefit of surface mount technology is its compactness. It reduces the size of the PCB assembly and makes it lightweight. The component packages are very small; therefore, they take little space as compared to THT components. Furthermore, the components can be placed on both sides of the PCB. So, a large circuit can be made on a small board.

SMT offers reliable performance and optimum results. The process is carried out through machines, so the chances of errors are less. The soldering is also done by an automated process, so it is less prone to short circuits and other problems.

The cost of SMT PCB assembly is low because there is no need for holes. It saves time and effort, which reduces costs. Moreover, SMDs are small and can be transported easily. They require less space.

SMT reduces the time to assemble a PCB. There are surface mount technology machines that can place the component directly on the board. Moreover, there is no need for drilling, which also reduces the time. In the case of THT, most components are soldered manually or by other processes, but SMDs are picked and placed by machines and then soldered in the reflow oven. Almost every step is automated. Thus, the production of SMT PCB assembly is much faster than the THT PCB assembly.

Disadvantages of SMT

There is very little solder applied to the SMT PCB assembly. Therefore, it cannot bear thermal and mechanical stress. These solder joints are likely to fail in case of heat cycles. So, SMT is not reliable for extreme environments.

There are fewer chances of errors because of the automated process, but it is difficult to trace if there is any. Finding errors in SMT PCB assembly is not easy. It requires special techniques to find errors.

Surface mount technology requires expertise. There are trained people to carry out the process successfully. Moreover, the surface mount technology machinery is quite expensive.

SMT PCB Assembly Machine

Surface Mount Technology Assembly Process

The process of surface mount technology involves some important steps. It starts all the way from PCB designing and ends at the final testing of PCBA.

SMT PCB assembly process Flow chart
SMT PCB Assembly Manufacturing Process

1) PCB Designing

PCB designing is the responsibility of the buyer. He needs to design the PCB according to the requirements. During designing, appropriate SMDs are selected. PCB substrate, number of layers, solder mask, silkscreen, and everything is chosen. After designing, Gerber files, BOM, and other important files are provided to the PCB manufacturer. From this stage, the work of the PCB manufacturer starts.

PCB Design

2) Design for Manufacturability (DFM) Inspection

Most designers are not aware of the PCB assembly process. So, they don’t understand the technicalities and complications. This is the reason their design could have some problems. But DFM inspection is carried out at our end. Our experts check the files provided by the customer and ensure everything is up to the mark. It reduces delays in the manufacturing process.

DFM check is an essential step because the errors and problems are detected before the start of manufacturing. These problems are solved after consulting the customers. After that, the manufacturing process is carried out smoothly. Not only the delivery time is ensured, but the manufacturing cost is also reduced.


3) Component Procurement

The components are bought according to the BOM. So, BOM is an essential document for PCBA. If there is something unavailable, the component could be replaced with a similar one after consulting the buyer. The components are shipped from different vendors, so this step requires a few days.

PCB Assembly Components

4) PCB Fabrication

The procurement of components requires time. Until then, the PCB is fabricated. The bare board is fabricated according to the requirement of the buyer. These requirements are discussed at the time of placing the order. The buyer needs to provide the design and discuss the type of PCB base material, surface finish, solder mask, silkscreen, etc.

PCB Fabrication

5) Application of Solder Paste

For soldering the SMDs, solder paste is applied. The paste is applied to the required areas of the board only. Therefore, a stainless-steel stencil is used. The stencil is placed over the board, and solder paste is applied over it. The paste enters every hole of the stencil and covers the required area. Once you remove the stencil, you have solder paste in the required locations.

SMT Solder Paste Printing

6) Pick and Place

This is an automated process of picking and placing the SMDs on the PCB. The PCB is held in a machine, and the components are picked and placed in specific places. This automatic process makes the manufacturing process quicker. There is no need to place and solder the components manually. The process is done with the help of a robotic arm, so it can be carried out round the clock. It also reduces the probability of errors.

The components are placed where they should be. The XY coordinate of the components is provided using the Pick and Place file.

SMT Pick and Place Machine

7) Reflow Soldering

In pick and place, the components are only placed in the right places. Then, they are soldered using reflow soldering. The PCB is passed through a reflow oven, which melts the solder paste and connects the SMDs to the board.

The PCB is placed over a conveyor belt and passed through the oven. So, there is no manual work needed. After passing through the hot oven, the PCB is cooled.

SMT Reflow Soldering Oven

8) Inspection

Inspection is an important step to make sure the PCB is up to the mark and ready to provide the desired results. The problem can be with soldering. There could be short circuits or open circuits. Therefore, inspection is necessary to detect the flaws and errors.

First, the inspection is carried out manually. This is not necessary, but some errors can be detected by the naked eye. After manual inspection, AOI (Automatic Optical Inspection) or X-ray Inspection is carried out.

Automatic Optical Inspection (AOI) is a quick method of detecting errors. There are cameras that visualize the PCB. The visual image can also be seen on monitors. The cameras are placed at different angles to analyze every part of the PCB. But this method cannot analyze the connections under the components. It cannot be used for the inspection of a multilayer PCB.

X-ray Inspection is an advanced method. It can be used to see the connections under the components and the layers of the PCB. X-rays pass through the board and provide a picture on the screen. It can detect minor faults in the PCBA.

Automatic Optical Inspection and X-ray Inspection

9) Final Test

After inspection, the PCBA is tested to check the results that it is offering. This is a functionality test that ensures the components are working as expected. It is the last process of the surface mount manufacturing process. After this, the PCBA is shipped to the customer.

SMT PCB Assembly FAQs

The PCB assembly pricing includes setup fee, stencil fee, assembly fee and components cost. We do not charge any other labor fees.

  • Gerber file, it is used for PCB production.
  • BOM file(Bill of Materials).
  • CPL file(Component Placement List / Pick & Place File (PNP) file), it is used by our automated SMT Assembly machines to determine where each part should be located on the board.

Send Gerber file and BOM/CPL files to to get SMT PCB assembly quote.

No, you don’t have to. We’ll add fiducial marks for SMT assembly.

Assembly turn-time begins immediately after the PCB turn-time and 90% of SMT orders can be finished within 24 hours, 48 hours at most. We prepare all necessary material for SMT assembly like SMT engineering data, components and solder paste stencil while PCB production, so assembly can begin immediately after completing the PCB fabrication.

Order Your SMT PCBA Today!

JHY PCB is a PCB and PCBA manufacturing company based in China. We offer the best quality and fast turnaround without the restrictions of minimum orders. 

We are fully compliant with international standards. We are ISO, RoHS, and UL certified. Our strict quality management ensures high-quality PCB and PCBA. We can offer full turnkey SMT PCB assemblies. We also offer a DMF check to ensure timely delivery and a smooth manufacturing process. For more information, feel free to contact us.

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