SMT Assembly


SMT, or Surface Mount Technology, is an advanced technology for assembling electronic circuits by which components are mounted directly on the surface of a PCB. In addition to the different assembly methods, there are also differences in the components used. Generally, the components using SMT technology are patch components, which are smaller in size and have powerful functions. The integrated circuits (ICs) we often say are mounted on circuit boards through this process.


The SMT process involves several steps, including solder paste printing, pick and place, soldering, and inspection. Solder paste is applied to the PCB, and components are then precisely placed using a pick and place machine. After placement, the board goes through a soldering process, where the components are permanently affixed to the board. Finally, the board is inspected to ensure that all components are properly mounted and functioning.


SMT assembly has revolutionized the electronic industry with its ability to increase efficiency and reduce costs. You can find that the electronic products used in daily life are getting smaller and smaller, such as 0.1mm computer monitors, mobile phones with the same thickness as coins, etc. Although these electronic products are getting smaller in size, their functions are more powerful. All this is due to the application of SMT assembly in PCBA processing. The components used in SMT assembly are much smaller than traditional components, allowing for the creation of smaller and more powerful electronic devices.


One advantage of SMT assembly is its ability to automate the assembly process. SMT offers many advantages over through-hole technology, including higher component density, lower cost, and improved electrical performance. It has become the most widely used technique in PCB assembly and is used in a wide variety of electronic devices including smartphones, computers and televisions. This leads to faster and more efficient assembly, reducing costs and increasing productivity. Additionally, SMT assembly produces less waste and requires less material, making it a more environmentally friendly option.

Soldering Technology

Soldering is a critical process in electronic manufacturing that involves melting a metal alloy to join two metals. This process is used to create a strong and reliable connection between electronic components and a printed circuit board. There are several types of soldering techniques used in electronic manufacturing, including manual welding, wave soldering, and reflow soldering.

Manual Welding

Manual welding is the most basic and commonly used soldering technique. As the name suggests, it is done manually, making it suitable for small-scale PCB assembly or for hobbyists who want to customize their circuit boards. In manual soldering, a soldering worker uses a manual soldering pen and solder wire to attach electronic components to a circuit board. Hand soldering requires a high degree of skill and experience and requires good eyesight and hand coordination.

The manual welding process includes the following steps:

  1. Prepare tools and materials, including solder wire, hand soldering pen, and circuit board.
  2. Heat the solder wire and melt it, apply the solder to the parts that need to be soldered.
  3. Insert the electronic components into the solder and wait for the solder to cool.
  4. Clean the welding area to ensure welding quality.

Wave Soldering

Wave soldering is a method of using large advanced equipment to complete the welding work, making it suitable for mass production. In wave soldering, a solderer places electronic components on a circuit board and then passes the board through a bath of solder. The molten solder in the solder bath connects the electronic components to the circuit board.

The wave soldering process includes the following steps:

  1. Prepare tools and materials, including a solder bath and circuit board.
  2. Place the electronic components on the board and pass the board through the solder bath.
  3. The molten solder in the solder bath connects the electronic components to the circuit board.
  4. Clean the welding area to ensure welding quality.

Reflow Soldering

Reflow soldering is used to permanently fix the components on the board during the SMT assembly process. This process can apply melted solder paste to component pins and circuit board pads by heating at high temperature, and then melt and re-solidify at high temperature to form a reliable solder joint connection.

The reflow soldering process includes the following steps:

  1. Place the components correctly on the board, which is usually done by an automatic pick and place machine.
  2. Apply a layer of solder paste to the circuit board so that it can form a reliable connection between the component pins and the pads when soldering.
  3. Preheat to ensure that the solder joints are evenly heated.
  4. When the board is preheated to the proper temperature, it needs to be put into a reflow oven for reflow soldering.
  5. When the soldering is done, the board needs to be cooled. The board is removed from the reflow oven and placed in a cooling zone to ensure even cooling of the solder joints.

Through-Hole Assembly Technology

Before the popularity of SMT technology, the most commonly used process in PCBA was through-hole assembly technology (THT). As the name suggests, this assembly method involves drilling holes on the bare PCB, inserting the pins of the components into the holes, and then permanently soldering them to the board. As the trend of miniaturization continues to grow, the use of through hole PCB assembly has decreased significantly. However, this technology is still used for some relatively expensive components or circuit boards that require frequent replacement of components.

The following is the basic process of through-hole assembly technology:

  1. Prepare tools and materials, including circuit boards, components, solder wires, solder paste, printing templates, drills, etc.
  2. Make a printing template. The stencil should have a pattern on which the metal foil forms the copper coating corresponding to the component pins.
  3. Drill holes on the circuit board. The location and number of drilled holes should match the location and number of component pins. After finishing, the board surface needs to be cleaned to remove tin shavings and other impurities.
  4. Apply solder paste to the board. This can be done with a printed template. Apply the solder paste on the stencil, then scrape off the excess solder paste with a scraper, leaving only the part corresponding to the component pins.
  5. Install components. Insert the pins of the components into the corresponding holes on the board. By flipping the board, the components are placed in the correct position.
  6. Welding. Using a soldering iron or a wave soldering machine, connect the pins of the component to the copper finish on the board. During the welding process, temperature and time need to be controlled to ensure the quality of solder joints.
  7. Testing. After the through-hole assembly is complete, the board needs to be tested to ensure that the components are working properly.

Hybrid technology

As the name suggests, mixed assembly and using both SMT and THT on one PCB board, the functions of modern electronic products are very strong, which means that the traditional SMT and THT cannot meet the needs, and it is necessary to combine the two on one board. This technology It is usually used to design more complex circuit boards, where it is necessary to use THT technology to assemble some larger or more complex components, and use SMT technology to assemble smaller or tighter components. For example, power supply and communication circuits usually use THT technology, while components such as processors and memory use SMT technology.

To achieve a successful hybrid assembly, there are several factors that need to be considered, such as the PCB layout, the choice of components, and the assembly process. Here are the basic steps for a hybrid assembly:

  1. PCB design: The PCB design needs to consider the layout of both SMT and THT components, ensuring that there is enough space for THT components, and that SMT components are placed in a way that optimizes the routing of traces.
  2. Component selection: The selection of components is critical for a successful hybrid assembly. It is necessary to choose components that are suitable for the assembly process and that can meet the requirements of the design.
  3. Assembly process: The assembly process for hybrid technology is more complex than for SMT or THT technology. It usually involves several steps, including drilling holes for THT components, applying solder paste for SMT components, placing components, and soldering.
  4. Inspection and testing: After the assembly is complete, it is necessary to inspect and test the board to ensure that all components are properly placed and soldered, and that the board functions correctly.

A few considerations for PCB assembly projects:

PCB assembly is a complex process that requires professional skills and advanced machinery. Therefore, choosing a reputable PCBA processing factory is essential for guaranteeing the success of your project.

PCBA projects typically involve large quantities and long-term cooperation, with orders ranging from tens of thousands to hundreds of thousands of dollars. Therefore, it is necessary to manufacture PCBA prototypes to test the service provider's abilities and ensure the circuit is functional.

Prototyping must choose a turnkey project

Optimizing your PCB design can save both time and money. Whenever possible, it is best to utilize the services of a professional EMS provider. Even if you don't require their design services, their engineers can review your designs to ensure they are manufacturable.

It is crucial to follow various rules, such as compliance with ISO or IPC standards, which play a vital role in creating manufacturable new products. Engineers must strictly adhere to design specifications and understand design rules.