PCB Assembly SMT SMT process details

Table of Contents

PCB assembly SMT SMD process details

SMT (Surface Mounted Technology, Surface Mount Technology) is a pinless or short lead surface assembly components (SMC / SMD, that is, sheet components) directly mounted on the surface of the PCB (printed circuit board), and through the re-flow soldering or dip soldering and other methods to achieve the soldering and assembly of the circuit mounting technology. The following is a detailed introduction to the PCB assembly SMT SMD process:

First, the basic flow of the SMT placement process

Incoming material inspection

Inspection of the PCB board, to see if there is deformation, scratches, short circuit, open circuit and other issues, while checking the solder resist layer, silk screen layer and so on whether it meets the requirements.

The appearance, size, pin coplanarity of electronic components are tested to ensure that their quality is qualified. It is also necessary to sample test the electrical performance of the components to ensure that they meet the design requirements.

Solder Paste Printing

According to the design of the PCB board and the specifications of the components, a suitable solder paste stencil is selected and installed on the solder paste printing machine.

Using the solder paste printing machine, print the solder paste evenly on the pads of the PCB board. During the printing process, the thickness, shape and printing position of the solder paste should be accurately controlled to ensure that the solder paste can accurately cover the pads and there are no defects such as less solder, more solder, pulling tip and offset.

After printing, you can use SPI (Solder Paste Inspection) and other equipment to test the quality of solder paste printing.

Component placement

Mounter according to the pre-programmed program, from the material belt or tray to pick up the corresponding surface mount components, and will be accurately affixed to the PCB board on the designated location.

During the mounting process, attention should be paid to the polarity and direction of the components to ensure correct mounting. For some tiny components, such as 0201, 01005 and other packages of components, the mounter needs to have higher precision and stability to ensure the quality of placement.

Reflow soldering

The mounted PCB boards are sent into the reflow oven to be soldered under a certain temperature profile.

The reflow soldering process usually includes preheating, constant temperature, reflow and cooling stages. Preheating stage can make the solvent in the solder paste volatilization, to avoid air bubbles in the reflow process; reflow stage temperature to ensure that the solder paste is completely melted, the formation of a good welding connection; cooling stage to make the solder joints cooled quickly, curing the weld structure, improve the strength of the weld.

The temperature profile setting of reflow soldering should be optimized according to the component type and board material to avoid overheating or underheating resulting in weak soldering or component damage.

Quality Inspection

Visual inspection, automatic optical inspection (AOI), X-ray inspection, in-circuit tester (ICT), flying probe tester, function tester and other inspection means are used to comprehensively inspect the soldering quality and assembly quality of PCBA (printed circuit board assembly).

Visual inspection is mainly through manual observation of the PCBA surface to check whether there are components missing, offset, short circuit, false soldering and other obvious defects.

AOI, on the other hand, utilizes the principle of optical imaging to quickly scan the PCBA, detect welding defects, and automatically judge and mark them through image analysis software.

X-ray inspection is mainly used to detect soldering defects hidden inside components such as BGA (Ball Grid Array).

Rework and Depaneling

For the defective products detected, the use of soldering iron, rework workstations and other tools for rework processing, to remove the bad welding points, re-welding, to ensure that the product quality meets the requirements. Rework need to be tested again, until the product quality is qualified.

Separate multiple PCBs from the motherboard, usually using V-CUT or punching and cutting machines for board separation operations.

Grinding and washing

After the partition of the PCB need to grind and wash board processing to remove excess burrs and residues, to ensure that the board surface is clean and smooth.

Second, the characteristics and advantages of SMT placement process

High assembly density

SMT placement technology can achieve a higher assembly density, so that the PCB board can accommodate more functional modules, thereby realizing the miniaturization and multifunctionality of the product. For example, the smart phone motherboard densely arranged on a variety of chips and components, it is thanks to the SMT placement technology to achieve a powerful function in a limited space.

High production efficiency

SMT placement technology has a high degree of automation, can quickly and accurately complete a large number of components mounted, greatly shortening the production cycle of the product and reduce production costs.

High Reliability

SMT placement technology uses surface mount components, which have shorter pins, smaller size, lighter weight, and fewer soldering points, and therefore have higher reliability. In addition, SMT placement technology reduces electromagnetic and radio frequency interference and improves product stability.

Easy to realize automated production

SMT SMD technology can be combined with automated production equipment to achieve fully automated production line, improve production efficiency and product quality.

Third, the application areas of SMT placement process

SMT placement technology is widely used in various types of consumer electronics, communications equipment, industrial control, automotive electronics, aerospace and many other fields. With the continuous development and renewal of electronic products, SMT placement technology is also progressing and perfect, for the miniaturization of electronic products, multifunctionality, high reliability provides strong support.

Fourth, the development trend of SMT placement process

Miniaturization and high precision

With the continuous miniaturization of electronic products, SMT placement technology will also be towards the direction of miniaturization and high-precision development. Future SMT placement equipment will have higher placement accuracy and stability, and can handle smaller, more precise components.

Intelligent and automation

SMT placement technology will be combined with intelligent and automation technology to realize fully automated and intelligent production lines. Through the introduction of artificial intelligence, big data and other advanced technologies, production efficiency and product quality can be improved and production costs can be reduced.

Greening and environmental protection

With the increasing awareness of environmental protection, SMT placement technology will also develop in the direction of greening and environmental protection. Future SMT placement equipment will use more environmentally friendly materials and processes to reduce the impact on the environment.

In summary, the SMT placement process as the electronic assembly industry in the most widely adopted an advanced process, with high assembly density, high production efficiency, high reliability, easy to realize the advantages of automated production, etc., widely used in various types of electronic products. With the continuous progress and improvement of technology, SMT placement process will continue to play an important role in the future.