PCB assembly SMT process detailed
Surface Mounted Technology (SMT) is a circuit mounting technology that directly mounts pin-free or short-lead surface assembly components (SMC/SMD, that is, chip components) on the surface of the PCB(printed circuit board) and realizes welding assembly by reflow welding or dip welding. The following is a detailed introduction to the PCB assembly SMT process:
First, the basic flow of SMT SMT process
Incoming material inspection
Check the PCB board to see if there are deformation, scratches, short circuit, open circuit and other problems, and check whether the solder resistance layer and screen printing layer meet the requirements.
Test the appearance, size, and coplanarity of the electronic components to ensure their quality. It is also necessary to sample 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, the appropriate solder paste template is selected and installed on the solder paste press.
Use the solder paste press to evenly print the solder paste on the pad of the PCB board. During the printing process, the thickness, shape and printing position of the solder paste should be precisely controlled to ensure that the solder paste can be accurately covered on the pad, and there are no defects such as less tin, more tin, pinching, and offset.
After printing, you can use SPI(Solder Paste Inspection, solder paste thickness gauge) and other equipment to detect the solder paste printing quality.
Component mounting
According to the pre-prepared program, the SMT machine picks up the corresponding surface mount components from the material belt or tray and accurately mounts them to the specified position of the PCB board.
In the mounting process, pay attention to the polarity and direction of the components to ensure correct mounting. For some small components, such as 0201, 01005 and other packaged components, the mounter needs to have higher accuracy and stability to ensure the mounting quality.
Reflow welding
The mounted PCB board is sent into the reflow welding furnace and welded under a certain temperature curve.
The reflow welding process usually includes preheating, constant temperature, reflow and cooling. In the preheating stage, the solvent in the solder paste can be volatilized to avoid bubbles during reflow welding. The temperature of the reflux stage should ensure that the solder paste is completely melted to form a good welding connection; In the cooling stage, the solder joint should be cooled rapidly, the welding structure should be solidified, and the welding strength should be improved.
The temperature curve setting for reflow welding should be optimized according to the component type and board material to avoid overheating or insufficient welding or component damage.
Quality inspection
Using visual inspection, automatic optical inspection (AOI), X-ray inspection, online tester (ICT), flying needle tester, function tester and other inspection methods, the welding quality and assembly quality of PCBA(printed circuit board components) are comprehensively tested.
Visual inspection is mainly to manually observe the PCBA surface to check whether there are obvious defects such as missing components, offset, short circuit, and virtual welding.
AOI uses the optical imaging principle to quickly scan PCBA, detect welding defects, and automatically judge and mark them through image analysis software.
X-ray inspection is mainly used to detect welding defects hidden inside components such as BGA(ball grid array).
Rework with splitter
For detected defective products, use tools such as soldering iron and repair workstation to repair them, remove the bad welding spots, and weld them again to ensure that the product quality meets the requirements. After the repair, it is necessary to test again until the quality of the product is qualified.
Multiple PCBS are separated from the mother board, usually using a V-CUT or punching machine for board splitting operations.
Grinding board and washing board
The PCB that has been divided needs to be ground and washed to remove excess burrs and residues and ensure the clean and smooth surface of the board.
Second, the characteristics and advantages of the SMT patch process
High assembly density
SMT technology can achieve higher assembly density, so that the PCB board can accommodate more functional modules, so as to achieve the miniaturization and multi-functional products. For example, the various chips and components densely arranged on the smart phone motherboard are thanks to SMT technology to achieve powerful functions in a limited space.
High production efficiency
SMT technology has a high degree of automation, can quickly and accurately complete the mounting of a large number of components, greatly shortening the production cycle of products, reduce production costs.
High reliability
SMT patch technology uses surface-mount components that have short pins, small size, light weight, and fewer welding points, thus providing higher reliability. In addition, SMT technology also reduces electromagnetic and RF interference and improves product stability.
Easy to automate production
SMT technology can be combined with automated production equipment to achieve fully automated production lines and improve production efficiency and product quality.
Third, the application field of SMT patch process
SMT technology is widely used in various consumer electronics, communication equipment, industrial control, automotive electronics, aerospace and many other fields. With the continuous development and upgrading of electronic products, SMT chip technology is also constantly improving and improving, providing strong support for the miniaturization, multi-function and high reliability of electronic products.
Fourth, the development trend of SMT SMT process
Miniaturization and high precision
With the continuous miniaturization of electronic products, SMT chip technology will also develop in the direction of miniaturization and high precision. Future SMT equipment will have higher mounting accuracy and stability, and will be able to handle smaller and more precise components.
Intelligence and automation
SMT technology will be combined with intelligent and automated technology to achieve fully automated and intelligent production of the production line. By introducing advanced technologies such as artificial intelligence and big data, production efficiency and product quality can be improved and production costs reduced.
Green and environmental protection
With the continuous improvement of environmental awareness, SMT technology will also develop in the direction of green and environmental protection. Future SMT equipment will use more environmentally friendly materials and processes, reducing the impact on the environment.
In summary, SMT SMT process as the most widely adopted in the electronic assembly industry of an advanced process, with high assembly density, high production efficiency, high reliability, easy to achieve automated production and other advantages, widely used in all kinds of electronic products. With the continuous progress and improvement of technology, the SMT patch process will continue to play an important role in the future.
