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SMT processing is the technology and process in PCBA processing
SMT processing is the most important process technology and process in PCBA processing. The improvement of SMT process flow and the development of technical solutions have a vital impact on electronic assembly processing. With the rapid development of science and technology, the process technology of the electronics industry has also made great progress. In order to make the products of the electronics industry more convenient for customers to carry, its volume is getting smaller and smaller, highly integrated, high-performance micro-electronic products It is loved by people. The SMT technology in the electronics industry is widely used. It has now replaced traditional electronic assembly technology in many fields, and is considered a revolutionary change in electronic assembly technology.
SMT screen printing process status
The so-called screen printing refers to printing solder paste on the PCB pads. The printing methods include contact-type stencil printing and screen printing without direct contact. SMT technology usually uses a contact method, so we are used to collectively refer to it as screen printing.
The first step of screen printing is to stir the solder paste. During the stirring process, attention must be paid to the viscosity and uniformity of the solder paste. The quality of viscosity has a direct effect on the quality of printing. Generally, the printing viscosity is stirred and determined according to printing standards. If the viscosity is too high or too low, it will affect the printing quality. The storage environment of solder paste requires a temperature of 0-5°C. Under this environment, the components in the solder paste will naturally separate. For this reason, during use, the solder paste should be taken out and placed at room temperature for 20 minutes to allow it to naturally heat up, and then stirred with a glass rod for 10-20 minutes; at the same time, the use of solder paste also has requirements for the environment, and its ideal environment The temperature is required to be maintained at 20-25°C, and the humidity is maintained between 40% and 60%.
Leaking solder paste on the PCB pads is the front-end work of SMT technology production, and makes sufficient preparations for the soldering of components. During the printing process, the squeegee pressure will push the solder paste onto the pads, and the thickness of the final screen should be controlled below 0.15mm. Practical results show that the silk-screen tin solder paste can not only improve the soldering quality, but also make the amount of solder paste on the PCB pads fuller.
Current status of component placement process
Mounting components is mainly for the assembly of components to be installed on the PCB position. During printing and production, the mounting components are different in form and position, so program coding must be done when installing them on the PCB position accurately. Whether the PCBA processing position is installed accurately depends on whether there are errors and loopholes in the coding process of the mounted components. If the staff does not check in place, it will easily lead to the printed board being discarded and cannot be used in production printing. When writing placement components, you should start programming based on a relatively simple structure, and then write more complex structure chip components. Only after reconfirming that there are no errors, can the production of placement start. In the next production work, the process is produced by automatic program. After the placement is completed, it is necessary to adjust the position and determine the direction, and at the same time, take effective measures to do laser recognition and camera recognition. Note that camera recognition is more suitable for mechanical structure, while laser recognition is widely used in the process of airplane flight, but this method is not suitable for BGA components.
Current status of reflow soldering process
Before putting the printed board into the reflow soldering, we need to check the direction and position of the components. Pay attention to temperature control during reflow soldering. Soldering usually needs to go through four steps of preheating, heat preservation, reflow and cooling to complete. The purpose of preheating is to ensure that the temperature is balanced and stable; the temperature of the holding room should be ensured at 180°C, and the temperature difference should not be too large; the moisture retention should be ensured at 40%-60% of the condition is the most appropriate. When PCBA is processed, note that the heater temperature is usually set to 245°C, and the melting point of the solder paste is 183°C. After being sent out of the reflow oven, the temperature of the PCB board will gradually cool down, allowing the solder joints to achieve the best results.
SMT technology development prospects and trends
At present, the competition between various industries in various countries in the world is becoming more and more fierce, and the cost pressure is relatively high. The SMT industry technology has shown its system integration in functions such as automatic intelligence, assembly, and logistics. With the advancement of science and technology, the degree of automation of SMT technology is getting higher and higher, labor costs are therefore greatly reduced, and personal output has therefore increased a lot. The main theme of the future development of SMT technology will be high performance, high flexibility, ease of use and environmental protection.
1. With the intensive development of the electronics industry, its competition is becoming more and more fierce, the increase in environmental protection requirements, and the development of the miniaturization trend of electronic products have all created higher requirements for SMT technology. High precision, high speed and high environmental performance are the mainstream trends in the development of SMT technology, and the placement head will also realize automatic conversion.
2. In the past few years, the SMT market has undergone many changes. Customers need to produce a variety of high-mix electronic products with small and medium-sized batches, instead of the previous market model of mass production. In addition, more and more people like wearable products, so we need to integrate more functions into the original smaller unit volume, and at the same time, to achieve assembly in a very small area, the technology will also increase. The more complicated. How to achieve high stability, high precision and relatively reliable printing and placement at high speed is a bottleneck in the development of SMT technology.
3. As the volume of electronic products shrinks and functions increase, component density will gradually increase. Now semiconductor manufacturers pay much attention to the application of high-speed placement machines, and SMT production lines will also be applied in some semiconductor integration areas. Therefore, the integration of semiconductor packaging technology and SMT technology is the development trend of the industry.
At present, China has become the world's largest SMT application country, but China is still lacking in cutting-edge electronics manufacturing, and often faces many problems in the application of new materials or process technology. Therefore, we need to increase our research on SMT technology to break through the bottleneck problem of China's cutting-edge technology of electronic products.
