Surface mount technology (SMT) is a new generation of electronic assembly technology. It compresses traditional electronic components into components that are only a few tenths of the volume, thus realizing the high-density and high-density assembly of electronic products. High reliability, miniaturization, low cost, and production automation. The process of assembling these components on the circuit is called the SMT process, and the related assembly equipment is called SMT equipment. At present, advanced electronic products, especially computer and communication electronic products, have generally adopted SMT technology.
The assembly process of SMT and its process flow mainly depend on the type of surface mount component (SMA), the types of components used, and the conditions of SMT assembly equipment. In general, SMA can be divided into three types of single-sided mixed assembly, double-sided mixed assembly, and full-surface assembly, a total of six assembly processes. Different types of SMA have different SMT assembly processes, and the same type of SMA can also have different SMT assembly processes. Choosing an appropriate assembly method according to the specific requirements of the patch processing and assembly products and the conditions of the assembly equipment is the basis for efficient and low-cost assembly and production. It is also the main content of the SMT process design.
The characteristics of SMT process technology can be compared with the traditional through-hole insertion technology (THT). From the perspective of assembly process technology, the fundamental difference between SMT and THT is "sticking" and "inserting." The difference between the two is also reflected in all aspects of the substrate, components, component shape, solder joint shape and assembly process method.
THT uses leaded components. The circuit connection wires and mounting holes are designed on the printed board. The component leads are inserted into the pre-drilled through holes on the PCB, and then temporarily fixed, wave soldering is used on the other side of the substrate. The brazing technology performs welding to form reliable solder joints and establish long-term mechanical and electrical connections. The main components and solder joints are respectively distributed on both sides of the substrate. With this method, since the components have leads, when the circuit is dense to a certain extent, the problem of reducing the volume cannot be solved. At the same time, the faults caused by the proximity of the leads and the interference caused by the lead length are also difficult to eliminate.
The so-called SMT surface assembly technology refers to the chip structure components or the miniaturized components suitable for surface assembly, which are placed on the surface of the printed circuit board according to the requirements of the circuit, and assembled by soldering processes such as reflow soldering or wave soldering Together, it constitutes a certain function of electronic component patch processing and assembly technology.
The difference between SMT and THT component mounting and soldering methods: on the traditional THT printed circuit board, the components and solder joints are located on both sides of the board; while on the SMT circuit board, the solder joints and components are on the same board Surface. Therefore, on SMT printed circuit boards, through holes are only used to connect the wires on both sides of the circuit board, the number of holes is much smaller, and the diameter of the holes is much smaller. In this way, the assembly density of the circuit board can be greatly improved.
The advantages of SMT production line are as follows:
1. Small size and light weight
The volume and weight of SMT components are only about 1/10 that of traditional plug-in components, which is easy to mount. Generally, after SMT is used for processing, the volume of electronic products can be reduced by 40%-60%, and the weight can be reduced by 60%. ~80%.
2. Increased efficiency and reduced cost
SMT patch processing is easy to realize automation, improve production efficiency, save materials, energy, equipment, manpower, time, etc., and reduce costs by 30% to 50%.
3. High reliability, strong earthquake resistance. Good high frequency characteristics, reducing electromagnetic and radio frequency interference. Low solder joint defect rate. As is the case with all manufacturing processes, there are some disadvantages to SMT assembly. The biggest is that it requires a much higher attention to detail than through-hole assembly. Even with the process largely automated, your design parameters still have to be met to produce a quality end product. This largely falls on the shoulders of the designer and the electronics contract manufacturer.