Definition of SMT surface technology
Modern high-performance electronic products generally rely more and more on the rapid development of computer technology, the popularization of LSI (Large Scale Integrated Circuit), VLSI (Very Large Scale Integrated Circuit) and PCB (Printed Circuit Board). At the same time, the requirements for PCB are getting higher and higher. The chipization and miniaturization of electronic components provide the possibility of high-density assembly.
SMT (Surface Mount Technology) is an electronic assembly technology that attaches and solders SMC (Surface Mount Components) and SMD (Surface Mount Devices) to the specified positions on the surface of the assembly substrate with PCB. The PCB used does not need to drill insertion holes, as shown in Figure 1-1. From a process point of view, first apply solder paste on the PCB pads, and then accurately place the surface mount components on the solder paste-coated pads, by heating the PCB until the solder paste is melted, and it will be achieved after cooling. The interconnection between components and printed circuits.
It can be said that SMT is a systematic comprehensive technology including electronic components, assembly, equipment, welding methods and assembly auxiliary materials. It breaks through the traditional printed circuit board through-hole substrate insertion method, and is here The new generation of assembly method developed on the basis is the most popular new concept of electronic assembly. It is also the electronic product that can effectively achieve “light, thin, short, small”, multi-functional, high-reliability, high-quality, low-cost One of the main means. SMT components and their assembly technology are rapidly entering various electronic products, and are gradually replacing the current through-hole substrate insertion method, becoming a new pillar manufacturing process of PCB and spreading to the entire electronics industry. Today, SMT has been widely used in the assembly of electronic products in various fields, such as aviation, aerospace, communications, computers, medical electronics, automobiles, cameras, office automation, and household appliances.
Surface assembly technology production line and its composition
The basic composition of SMT can be summarized into four parts: production materials, production equipment and production technology, and management. Among them, production materials and production equipment can be called SMT hardware, production process and management software called SMT. SMT involves chemical and material technology (various solder paste, flux, cleaning agent, various components, etc.), coating technology (application of solder paste or patch glue), precision machining technology (coating template production, tooling Fixture production, etc.), automatic control technology (production equipment and production line control), welding technology, testing technology, inspection technology and various management technologies, and many other technologies are a complex and comprehensive system engineering technology.
Features of surface mount technology
Compared with the way of through-hole inserting components, surface assembly technology has the following characteristics:
(1) Realize miniaturization. Surface mount electronic components, the volume can generally be reduced to 20% -30% of the through-hole plug-in components, the smallest can reach 10%, and the quality is reduced by 60% -80%.
(2) The signal transmission speed is high. Due to the compact structure, high assembly density, short wiring and low transmission delay, high-speed signal transmission can be realized. This is of great significance to electronic devices that operate at ultra-high speeds.
(3) Good high frequency characteristics. Since the components have no or short leads, radio frequency interference can be eliminated and the distribution parameters of the circuit can be reduced.
(4) Conducive to automated production, improving yield and production efficiency. Due to the standardization, serialization and uniform welding conditions of chip components, the surface assembly technology has a high degree of automation; the failure of components caused by welding is greatly reduced, thereby improving reliability.
(5) Simplify the production process and reduce the cost. When assembling on a printed circuit board, the leads of the components do not need to be bent or cut short, thus shortening the entire production process. The processing cost of the same functional circuit is lower than the through-hole assembly method.