1:overview of SMT SMT is the abbreviation of Surface Mount Technology, which translates into surface mount technology. The United States is where SMT was invented. Since 1963, the first surface mount component appeared in the world and the first surface mount integrated circuit was introduced by Philips, SMT has been mainly used in cutting-edge products and investment products such as military, aviation and aerospace, and has gradually been widely used in computer, communication, military, industrial automation, consumer electronics and other industries. Surface mount technology has developed very rapidly. In 1980s, SMT technology became the hottest new generation of electronic assembly technology in the world, and was praised as a revolution of electronic assembly technology.

2.SMT composition: mainly composed of surface mount components (SMC/SMD), mounting technology and mounting equipment.

2. 1: surface mount component (SMC/SMD):

2. 1. 1: description of surface mount components (SMC/SMD): SMC: surface mount components, mainly referring to some active surface mount components; SMD: surface mount devices, mainly referring to some passive surface mount components;

2.1.2: the development trend of SMC/SMD;

(1): SMC chip components are developing in the direction of small and thin. Its size ranges from1206 (3.2mm *1.6mm) to 0805 (2.0mm *1.25mm)-0603 (1.6mm * 0.8mm)-0402 (/kloc)

(2) SMD surface mount devices are developing towards small, thin and narrow pin spacing. The pin center distance developed from 1.27 to 0.635 mm -0.5 mm -0.4 mm -0.4 mm and 0.3 mm. ..

(3) New packaging forms such as BGA (ball grid array), CSP(UBGA) and FILP chip (flip chip) have emerged. Because QFP (Square Flat Package Device) is limited by SMT process, the pin spacing of 0.3mm is already the limit. BGA pins are spherical and evenly distributed at the bottom of the chip. Compared with QFP, BGA has the following outstanding advantages: firstly, it has a high package area ratio of I/O number, which saves PCB area and improves assembly density. Secondly, the pin spacing is large, including 1.5mm, 1.27mm, 1.00mm, which makes the assembly difficult and the processing window large. Example: When the lead spacing of 3 1mm3 1mrBGA is 1.5mm, there are 400 solder balls (I/O); When the pin spacing is 1.0mm, there are 900 solder balls (I/O). It is also qfp-208,31mm * 31mm. When the pin spacing is 0.5mm, there are only 208 pins. BGA is very competitive in performance and price, and has always been in the leading position in high (I/O) device packaging. ?

(4) Narrow pitch technology (FPT) is the inevitable trend of SMT development. FPT refers to the technology of assembling SMD with pin spacing of 0.635-0.3mm and SMC with length * width less than or equal to 1.6 mm * 0.8 mm on PCB. Due to the rapid development of computer, communication, aerospace and other electronic technologies, the integration of semiconductor integrated circuits is getting higher and higher, SMC is getting smaller and smaller, and the pin spacing of SMD is getting narrower and narrower. At present, QFP with pin spacing of 0.635mm and 0.5mm has become a communication device in industrial and military electronic equipment.

2.2:SMT installation technology introduction:

2.2. 1:SMT assembly process type: single-sided/double-sided surface mounting, single-sided mixed mounting and double-sided mixed mounting.

2.2.2: Classification of welding methods: wave welding-plug-in welding (DIP) and partial patch welding (SMC/SMD). Reflow welding-heating methods include infrared, infrared heating wind combination, full hot air heating, etc.

2.2.3: printed circuit board: substrate material-glass fiber, ceramics, metal plate. Circuit board design-graphic design, wiring, gap setting, imposition, SDM pad design and layout.

2.2.SMT mounting equipment: screen printing machine, dispensing machine, mounter, reflow soldering, wave soldering, detection system and maintenance system.