Advantages of SMT surface mounting technology

Advantages of SMT surface mounting technology

As a new generation of assembly technology, SMT technology has only a history of more than 40 years, but this technology has fully demonstrated its strong vitality since its birth. It has completed the journey from birth, perfection to maturity at an extraordinary speed, and entered a prosperous period of large-scale industrial application. Today, both investment electronic products and civil electronic products have its shadow. Why does SMT develop so fast? This is mainly due to the following advantages of SMT.

1. High assembly density

The area and quality of chip components are greatly reduced compared with traditional perforated components. In general, the use of SMT can reduce the volume of electronic products by 60%~70% and the quality by 75%. Through hole installation technology is used to install components based on 2.54mm grid; The grid of SMT assembly components has developed from 1.27mm to 0.5mm at present, and the density of installed components is higher. For example, a 64 pin DIP integrated block has an assembly area of 25 mm × 75m, while QFP with lead spacing of 0.63mm is adopted for the same lead, and its assembly area is 12mm × 12mm, the area is 1/12 of the through-hole technology.

2. High reliability

Due to the high reliability of chip components, small and light components, it has strong seismic resistance. Automatic production can be used in electronic processing, with high mounting reliability. Generally, the rate of defective solder joints is less than 10 parts per million, an order of magnitude lower than the wave soldering technology of through hole plug components. The average MTBF of electronic products assembled with SMT is 250000 hours. At present, almost 90% of electronic products use SMT technology.

3. Good high-frequency characteristics

As chip components are firmly mounted, they are usually without leads or short leads, reducing the impact of parasitic inductance and capacitance, and improving the high-frequency characteristics of the circuit. The maximum frequency of the circuit designed with SMC and SMD is 3GHz, while the through hole components are only 500MHz. SMT can also shorten the transmission delay time, which can be used for circuits with clock frequency above 16MHz. If MCM technology is used, the high-end clock frequency of computer workstation can reach 100MHz, and the additional power consumption caused by parasitic reactance can be reduced to 1/3~1/2 of the original.

4. Reduce costs

The use area of the printed board is reduced, which is 1/12 of the through-hole technology. If CSP is used for installation, the area will be greatly reduced.

The number of holes drilled on the printed board is reduced, saving the repair cost.

Due to the improvement of frequency characteristics, the circuit debugging cost is reduced.

As the chip components are small in size and light in weight, the cost of packaging, transportation and storage is reduced.

SMC and SMD have developed rapidly, and the cost has dropped rapidly. The price of a chip resistor and a through-hole resistor is less than one cent.

5. Easy to automate production

At present, in order to achieve full automation of perforated installation PCB, 40% of the original PCB area needs to be expanded, so that the insertion head of the automatic plug-in can insert the components, otherwise there is not enough space clearance, and the components will be damaged. Automatic placement machine adopts vacuum nozzle to suck and place components. The vacuum nozzle is smaller than the shape of components, which can improve the installation density. In fact, small components and fine pitch QFP components are produced by automatic placement machine to achieve automatic production of the whole line.

Of course, there are also some problems in the SMT mass production, for example, the nominal values on components are not clear, which leads to maintenance difficulties and the need for special tools; Multi pin QFP is easy to cause pin deformation and lead to welding failure; The thermal expansion coefficient between components and printed boards is inconsistent, and the solder joint is subject to expansion stress when electronic equipment is working, resulting in solder joint failure; In addition, the overall heating of components during reflow soldering will also lead to thermal stress of components, which will reduce the long-term reliability of electronic products. However, these problems are all problems in development. With the emergence of special disassembly equipment and the emergence of new low expansion coefficient printed boards, they are no longer obstacles to the further development of SMT.