PCBA Tech - About the benefits of SMT surface mount technology

Surface mount technology

1. High assembly density

The area and mass of chip components are greatly reduced compared to traditional perforated components. Generally, the use of SMT can reduce the volume of electronic products by 60% to 70% and the mass by 75%. Through-hole mounting technology is to install components according to a 2.54mm grid; while the SMT assembly component grid has evolved from 1.27mm to the current 0.5mm grid, and the density of installed components is higher. For example, a 64-pin DIP integrated block has an assembly area of 25mm*75m, and the same lead uses a QFP with a lead pitch of 0.63mm, and its assembly area is 12mm*12mm, which is 1/12 of the through-hole technology. .

2. High reliability

Due to the high reliability of chip components, small and light components, they have strong shock resistance. Automatic production can be used in electronic processing, and the placement reliability is high. Generally, the rate of defective solder joints is less than 10 parts per million. The wave soldering technology of hole-insertion components is an order of magnitude lower. The average MTBF of electronic products assembled with SMT is 250,000 hours. At present, almost 90% of electronic products adopt SMT process.

3. Good high frequency characteristics

Because the chip components are firmly mounted, the components are usually leadless or short leads, which reduces the influence of parasitic inductance and parasitic capacitance, and improves the high-frequency characteristics of the circuit. The highest frequency of the circuit designed with SMC and SMD is 3GHz, and The use of through-hole components is only 500MHz. The use of SMT patches can also shorten the transmission delay time, and can be used for circuits with a clock frequency of 16MHz or more. If the MCM technology is used, the high-end clock frequency of the computer workstation can reach 100MHz, and the additional power consumption caused by parasitic reactance can be reduced to 1/3 to 1/2 of the original.

4. Reduce costs

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

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

As the frequency characteristics are improved, the circuit debugging costs are reduced.

Due to the small size and light weight of chip components, the cost of packaging, transportation and storage is reduced.

SMC and SMD are developing rapidly, and the cost is falling rapidly. The price of a chip resistor and a through-hole resistor is already less than 1 cent.

5. Facilitate automated production

At present, if the perforated mounting printed board is to be fully automated, it is necessary to expand the area of the original printed board by 40%, so that the insertion head of the automatic plug-in can insert the components, otherwise there is not enough space and the components will be damaged. The automatic placement machine adopts a vacuum suction nozzle to suck and release the components, and the vacuum suction nozzle is smaller than the shape of the component, which can increase the installation density. In fact, small components and fine-pitch QFP components are produced using automatic placement machines to achieve full-line automated production.

Of course, there are also some problems in SMT production. For example, the nominal value on the components is not clear, which brings maintenance difficulties and requires special tools; multi-pin QFP is easy to cause pin deformation and cause welding failure; components and printing The thermal expansion coefficient between the boards is inconsistent, and the solder joints are exposed to expansion stress when the electronic equipment is working, which causes the solder joints to fail; in addition, the overall heating of the components during reflow soldering will also cause the thermal stress of the devices to reduce the long-term reliability of the electronic products. But 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.