Chip components are much smaller than the area and quality of conventional perforated components. In general, the use of SMT' reduces the volume of electronic products by 60% and the quality by '75%. Through-hole mounting technology components, they are mounted on a 2.54mm grid, while the SMT assembly component grid has grown from 1.27mm to the current 0.63mm grid, with individual 0.5mm grid mounting components for higher density. For example, a 64-pin DIP integrated block with an assembly area of 25mm × 75mm, and the same lead with a QFP with a lead pitch of 0.63mm, its assembly area is 12mm × 12mm, and the area is 1/12 of the through hole technology.
Due to the high reliability of the chip components, the device is small and light, so the seismic capacity is strong, the automatic production is used, the mounting reliability is high, and the general bad solder joint rate is less than 10 parts per million, which is better than the wave-hole soldering technology of the through-hole plug-in components. At an order of magnitude lower, the average MTBF of electronic products assembled with SMT is 250,000 hours. Currently, almost 90% of electronic products use SMT technology.
Since the chip components are firmly mounted, the devices 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 circuit designed by SMC and SMD has a maximum frequency of 3 GHz. The via components are only 500MHz. SMT can also be used to shorten the transmission delay time and can be used for circuits with a clock frequency of 16MHz or higher. With MCM technology, the high-end clock frequency of a computer workstation can reach 100MHz, and the additional power consumption caused by parasitic reactance can be reduced by 2 to 3 times.
·The printed board has a reduced area and the area is 1/12 of the through hole technology. If the CSP is installed, its area will be greatly reduced.
·The number of drilled holes on the printed board is reduced, saving the repair cost;
· Reduced circuit commissioning costs due to increased frequency characteristics;
· Due to the small size and light weight of the chip components, the packaging, transportation and storage costs are reduced;
· SMT and SMD are developing rapidly, and the cost is rapidly declining. A chip resistor has the same price as the through-hole resistor, which is about 1 cent.
At present, to complete the automation of the perforated printed board, it is necessary to enlarge the original printed board area by 40%, so that the insertion head of the automatic insert can insert the components, otherwise there is not enough space gap and the parts will be damaged. The automatic placement machine adopts a vacuum nozzle to absorb and discharge components, and the vacuum nozzle is smaller than the shape of the component, thereby increasing the installation density. In fact, small components and fine pitch QFP devices are produced by automatic placement machines for automated production across the board.
Of course, there are some problems in the large production of SMT, such as: the nominal value on the components is not clear, the maintenance work is difficult; it is difficult to repair and replace the device, and special tools are needed; the thermal expansion coefficient between the components and the printed board is poor. . However, these problems are all problems in development. With the advent of special disassembly and assembly equipment and the emergence of new low expansion coefficient printed boards, they are no longer an obstacle to the further development of SMT.