The widespread use of micro electronic products has promoted the development of SMC and SMD towards miniaturization. At the same time, some electromechanical components, such as switches, relays, filters, delay lines, thermistors, and varistors, have also achieved chip based design. The surface assembled components in PCBA processing plants have the following significant characteristics:

(1) On the electrodes of SMT components, some solder joints have no leads at all, while others have very small leads. The spacing between adjacent electrodes is much smaller than that of traditional dual inline integrated circuits, with a lead spacing of (2.54mm). The center to center distance of IC pins has been reduced from 1.27mm to 0.3mm; Under the same level of integration, the area of SMT components is much smaller than traditional components, and chip resistors and capacitors have changed from the early 3.2mm × Shrink from 1.6mm to 0.6mm × 0.3mm; With the development of bare chip technology, BGA and CSP high pin devices have been widely used in production

(2) SMT components are directly mounted on the surface of the printed circuit board, and the electrodes are soldered onto the solder pads on the same side of the SMT components. In this way, there are no solder pads around the through holes on the PCB printed circuit board, greatly increasing the wiring density of the printed circuit board.

(3) Surface assembly technology not only affects the area occupied by wiring on printed circuit boards, but also affects the electrical performance of devices and components; Learning characteristics. Without leads or short leads, the parasitic capacitance and inductance of components are reduced, thereby improving high-frequency characteristics, which is beneficial for increasing usage frequency and circuit speed.

(4) Simple in shape, sturdy in structure, tightly attached to the surface of the PCB printed circuit board, improving reliability and seismic resistance; During assembly, there is no need to bend or cut wires. When manufacturing printed circuit boards, the through-hole for inserting components is reduced. The size and shape are standardized, and automatic mounting machines can be used for automatic mounting. This is efficient, reliable, and convenient for mass production, with lower overall costs.

(5) In a traditional sense, surface mounted components have no pins or short pins. Compared to plug-in components; The methods and requirements for solderability testing are different. The entire surface component can withstand higher temperatures, but the pins or endpoints assembled on the surface can withstand lower temperatures during welding compared to DP pins.

Of course, surface mounted components also have shortcomings. For example, sealed chip carriers are expensive and are generally used for high reliability products. They require matching with the thermal expansion coefficient of the substrate, and even so, solder joints are still prone to failure during thermal cycling; Due to the fact that the components are tightly attached to the surface of the substrate, the gap between the components and the PCB surface is quite small, making cleaning difficult. To achieve the purpose of cleaning, it is necessary to have good process control: the volume of the components is small, and the resistance and capacitance are generally not marked. Once they are messed up, it is difficult to understand; There is a difference in the thermal expansion coefficient between components and PCBs, which must be noted in SMT products.