Exploring the Distinctions between SMT and THT in PCB Assembly

SMD assembly (SMT assembly and THT assembly) refers to placing components with sheet structure or miniaturized components suitable for surface assembly on the surface of the printed board according to the requirements of the circuit, and assembling them by soldering processes such as reflow soldering or wave soldering, And then used in the production of finished products. So, what’s the difference between SMT and THT?

SMT is a surface mount technology, and THT is a traditional through-hole mounting technology. From the perspective of SMD assembly technology, the fundamental difference between SMT and THT is “Mounting” and “Plugging”. On the THT circuit board, components and solder joints are located on both sides of the board respectively; On the SMT circuit board, solder joints and components are on the same side of the board. Therefore, on SMT circuit boards, through holes are only used to connect wires on both sides of the circuit board, and the number of holes is much less and the diameter of holes is much smaller. In this way, the assembly density of the circuit board can be greatly improved.
First, SMT packaging its advantages:

• Effectively saving PCB area;
• Providing better electrical performance;
• Protect the internal parts of components from environmental influences such as humidity;
• Provide good communication;
• Help heat dissipation and provide convenience for transmission and testing.

Second, compared with THT, SMT has the following advantages:

1. Realize miniaturization. SMT electronic components, their geometric size and space occupied volume are much smaller than through-hole plug-in components, which can generally be reduced by 60% ~ 70%; The weight is reduced by 60% ~ 90%.
2. The signal transmission speed is high. SMT has a compact structure and high assembly density, which can reach 5.5 ~ 20 solder joints/cm. Due to the short connection and small delay, high-speed signal transmission can come into reality; At the same time, it is more resistant to vibration and impact. This is of great significance to the ultra-high-speed operation of electronic equipment.
3. Good high-frequency characteristics. Because the components have no leads or short leads, the distribution parameters of the circuit are naturally reduced and the radio frequency interference is reduced.
4. It is beneficial to automatic production and improves yield and production efficiency.
5. The material cost is low. The packaging cost of most SMT components is lower than that of iFHT components of the same type and function. Subsequently, the sales price of SMT components is lower than that of THT components.
6. SMT technology simplifies the production process of the whole machine product, reduces production costs, and improves production efficiency. The processing cost of functional circuits is lower than that of through-hole insertion, which can generally reduce the total production cost by 30% ~ 50%.