With the development of science and technology, electronics are developed in the direction of being small, thin, light and digital. Correspondingly, components are becoming miniaturized, flaked and compounded. These components that don’t have pins or have short pins are mounted on the surface of the PCB, and thus they are called SMD(Surface Mount Device). This technology adopted to mount these components is called SMT(Surface Mount Technology). SMDs are accurately fixed on the PCB with glue or solder and then are soldered by hot-blast stove. Because of the small volume of SMD, there is no need to drill for these components. The density of mounted components increases a lot, which makes the cost of tin or auxiliary materials used and the time spent decrease correspondingly. Compared to THT(Through Hole Technology) components, SMT components can decrease the area and the weight of the assembled PCB a lot. The cost of SMT would be 60%-70% less than that of THT.
The SMT process includes pre-heating, heat preservation, reflow and cooling. The aim of pre-heating is to make the temperature counterbalanced and stable. The temperature of the heat-preservation room shall be ensured to be 180℃ and the temperature difference shall not be large; 40%-60% humidity is the most suitable. When heating, the heater is generally set to be 245℃. The melting point of solder is 183℃.