SMD: It is an abbreviation of Surface Mounted Devices. It is one of Surface Mount Technology (SMT) components. In the initial stage of circuit board production, through - hole assembly is completely manual. When the first automated machines were introduced, they could place some simple pin elements, but complex elements still needed to be placed manually for reflow soldering. Surface Mounted Components mainly include rectangular chip components, cylindrical chip components, composite chip components and special-shaped chip components