Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). The PCB industry has largely replaced the thru-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the thru-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.
An SMT component is usually smaller than its thru-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component.