Surface-Mount Technology

Surface-mount technology, known as SMT and originally called planar mounting, is a method of mounting electrical components directly onto the surface of a printed circuit board rather than through drilled holes; a component mounted this way is called a surface-mount device. It has largely replaced through-hole construction across industry because it allows for greater manufacturing automation, which lowers cost and improves quality, and because it lets more components fit onto a given area of board, though both technologies are often used on the same board, with through-hole mounting reserved for parts unsuited to surface mounting, such as large transformers and heat-sinked power semiconductors. A surface-mount component is typically smaller than its through-hole counterpart, since it has shorter leads or none at all, and may terminate in short pins, flat contacts, a matrix of solder balls known as a ball grid array, or terminations built directly onto the body of the component.