Surface-mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards (PCBs) with solder paste. Electronic devices made this way are called surface-mount devices (SMDs). Surface-mount technology has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board.
An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all.
The three key steps in surface-mount technology are paste, place, and reflow.
In the first step, solder paste must be accurately placed onto a PCB with the aid of a stencil printer, which deposits the paste into the pattern of the circuit.
Next, the electronic components are precisely placed onto the board using a manual or automatic pick and place machine.
Finally, the solder paste must be heated until it melts and forms strong and reliable joints between the components and the surface of the board. This is accomplished through the use of a reflow oven which heats the solder to the proper temperature and then cools it down to a solid again.
