surface-mount
Of electronic components, able to be soldered on top of printed circuit boards.
surface-mount: soldering parts flat onto circuit boards
Surface-mount technology places electronic components directly onto the flat surface of a printed circuit board (PCB) rather than inserting component leads through drilled holes. The component sits on exposed copper pads, and solder reflow bonds it in place. This differs from through-hole mounting, where leads pass through the board and are soldered on the reverse side.
Surface-mount components are typically much smaller than their through-hole equivalents. A 0603 resistor, for example, measures 0.06 by 0.03 inches and weighs under a tenth of a gram. Capacitors, inductors, integrated circuits in ball grid array (BGA) packages, and even connectors all have surface-mount versions. The components themselves are designed with flat terminations: flat pads on resistors and capacitors, gull-wing leads on small outline integrated circuits (SOIC), or solder balls on BGAs.
Manufacturing uses automated pick-and-place machines to position thousands of components per hour with high precision, typically within 0.1 millimeter. A reflow oven then heats the entire board to melt solder paste (usually a lead-free alloy such as SAC 305: tin, silver, and copper) and create the joints. This process is faster and more reproducible than hand soldering, making surface-mount essential for high-volume production.
Trade-offs and constraints
Surface-mount boards pack more components into less space and cost less to manufacture at scale. However, they are harder to repair by hand, require precision equipment and solder paste, and demand careful control of reflow temperature profiles to avoid damage to components or the board substrate. Thermal stress can crack solder joints over many heating cycles, so vibration-prone applications or boards subjected to extreme temperature swings need careful design.
The term gained currency in the 1980s as manufacturers sought to reduce board size and assembly cost. Today, surface-mount dominates consumer electronics, telecommunications, automotive, and industrial control. Through-hole components persist only where mechanical strength, easy field repair, or high current handling justify the larger footprint.