surfacemounting

Surface mounting, or surface-mount technology (SMT), is a method for assembling electronic circuits in which components are mounted directly onto the surface of a printed circuit board (PCB). In SMT, most components have no long leads and are placed onto copper pads on the board, in contrast to through-hole mounting where leads are inserted into holes.

The standard SMT assembly process begins with applying a precise layer of solder paste to the PCB pads, typically through a stencil. Components are then picked and placed automatically by surface-m mount machines. The board passes through a reflow oven, where the solder paste melts and forms solder joints as it cools. Additional steps may include cleaning, inspection, and functional testing. Mixed-technology boards may use selective soldering for through-hole or larger components.

SMT supports a wide range of components and packages, including chip resistors and capacitors, and surface-mount devices such as SOIC, QFP, BGA, QFN, and CSP. Package sizes are standardized, with common small-form-factor codes such as 0402, 0603, and 0805 used for passive components. Modern boards often combine hundreds to thousands of SMT parts in high-density layouts.

Advantages of surface mounting include higher component density, smaller and lighter assemblies, and better suitability for automated, high-volume production. It enables shorter interconnects and improved electrical performance at high frequencies. Disadvantages include greater sensitivity to heat during soldering, potential solder joint defects, and repair or rework challenges for densely packed or hidden joints. SMT has become the dominant method for producing most contemporary electronics, from consumer devices to industrial systems.