How Does SMT Work?
Surface mount technology is the widely-used alternative to through-hole printed circuit board design and manufacturing practices. Today an increasing majority of PCB devices are available as SMDs or packages, making the adoption of SMT board designs and manufacturing practical and cost-effective.
In a simplified view of SMT manufacturing, fabrication generally consists of several highly-automated processes:
Board material contains solder pads without holes, to which solder paste is applied with a screen-printing-like process. Solder placement can be controlled through the use of a precise stencil template for the individual PCB being fabricated, to apply the material only where needed.
Automated component picking and placement machines then position the desired SMDs and other components on the boards precisely. Boards then continue to soldering operations which heat the solder pads to the point where the applied solder paste melts and bonds the components to the board.
Where heat-sensitive components are incorporated on the PCB, these may be installed after the automated soldering, either manually or through processes that would not damage the component. Boards are subsequently “washed” to remove excess flux or solder residues that could cause shorting of components due to their extremely close placement tolerance.
After that is the final inspection of quality including missing components, alignment issues, or soldering issues that could generate potential problems. Inspections of SMT boards can also be automated. Equipment is available that retains a visual image of the correct board construction, and compares the boards produced to the reference image.