There are two main mounting schemes for placing components on a printed circuit board (PCB): through-hole technology (THT) and surface-mount technology (SMT). Given its popularity over the last few decades, it’s no surprise that designers default to SMT, but there are advantages to both schemes that are worth exploring, especially for high-reliability application designs.
Through-Hole Technology vs. Surface-Mount Technology
THT, also known as through-hole mounting (THM), is a mounting scheme where leads on an electronic component are inserted into pre-drilled holes on a PCB. The leads are soldered to pads on the opposite side of the board. There are two main types of THTs distinguished by their lead connections: axial and radial. Axial leads run through the component in a straight line, and each end of the lead wire attaches to another component. Axial leads offer a lower-profile configuration. Alternatively, radial leads protrude from one side of the component, taking up less board space because of their perpendicular positioning. These differences are important when assessing board geometry requirements and size constraints for your application.