throughhole

Through-hole refers to a method of mounting electronic components on a printed circuit board (PCB) in which the component leads pass through holes drilled in the board and are soldered to pads on the opposite side. This contrasts with surface-mount technology (SMT), where components are mounted directly on the PCB surface without through holes.

Common through-hole components include axial and radial leaded devices, dual-in-line packages (DIPs), transistors, capacitors, transformers, and terminal blocks. These parts have pins or leads that extend through holes in the PCB, which are then plated and soldered to copper pads or traces on the opposite side. Holes may be manually or automatically inserted and are designed to provide reliable mechanical and electrical connections.

The assembly process typically involves drilling or drilling-and-plating the holes, inserting components, and soldering. Soldering is often accomplished by wave soldering for tacked parts and larger assemblies, or by hand for prototypes and repair work. Through-hole assemblies are valued for their robustness and ease of inspection and rework.

Advantages of through-hole technology include strong mechanical bonding, good durability under vibration, and straightforward repair or replacement of components. It is also well suited for components with large or heavy leads and for applications requiring long-term reliability in harsh environments. Disadvantages include lower component density, larger board size, and higher labor or equipment costs for high-volume production compared with SMT. As a result, through-hole remains common in aerospace, military, automotive, and other high-reliability or prototyping contexts, while SMT dominates consumer electronics and high-volume manufacturing.