The through hole mounting refers to a process where the component leads are inserted into the drilled holes on a bare PCB. This process was deemed a standard until a new process came into being in the 1980s, the surface mount technology or SMT. Although there was a drop in its popularity, the through hole technology was still resilient when SMT was the new and popular process. It also bore many advantages and niche applications like reliability. The components of through hole mounting are utilized for high reliability products that may need a stronger and stable connections amid the layers. SMT components can only be secured by solder on the board surface, and through hole components run through the board letting the parts to tolerate more stress.
Hence, military and aerospace always uses through hole because such environments always go through, extreme collisions, accelerations and high temperatures. This technology also comes in handy in testing and prototyping applications that need manual adjustments and replacements. When using through hole technology, always consider the cost and availability.
Types of through hole components
Through hole components have two types: axial and radial lead components. The former runs through a component in a straight line, or in other words, axially where each end of the lead wire exits the component from any of the ends. Both ends are then kept through the separate holes in the board, letting the component to fit closer and flatly.
On the other hand, radial lead components tend to protrude from the board because the leads are equipped on the other side of the component. Both the component types are referred to as twin lead components and have their own set of advantages. The axial lead components are utilized for their snugness nature to the board and the radial leads take less surface area, rendering them ideal for high density boards. Usually, axial lead configurations are available as carbon resistors, fuses, electrolytic capacitors, and light emitting diodes or LEDs. And the radial lead components provide ceramic disk capacitors.
Pros: THM has stronger mechanical bonds as compared to SMT, which is ideal in the case of mechanical stress like transformers and conductors. Ideal for testing and prototyping.
Disadvantages: THM needs drilling holes which is time and money consuming. It also restricts the available routing area on any kind of multilayer board as the drilled holes must pass via all the layers of PCB.