Through Hole technology is a method for constructing electronic circuits in which the pin-through hole (PTH) components are inserted through holes drilled into printed circuit boards (PCBs). The ends, or leads, are then affixed to pads on the opposite side with molten metal solder using wave soldering or re-flow soldering equipment. This process is also called through hole assembly.
Through Hole technology replaced early electronics assembly techniques such as point-to-point construction. From the second generation of computers in the 1950s until surface-mount technology became popular in the late 1980s, every component on a typical PCB was a through hole component.
Through Hole Technology Process Steps
Component placement: For THT, the component leads or pins are inserted through the board.
Inspection and correction: Any errors in placement will be corrected here.
Wave soldering: For wave soldering, one side of the entire board is exposed to a “wave” of solder. As the board traverses the wave, the through-hole components are soldered simultaneously.
Through Hole Technology (THT) Pros and Cons
The bonds created between THT components and the board is far stronger than SMT bonds. This makes THT the ideal choice for components that will undergo mechanical and environmental stress or high heat, such as transformers.
THT components are also easy to swap out, making them perfect for prototypes and testing.
In THT the PCBs must be pre-drilled, which is both expensive and time-consuming. It also restricts components to one side of the board and limits the available routing area on multi-layer boards since the holes must be drilled through all the PCB’s layers.
THT’s soldering process often makes the resulting solder points less reliable than SMT solder.
THT assembly process is more expensive than SMT.
Through Hole Technology versus Surface Mount Technology Process – How to choose?
For complex boards SMT is regarded as a better option as the THT process takes longer and is more expensive. For large components, such as transformers and high power industrial PCBs that may be subject to high temperatures, stresses and vibrations, THT is usually the better choice. In most cases, the choice is not easy to make and blending both processes to gain the benefits of each is the best way out. Combining both processes during assembly, can give the strength and reliability of THT while preserving the overall cost and efficiency benefits of SMT.