Through-hole mounting is one of the two main methods of components on a PCB. And such PCB requires through holes to mount the components. Through hole mounting is also called DIP(dual inline-pin package) or THT(through hole technology). The other major mounting method is Surface Mounting Technology(SMT).

Through-hole mounting involves leads being inserted into holes that have been drilled into the PCB board. With the advent of SMT, it was widely presumed that THM would be phased out. However, manufacturers still make THM PCBs, as there are clients who still prefer, or require boards that use the older board design. The main reason is that THM boards have greater reliability.

The reasons for better reliability are evident. SMT components are secured to the board by solder only. THM components are secured by leads or pins running through the board. The result is that the THM boards can hold up in more stressful environment. As a result, boards used in military or aerospace situations often specify THM boards, as the PCB working conditions may include very high or very low temperatures, or rapid acceleration.

There are other reasons that THM boards continue to be used. A common use of THM boards is in prototype testing, as the board structure allows for manual adjustments. Not all components are available for surface mount situations. And in some instances, THM components are less expensive than the equivalent SMT component.

However, the benefit of lower cost components needs to be balanced with the higher cost of preparing the THM. The THM board needs to have holes drilled, which can be an expensive process, as well as being time consuming.

Another issue with THM boards is layering. Drilled holes must pass through all layers of the PCB. Therefore, routing on multilayer boards is more challenging for THM.

In summary, THM boards have become a specialist product, providing a valuable tool in specific situations such as high temperatures, or situations that may involve mechanical stress.