In through hole technology, the components are mounted on the PCB board by inserting their leads through the respective hole. These holes are called through holes since they are drilled from the top to the bottom of the board.

Non-Plated/ Unplated Through Holes or NPTHs have no copper plating on the inner walls and thus provide no electrical properties. Such holes were implemented in single-sided Flex rigid PCB, but their use decreased when multi-layer PCBs became a reality. The only advantage of NPTHs is that it is a simple and cost-effective manufacturing process with quick implementation. Nowadays, they are frequently used as tooling holes to fix the Flex rigid PCB to its operational location. An unplated hole is used for mounting hardware that is not intended to make connections to any of the circuits on the PCB.