Through Hole Plating
Through holes on a PCB refer to a hole that is drilled from the top and through to the bottom of a PCB, these can be plated (PTH) or non-plated (NPTH).
Through-hole technology, also spelled “thru-hole”, refers to the mounting scheme used for electronic components that involves the use of leads on the components that are inserted into holes drilled in PCBs and soldered to pads on the opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines.
Through-hole technology almost completely replaced earlier electronics assembly techniques such as wire wrapping. From the second generation of computers in the 1950s until surface-mount-technology (SMT) became popular in the late 1980s, every component on a typical PCB was a through-hole component.
PCBs initially had tracks printed on one side only, later both sides, then multi-layer boards were in use. Through holes became plated-through holes (PTH) for the components to contact the required conductive layers. Plated-through holes are no longer required with SMT boards for making the component connections but are still used for making interconnections between the layers and in this role are more usually called vias.
NOTE: Code Red Tronics is currently researching on Through Hole Plating as the number one priority because this will boost the quality of double layer PCBs to a next level.