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) in order for the components to make contact with 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.


  • ≤4.00mm the tolerance on the diameter is +/-0.05mm
  • >4.00mm the tolerance on the diameter is +/-0.10mm


Plated hole

  • Average Cu plating thickness is min 20µm.
  • Any individual hole should have a min of 17µm Cu.
  • Any localised part of a hole wall should have 15µm Cu as a min.
  • The tolerance on the diameter please see Tolerances on a PCB.

Also see our PCB Design Guidelines – Drilled Holes page, our Drilled Holes in the PCB page.

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