PCB Hole Drilling

 
 

There are 3 types of holes in a PCB, Plated Through Hole (PTH), Non-Plated Through Hole (NPTH) and Via Holes, these should not be confused with Slots or Cut-outs.


Keep in mind that PCB fabs don’t have unlimited drill bits to choose from so they will typically convert your drills into millimeters and then round to the nearest 0.05mm. For example: 

  • Drill size of 31mil is converted to 0.7874mm and then rounded to 0.80mm.

  • Drill size of 33mil is converted to 0.8382mm and then rounded to 0.85mm.


It is helpful for the fab if you could separate the drill files into plated (PTH) and non-plated (NPTH) or else they have to guess what you want. Below is how PCBs make decisions on PTH and NPTH when no distinction is given: 

  • For 1-layer boards, all holes are considered as NPTH

  • For 2-layer and multilayer boards, the NPTH are 

    • Non-connected holes without copper pads.

    • Non-connected holes where the copper pad size is equal to or smaller than the  drill size.

    • Connected holes with a copper pad on 1 side (outer) but no connection on any other layer (outer or inner) and no copper pad on the other side.

    • All other holes are plated

  • Typically all via holes are plated through holes. Vias are defined by any hole that is less than or equal to 0.45mm (18mil) in diameter. 


Any drilled holes that overlap the board contour will be handled as detailed below.

  • PTH holes with copper pads that overhang the board edge will be treated as castellated holes and should be clearly indicated in the mechanical layer.

  • NPTH holes without copper pads will be treated as part of the board outline.


Do not overlap drill holes as this may cause drill bits to break and may result in small pieces of material remaining in the hole or voids in the plated hole. The minimum drill hole to drill hole distance is 0.25mm (10mil), this is measured edge to edge of the drill.

Do not use overlapping drills to define slots. Use the mechanical layer to define slots or plated slots and include text to describe what you’re trying to accomplish.