PCB NC Drill File Format

To assemble the PCB at Newmatik and to have the bare PCB manufactured at one of our suppliers, we need proper Gerber Files and Drill Files. This article aims at explaining the problem with non-standardized drill files and explains the required data format.

The Problem

CAD software exports often create NC ("numeric control") files that do not conform to any standardized specification. These files often contain a few IPC-NC-349 commands, but follow neither the Excellon nor the IPC-NC-349 specification. Commands are not used properly, or are used in a syntactically incorrect way. Usually, the header is incomplete: the scale or the tool diameters are missing. Sometimes there is no header at all, and the file only contains tool numbers, with an unspecified diameter, and X, Y coordinates, in an unspecified unit. They are often called Excellon files, although they really are undefined NC files.

Receiving non-standardized NC Drill Files means that there is a manual process of data preparation before files are ready for import and usage. This is an avoidable source of error.

Providing XNC (IPC-NC-349) Drill Files

The solution to the problem is providing NC Drill Files in the XNC format.

The XNC format is a strict subset of the IPC-NC-349 specification targeted at data exchange between the PCB designer and the PCB manufacturer. The IPC-NC-349 format is the only IPC standard governing drill and routing formats.

The name XNC format stands for EXchange NC format. As a strict subset, it is highly compatible with existing software. Its purpose is to address the current chaos of different subsets and incomplete NC files, and define a simple common standard. The XNC subset was defined by a consortium formed by Graphicode, Ucamco, KiCad and Pentalogix.

The specification is freely available among others at the Ucamco download page. The specification is brief, detailed, easy to understand and unambiguous.

Dowloads:

• XNC Format Specification - Revision 2021.11 (pdf)
• XNC Format Feature Article (pdf)

Example of a XNC Drill File:

M48                 Start of header
METRIC              Metric units (mm)
T01C0.6             Tool 1 has diameter 0.6mm
T02C1.0             Tool 2 has diameter 1.0mm
%                   End of header
G05                 Set drill mode
T01                 Select tool 1
X8.5Y4.8            Drill a hole of 0.6 mm at coordinates 8.5mm,4.8mm
X8.55Y2.85          Drill
X6.54Y2.85          Drill
X6.45Y4.8           Drill
T02                 Select tool 2
G00X10.25Y3.825     Move to coordinates 10.25mm,3.825mm
M15                 Plunge rout tool down
G01X6.50Y3.25       Rout to coordinates 6.5mm,3.25mm
M16                 Lift rout tool up
M30                 End of file