Definition

The Excellon format is a format used to drive CNC drilling and routing machines in electronics manufacturing

Electronics manufacturing

The industrial electronics manufacturing process for the electronic assemblies found in many of today's electronic devices, is a multi-step process.-Component and PCB manufacturing:...

 of printed circuit board

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

s (PCBs). It is a variant of the EIA RS-274-C standard.

It is an ASCII format consisting of commands to drill holes of specific diameters at specific locations on a PCB. A sample file:

M48
METRIC,TZ
FMAT,2
ICI,OFF
T02C0.8000
T01C0.9000
T03C1.9500
T04C3.2000
%
M71
G90
G93X0Y0
T02
X125730Y16193
Y16828
Y17463
...
M30

The name Excellon format is derived from the Excellon Automation Company, which was market leader in PCB drilling and routing

Routing

Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...

 machines during the 1980's, and whose NC format became widely used.

The IPC

IPC

IPC may refer to:*International Poverty Centre, of the United Nations Development Programme*IPC International, a shopping center security company*Ikano Power Centre, a shopping mall in Mutiara Damansara, Selangor, Malaysia...

 organization defined a standard for NC files, the IPC-NC-349 format, which is similar to the Excellon format.

Usage

The Excellon format is used to exchange drill and rout data between CAD/CAM systems as well as to drive CNC machines. The Excellon format was designed for and is suited for driving a NC drilling machine. (There as some issues about specifying the coordinate format though.) It is not ideal for exchanging data between CAD/CAM systems: essential information such as plating and drill span is missing.

For data exchange between CAD/CAM systems it is more practical to describe the drill data in Gerber RS-274X format. This is also a simple format, and quality of the RS-274X software is usually better than that of the Excellon output processors.

Excellon-like files

The name Excellon format or Excellon file is also commonly used for files that only vaguely follow any specification. These files contain a few Excellon commands, but follow neither the Excellon nor the IPC-NC-349 specification. It would be more appropriate to call them Excellon like or generic NC files. Commands are not used properly. Syntactically incorrect commands are thrown in, or even binary junk. Sometimes the historic EIA or EBCDIC character encoding is used instead of ASCII as required by the standards. Usually the header is incomplete: essential information such as the scale or the tool diameters is 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. An example:

%
T01
X006272Y001092
X006354Y001093
X006653Y001092
...
T02
X008091Y001754
X-002028
M30

These files are meaningless without additional information, typically put in a free format human readable tool file. This information must be re-entered manually by the CAD/CAM operator. When critical information is missing (e.g. ommiting leading or trailing zeroes without properly documenting if and which zeroes are omitted) the file is ambiguous. The user may substitute his own judgement or stop the job pending clarification.

These inadequate Excellon-like files are often used. They result in unnecessary manual labor and possibility of delays or errors. These so-called Excellon files give the format a worse reputation than it deserves.

External links

• Official Excellon format description (archived from the original on 2007-10-30)
• IPC