Excellon format

The Excellon format is widely used to drive CNC drilling and routing machines in printed circuit board (PCB) manufacturing. It is a variant of the EIA RS-274-C standard.

Below is a sample file:

The name Excellon format is derived from the Excellon Automation Company, which was market leader in PCB drilling and routing machines during the 1980s, and whose proprietary format became widely used.

The IPC organization defined the IPC-NC-349 format as standard NC format. It is similar to the Excellon format.

Usage

The Excellon format was designed for and is primarily used to drive CNC drill and route machines. It is suitable for that task as it can specify machine specific information such drill feed and speed.

The Excellon format is also used to transfer design information from CAD to CAM. It is not adequate for that task: essential information such as plating and drill span is missing. Furthermore, the Excellon output in CAD systems is often poorly implemented, resulting in poor registration between drill holes and copper layers and other problems. For data exchange between CAD/CAM systems it is more practical to describe the drill data in Gerber format as the quality of the Gerber file output software is usually better and Gerber supports attributes to transfer meta-information such as which are the via holes.