Файлы NC для печатных плат: Форматы, стандарты и проблемы обмена данными.

PCB NC drill files convey PCB drilling and routing information. The NC formats were originally designed by CNC drill and route machine vendors as proprietary input formats for their equipment, and are known under their company name: Excellon, Hitachi, Sieb & Meyer, Posalux, etc. These formats are similar as they are based on RS 274 C and related to G code. In 1985 IPC published a generic standard NC format, IPC NC 349. Later XNC was designed, a simple strict subset of IPC NC 349, designed not for driving machines but for exchanging drill information between CAD and CAM. They are collectively referred to as (PCB) NC files. The NC files are primarily used to drive CNC machines, and they are adequate for that task. They are also used to exchange design information between CAD and CAM, for which they are not adequate: essential information such as plating and drill span is missing. Furthermore, the NC output in CAD systems is often poorly implemented, resulting in poor registration between drill holes and copper layers and other problems. To exchange data between CAD and CAM it is more preferred to use the Gerber format. The quality of the Gerber file output software is typically good, and Gerber supports attributes to transfer meta information such as plating and span.

The name Excellon format is derived from the company Excellon Automation (not to be confused with Excellon Software), which was the market leader in PCB drilling and routing machines during the 1980s, and whose proprietary format became widely used. There are actually two Excellon formats, the older Excellon 1 and Excellon 2. Excellon 2 is a superset of IPC NC 349. Commands from both are sometimes confusingly mixed in the same file. Excellon Automation stopped publishing the specification of its format, without statement on the IP and usage rights of the format. An archived copy exists. The specification is ambiguous, leading to different interpretations, especially in the area of coordinates and units. It is targeted at input for drill/rout machines, not CAD to CAM data exchange.