Centroid is the special file for assembly used for quickly programming the assembly machines. This is also known as aka Insertion, Pick-N-Place, or XY Data. Some of the CAD tools will automatically generate this file and some not, but you may need to modify the file and then generate the Centroid file. The Centroid file describes the position and orientation of all the surface mount parts, which includes the reference designator, X and Y position, rotation and side of Board (Top or Bottom). Only surface mounting parts are listed in the Centroid.