The centroid data (“parts centroid” or “component placement”) file is a location map of the components and therefore contains all information regarding the position and orientation of every surface mount component on the circuit board. It is in ASCII text format and consists of X location and Y location, the reference designator, rotation and side of PCB top or bottom. This file is required to place a component on the circuit board. This set of data enables us to properly plan and prepare for the production of your circuits.
The basic format for the Centroid file with data should be in the following order (sample here):
The XY location information is in mil, inch or mm and it is calculated from a given board origin. The rotation is in degrees 0, 45, 90, etc. The layer side is usually defaulted to the top side, but can be expressed as top/bottom (or 0/1 is used by some CAD systems). The XY information should signify the center of the component, as this detail is used by pick-n-place machine to place the components.