IEC TR 61188-8-2021 pdf Circuit boards and circuit board assemblies – Design and use – Part 8: 3D shape data for CAD component library

5.6 Reference point and placement angle Rules for 2D drawings 5.6.1 The rules for 2D drawings are as follows: a) components and land patterns are drawn in top view; b) the component point of origin is shown by “+” or “x”; c) A circumscribing rectangle which contains the component body and land patterns (in top view) should be a part of the library component description. This rectangle is the “Courtyard” that provides a minimum electrical and physical clearance for the part and the land pattern. The point of origin of the description should match that of the component and land pattern. The descriptions of the components, land patterns, and circumscribed rectangles, described are the same in the computer library, and each description uses the same origin coordinates. It is recommended that the point of origin is the same as the way the component is positioned on the final design of the board which is normally by the centroid of the component body. 5.6.2 Rules for 3D shape models (component with no moving part) The rules for 3D shape models (component with no moving part) described are as follows: a) relation between 2D drawing and 3D shape model; It is desirable to design the reference point and placement angle according to the same rules. b) reference point; The center of the outline of the largest rectangle containing the electrodes described are the reference point. The sitting plane is considered to have a Z value of 0, and the direction moving below the seating plane is considered the minus direction of the Z-axis. c) placement angle Indicate the polarity so that it is in the minus direction in the X-axis or in the minus directions of both X- and Y-axes. The example of placement angle is shown in Figure 2.