Naming Convention for Fiducial Footprints

All 4 types fall into the same category as far as size and shape.

Local Fiducials: Local fiducial marks are used to locate the position of an individual component requiring more precise placement.

For these components, two local fiducial marks are required for correction of translational offsets (x and y position) and rotational offsets (theta position). This can be two marks located diagonally opposed within or outside the perimeter of the land pattern.

All fine pitch components should have two local fiducial systems designed into the component land pattern to insure that enough fiducials are available every time the component is placed, removed and/or replaced on the printed board. All fiducials should have a solder mask opening large enough to keep the optical target absolutely free of solder mask. If solder mask should get onto the optical target, some vision alignment systems may be compromised due to insufficient contrast at the target site.

If space is limited, one may be able to share a fiducial from an adjacent component within the location constraint. Also, if space is limited and the printed board is deemed by manufacturing to be sufficiently small, component fiducials may be omitted and global fiducials used in their place.

Panel and Global Fiducials: Global fiducial marks are used to locate the position of all circuit features on an individual printed board. When a multi-image circuit is processed in panel form, the global fiducials are referred to as panel fiducials.

A minimum of three fiducial marks is required for correction of offsets (x and y position), rotational offsets (theta position) and nonlinear distortions (scaling, stretch and twist). These should be located orthogonally as far apart as possible on the circuit or panel.

It is good design practice to locate global or panel fiducials in a three-point grid-based datum system. The first fiducial is located at the 0-0 location. The second and third fiducials are located in the X and Y directions from 0-0 in the positive quadrant. The global fiducials should be located on the top and bottom layers of all printed boards that contain surface mount as well as through-hole components since even through-hole assembly systems are beginning to utilize vision alignment systems.

Zonal Fiducials: To ensure the accurate placement of multiple surface mount components that are not near ‘component specific local fiducials’ or ‘global fiducials’, additional ‘zonal fiducial targets’ may be placed within a zone or an area of the board assembly to compensate for printed board dimensional stability.