How should fiducials for SMD assembly be optimally designed (size, shape), how many fiducials are necessary, and where should they be placed? Fiducials are absolutely necessary as reference points for paste printing and for automatic SMD placement.
Where are fiducials necessary?
There are three types of fiducials which are standardized in IPC-7351:
Panel Fiducials: On the panel edge, to align the manufacturing panels in the paste printing process. When we procure the PCB, we take care of the optimal panel design and setting of fiducials. If you design the panels by yourself, 3 fiducial marks should be set and the panel should be approved by us.
PCB Fiducials (Global Fiducials): on the individual PCBs for alignment in the pick-and-place machines. PCB fiducials are required on each side assembled with SMD components. 3 fiducials per PCB are optimal and at least 2 are required. Please ensure that the PCB fiducials are also exported in the pick-and-place data.
Local Fiducials: On very large PCBs where high placement precision is required for finepitch IC. This is useful when components have a pitch of less than 0.5 mm.
There must be at least 2 fiducial marks on each PCB (e.g. bottom left and top right). For placement precision and printing precision, 3 fiducial marks each are optimal.
What is the ideal fiducial mark?
A copper dot with a diameter of 1 mm is ideal as a fiducial on the PCB. This must be placed centered in a 2 mm solder mask clearance. This ensures that our camera systems have sufficient contrast to detect the fiducials.
Please ensure that the PCB fiducials are also exported in the pick-and-place data.