Fiducial Mark
The external dimensions of printed circuit boards frequently are subject to large tolerances. To program a pick-and-place system to populate boards with fine pitch components, or to align the printing stencil to the pads on the board during the printing process, these tolerances are frequently way too large. Therefore, to be able to set up these automatic systems to be aligned with the conductive pattern of the board, fiducial marks are placed on the board, together with the conductive pattern. In this way, the fiducials have always the same position in relation to the pads on the board. With the help of camera systems, it is now possible to align these fiducial marks on the board to the placement heads of the pick-and-place unit or to the stencil of the printer. The tolerances of the external board dimension are now being compensated for.