Fiducials
(Global and Local)
The top camera of placement vision systems scans the surface of the board to locate
fiducials. The fiducials serve as targets used by the placement system to offset
the coordinates in the computer for any variation in true board location. Logas
recommends that ‘local’ and ‘universal’ fiducials be added to PCB’s.
There is also an option to ignore
this step during component mounting, but that
will cause the placement system to assume that the PCB, while clamped or held firm
for placement, is in the accurate position.
The option of ignoring the fiducial check before placement
is not ideal for PCB’s with fine pitch components, BGA’s etc. or heavily populated
boards. ‘Scattered’ fiducials could be local to individual parts as well as group
of parts in a region. Figure 5 illustrates the fiducial requirements.
Fig 4: Fiducials |