Do Pick and Place machines check their work?
The machine will detect failure to pick a part up to the point where the vision system sees it, but not usually afterwards.
The normal process is for PCBs to be visually inspected, either manually or automatically as a seperate process after placement, to detect misplaced or dropped parts.
Most P&amp;Ps will probably not know they have dropped a part after it has been imaged, although it is possible some might sense placement pressure and/or vacuum pressure to detect drops, however if set up properly, drops shouldn't really happen.