The use of sophisticated component placement machines in manufacturing printed circuit or similar cards, boards, panels, etc. is well known. The term printed circuit board (PCB) as used herein refers to any such electronic packaging structure. Typically, reels of tape-mounted circuit components are supplied to the placement machine by multiple feeders, each of which holds a reel of components. A pick station by each feeder assembly provides components. A rotatable frame is equipped with multiple pick/place heads, each having an extendable vacuum spindle that may be moved in the Z-axis (i.e., in and out) between and extended and a retracted position. The rotatable frame itself is mounted in a housing that may be moved along both the X and Y axes in a plane above a PCB being populated. Each vacuum spindle is equipped with a vacuum nozzle at its tip. The vacuum nozzles are sized and otherwise configured for use with each different size and style of component to be placed by the machine.
In operation, the housing with the rotatable frame holding the pick/place heads is moved to the pick station and the vacuum nozzle is positioned over a tape-mounted component. The vacuum spindle is lowered (i.e., extended) to a point where, upon application of vacuum, the component is removed from its backing tape, centered, and held tightly against the vacuum nozzle orifice. The rotatable frame is then moved to a point over the printed circuit board being assembled, the vacuum spindle is lowered, and the component is deposited on the printed circuit board at a predetermined location.
As component sizes have shrunk, the accuracy of placement of the vacuum nozzle over the component being picked has become more critical. Typically, calibration routines are performed upon machine setup or periodically as required for operation of the machine. However, with micro-miniature components, small variations occurring over time can quickly lead to miss-picks, as well as recognition and orientation problems of these components.
Currently, component placement assembly machines utilize multi-head frames to improve assembly speed. Each frame contains multiple pick/place heads with vacuum spindles, each vacuum spindle having its own vacuum nozzle. With multi-head machines, the need for real-time monitoring of the vacuum nozzle positions becomes even more critical. A vacuum nozzle's position may vary over time due to mechanical binding, build-up of debris, damage to the vacuum nozzle, thermal drift, etc. A changed vacuum nozzle position can be difficult to determine, manifesting its presence only through intermittent pick problems from the various feeders being used to supply the components for placement on the printed circuit boards and through component recognition and orientation errors. If the component itself is misaligned on the PCB, such an error can obviously affect proper operation of other components and larger assemblies.