Placing Surface Mount Components Using Coarse/Fine Positioning and Vision

Abstract

Fine pitch surface mount devices (SMD’s) are becoming more frequently used in circuit board manufacturing. These components have many closely spaced leads that are soldered to pads on a printed circuit board (PCB). Better accuracy in aligning the device to the PCB pads is needed as the number of external device leads increase and the pitch between the leads becomes smaller. This paper describes an experimental system that can accurately align and place SMD’s on a PCB, using a coarse/fine positioning component placement strategy and end point sensing to measure the alignment error. Coarse positioning is done with an IBM 7576 robot and fine positioning using a custom designed precision micropositioning device attached to the end of the IBM 7576 robot. The endpoint sensor is a single camera vision system that by image analysis determines the alignment error of the SMD to the board. System performance was evaluated by placing SMD’s of 100 leads with 0.63-mm (25 mil) lead spacing on a board. An alignment error of less than 12 μm (0.5 mil) and 0.015° was obtained independent of feeder and board position error or robot repeatability. The average cycle time is less than 10 s. © 1990 IEEE