Noncontact Bent Pin Detection Using Laser Diffraction

The use of optical diffraction is investigated to detect bent pins on a high-density multi-chip integrated-circuit module as an intermediate step in a robotic assembly process. A fixed laser beam shines on a fixed optical array while the robot moves the pins of the module through the beam at four different orientations. (While two scans are mathematically adequate, four scans are required because of the physical characteristics of this particular module.) The optical array is continuously scanned and the resultant images are processed to detect specific abnormalities in the diffraction pattern. If a flaw is detected, software determines the approximate location of the defective pin and whether it should be straightened manually or sent back for rework (determined by the angle of bend).