1 January 1991 System calibration and part alignment for inspection of 2-D electronic circuit patterns
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This paper describes a system calibration and part alignment approach for inspection of 2D electronic circuit pattems. Fast and robust techniques for measuring image features in these procedures are presented. The approach and techniques have been validated on a prototype system implementation consisting of a PC-AT, a stationary microscope with a CCD camera interfaced to a commercial frame grabber board, and a rotation platform mounted on an X-Y stage that transports the part during inspection. System calibration finds the parameters that map pixels into physical units and that map X-Y stage units into physical units. Each mapping is modeled with a 2D affine transformation obtained by least-squares fitting measured image features to physical units. System calibration also determines the axis of the rotation platform accurately and corrects for nonuniformity in pixel sensitivity. Features of a calibration part are detected with robust techniques that reduce the likelihood of spurious detection and hence relax constraints for a completely contamination-free calibration part. Subpixel measurements are conducted in edge profiles of row and column projections of image sections. Edges of opposite polarity and similar magnitude which are sufficiently close to each other are grouped into pairs and considered spurious. Feature detection is conducted at two different image regions to verify authenticity and obtain a more accurate measurement. The axis of the rotation platform is calculated by rotating CW and CCW and measuring corresponding features of the calibration part after each rotation. Measurement of rotation during this step and in the alignment procedure is obtained by mapping a quadrilateral in 2D measurement space onto a rectangle. This compensates for minor global variations in height that the part may exhibit due to placement. It also makes the alignment procedure independent of knowledge of the physical coordinates of the features that defme the vertices of the rectangle. Analytical solutions for the measurement of rotation and the axis of the rotation platform are presented.
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Arturo A. Rodriguez, Arturo A. Rodriguez, Jon R. Mandeville, Jon R. Mandeville, Frederick Y. Wu, Frederick Y. Wu, } "System calibration and part alignment for inspection of 2-D electronic circuit patterns", Proc. SPIE 1332, Optical Testing and Metrology III: Recent Advances in Industrial Optical Inspection, (1 January 1991); doi: 10.1117/12.51084; https://doi.org/10.1117/12.51084

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