Jon R. Mandeville

Algorithms for a fast confocal optical inspection system

Confocal imaging is an emerging technique for the measurement of surface topography in inspection. The authors present a system designed for fast acquisition and processing of confocal images, which consists of an optical front end using tilted confocal scanning, and an image processing module. The function of the image processing module is to improve signal resolution, perform smoothing and detect surfaces in the incoming signal. The input signal is first deconvolved in order to improve the depth resolution, and then processed to identify significant peaks. These peaks represent the position of different surfaces in the object being inspected. These peak locations are smoothed using a cluster based smoothing scheme to combat noise. For semi-transparent materials, the authors system is capable of detecting up to two surfaces at a given location. >

Image registration for automated inspection of printed circuit patterns using CAD reference data

An image registration approach for inspection of printed circuit patterns which has been validated on a prototype system is described. Theoffline procedure forms, selects, prioritizes, and sorts registration features from CAD-generated reference data. A feature is selected if it satisfies clearance rules that account for the maximum expecteddiscongruence between captured and reference images. The sorting scheme considers the detection complexity of a feature and its distance away from the center of the expected image, since outer features represent potential global distortions better. Theruntime registration procedure detects features and finds the parameters that transform pixels into reference data coordinates and vice versa. We represent robust feature-measurement techniques that offer accurate subpixel localization and verify feature authenticity. We describe an edge-detection technique based on a novel way of authenticating zero-crossings and a method that disqualifies edges detected on defects of the part under inspection.

Fast confocal image processing for inspection

The measurement of surface topography is an important inspection task as it provides useful information for process and quality control. A candidate technique for such an application is confocal imaging. The advantages of confocal imaging are that it is a noncontact measurement, can be operated at high speed (greater than 10 megapixels/sec) and submicron resolution, and provides height information in multilayered semitransparent materials. In this paper, we present a scheme for the fast processing of confocal images. The scheme consists of measuring the response function of the confocal system and deriving a deconvolution filter based on this response. The input signal is deconvolved in order to improve the depth resolution and then processed to identify significant peaks. These peaks represent the position of different surfaces in the object being inspected. For semitransparent materials, our scheme is capable of detecting up to two surfaces at a given location.

Calibration and alignmenttechniques for automated inspection of printed circuit patterns

Abstract A system calibration and part alignment approach for inspection of printed circuitpatterns is presented. We describe procedures for optical and X-Y stage calibration, for axis of rotation estimation, and for correction of nonuniformity in pixel sensitivity. Features are detected with fast and robust techniques that reduce the likelihood of spurious detection. In addition, calibration feature detection is conducted at two different image regions to verify authenticity. This relaxes constraints for a completely contamination-free calibration part. The axis of rotation is calculated by rotating clockwise and counterclockwise and measuring corresponding calibration features. Measurement of rotation during this step and in the alignment procedure is obtained by mapping a quadrilateral in 2-D measurement space onto a rectangle to compensate for minor global variations in part height. This also makes the alignment procedure independent of knowledge of the physical coordinates of the features that define the rectangles vertices. Analytical solutions for the measurement of rotation and the axis of the rotation are presented. Good results have been obtained in a prototype inspection define the rectangles vertices. Analytical solutions for the measurement of rotation and the system.

System calibration and part alignment for inspection of 2-D electronic circuit patterns

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.

Novel Method For The Analysis Of Printed Circuit Images

To keep pace with the trend towards increased circuit integration, printed circuit patterns are becoming denser and more complex. A variety of automated visual inspection methods to detect circuit defects during manufacturing have been proposed. This paper describes a method that is a synthesis of the reference-comparison and the generic property approaches that exploits their respective strengths and over-comes their respective weaknesses. It is based on the observation that the local geometric and global topological correctness of a printed circuit can be inferred from the correctness of simplified, skeletal versions of the circuit in a test image. These operations can be realized using simple processing elements which are well suited for implementation in hardware.

Rotation measurement techniques for alignment in PCB automated inspection

Part alignment is an essential element of automated inspection of printed circuit boards. The objective of a part alignment procedure is to measure the global rotation of the part under inspection and the location of its center to properly orient and position the part prior to inspection. This paper describes a set of techniques that effectively accomplishes this task. We describe techniques to rapidly detect fiducials and to accurately measure their location. Measurement of rotation is obtained by mapping a quadrilateral in 2-D measurement space onto a rectangle. This solution compensates for minor global variations in part height and provides an analytical equation to measure the rotation of the part that is independent of knowledge of the physical coordinates of the fiducials.

Image registration for automated inspection of 2-D electronic circuit patterns

An image registration approach for inspection of 2D electronic circuit patterns is described. The approach which coisists of an offline procedure and a runhime procedure has been validated on a prototype inspection system. The offline procedure selects and sorts registration features from CAD generated reference data according to a set of prespecified priority selection rules. Preference is given to features expected away from the center of the image since they represent potential distortions better. The size of windows searched during runtime to detect features is ohtamed from the maximum expected system errors and tolerances in part manufacture. To prevent spurious detection during runtime the ofiline procedure selects a feature if no other CAD feature intersects its window The runtime procedure detects edges and measures their image location to suhpixel accuracy within their respective search windows. Edges are detected by authenticating zero-crossings of a second-order differential operator applied to the profile of each search window. Registration is conducted on points composed by averaging the measured location of opposite polarity edges of the same object type and size. This reduces any bias introduced by the edge incasurement technique and prevents offsets that would otherwise be introduced by variations in circuit pattern dimensions. To minimize the likelihood of spurious edge detection (e. g. an edge detected on a defect) the dimension demarcated by the opposite polarity edge pair is monitored. After a significant number registration features have been detected the runtime procedure finds the parameters that transform pixels into CAD reference data coordinates and vice versa. Good results have been obtained in a prototype inspection system.