This paper describes a real-time system for measuring the three-dimensional shape of solder bumps arrayed on an LSI
chip-size-package (CSP) board presented for inspection based on the shape-from-focus technique. It uses a copper-alloy
mirror deformed by a piezoelectric actuator as a varifocal mirror enabling a simple, fast, precise focusing mechanism
without moving parts to be built. A practical measuring speed of 1.69 s/package for a small CSP board (4 x 4 mm2) was
achieved by incorporating an exclusive field programmable gate array processor to calculate focus measure and by
constructing a domed array of LEDs as a high-intensity, uniform illumination system so that a fast (150 fps) and
high-resolution (1024 x 1024 pixels/frame) CMOS image sensor could be used. Accurate measurements of bump height
were also achieved with errors of 10 μm (2σ) meeting the requirements for testing the coplanarity of a bump array.
We devised a new method of shape-from-focus to model a robotic work space. The focused-plane in the new method of focused-plane sectioning was rotated around the axis located at the front focal point of an imaging lens to be able to scan omni-directionally and obtain panoramic range data on the space where objects were located. The astigmatism of the image-taking lens was a major factor causing systematic errors in detecting the 3-D coordinates of the objects. The measurement errors depended on the direction of the object contours. We devised an effective method of correction, where the coordinates of a contour point were corrected by detecting the edge direction of a contour image and interpolating the line-of-sight range and azimuthal angle of the contour point between the predetermined ranges and azimuthal angles of the horizontal and vertical contour points using the direction of the measured contour. After correction, the lateral position errors were less than 0.17 mm and the range errors were less than 8.6 mm on the contour in a direction of 45° at a distance of 730 mm.
This paper describes a method of measuring the shape of solder bumps arrayed on an LSI package board presented for inspection based on the shape-from-focus technique. We used a copper-alloy mirror deformed by a piezoelectric actuator as a varifocal mirror to build a simple yet fast focusing-mechanism. The varifocal mirror was situated at the focal point of the image-taking lens in image space so that lateral magnification was constant during focusing and orthographic projection was perfectly established. A focused plane could be shifted along the optical axis with a precision of 1.4 μm in a depth range of 1.5 mm by driving the varifocal mirror. A magnification of 1.97 was maintained during focusing. Evaluating the curvature of field and removing its effect from the depth data reduced errors. The shape of 208 solder bumps 260-μm high arrayed at a pitch of 500 μm on the board was measured. The entire 10 mm x 10 mm board was segmented into 3 x 4 partly overlapping sections. We captured 101 images in each section with a high-resolution camera at different focal points at 15-μm intervals. The shape of almost the entire upper-hemisphere of a solder bump could be measured. Errors in measuring the bump heights were less than 12 μm.
This paper presents a practical shape-from-focus method for measuring three-dimensional shapes on production lines. A focused plane was inclined typically at 45° to an optical axis in an afocal optical system and was imaged on a CCD image sensor, which was also inclined at an angle of 45° to the optical axis. When the focused plane and surface of an object intersect, a contour of the object is defined at each position of the carrier conveying the object. Each contour can be obtained by detecting focused points in an image of the focused plane using a specific focus-measure. To correctly detect the focused points on the right focused-plane image, a sequence of focused-plane images was taken at each position of the carrier moving perpendicular to the optical axis. A focused image point representing a contour point was detected as a specific pixel in a focused-plane image that gave a maximum of focus-measure for the contour point from the focused-plane images taken contiguously while sweeping the object by the focused-plane. Both the detected pixel coordinates and the carrier position producing the focused-plane image, including the detected pixel, could determine the three-dimensional coordinates of the contour point. A minute hemisphere with a diameter of 4.8 mm could be measured with a standard deviation of 16 μm.
An imaging system with a focusing mechanism based on perfect projection was devised using a varifocal mirror to achieve high-quality three-dimensional imaging and precise measurement of shape. We treated two types of projection that were used as an analytical model for machine vision. First, an imaging system based on perspective projection was constructed so that the varifocal mirror was placed at the front focal point of the image taking lens. Magnification was exactly equal to the ratio of the focal length and an object point distance from the front focal point of the lens, which was fixed when focusing with the varifocal mirror. The surface shape of a spherical dent (3.5 mm in diameter) was precisely measured with the shape-from-focus-method because the dent could be viewed from the side. Second, we constructed an imaging system with a focus mechanism based on orthographic projection so that the varifocal mirror could be placed at the back focal point. The system was able to be focused on any object point at constant magnification. Taking advantage of parallel projection, an entirely focused 3-D image of a screw thread (2 mm in diameter) and its profile could successfully be obtained using the shape-from-focus method.
This paper describes a technique, based on the shape-from-focus method, to measure the shapes and heights of an array of solder bumps through visually inspecting an IC chip-size package (CSP). We devised a focus measure difference method for detecting the horizontal section of a bump quickly and precisely. This was where we selected bump image pixels that had the same focus measure at two specified focal points along the height axis. The selected pixels corresponded to the contour points of the section at the mid-height between the two focal points. We applied it to measuring the height of an array of 208 bumps that were 260 μm high arranged at intervals of 500 μm. By measuring the area of the horizontal section at a specified height and using it to fit a sphere in the bump, the height of the bump top was efficiently estimated to match the sphere top. This sphere fitting achieved a height measurement accuracy of 8 μm (2σ) at a resolution of 3.4 μm pixels on the bump using a 2/3-inch high resolution CCD camera with 1300 × 1030 pixels. The accuracy was sufficient to inspect the coplanarity of an array of solder bumps.
This paper describes optical tomography using oblique and confocal fan-beam illumination devised for transparent-layered objects. This 3-D imaging method has the advantage of area-at-a-time sensing and it is free from disturbances caused by defects on the object surface, compared with the conventional confocal microscopy based on point-by-point sensing and co-axial illumination. The method was applied to LCD panel inspection and was successful in efficiently detecting foreign substances between the constituent layers in LCD. Furthermore, it was robust against scratches and dust on the protection film surface of the LCD.
This paper describes a varifocal system having constant magnification that consists of a telecentric lens and a varifocal spherical mirror. The feasibility of using this system was made clear through a computational evaluation of the imaging characteristics and by experiments. The evaluated resolution and TV distortion were 100 lp/mm and 0.04 percent at a magnification of 2 in a visual field of 3.3 mm × 4.4 mm, respectively. Basic experiments using concave-mirrors having different curvature-radii showed similar results. A focal shift of 3.42 mm was obtained with a concave mirror having a 600-mm curvature radius without a change of magnification. Further, a prototype system using a pneumatically controlled varifocal mirror successfully demonstrated constant-magnification focusing. The varifocal mirror was a circular 320-μm-thick glass plate, the optical aperture of which was 6 mm in diameter. Its curvature was controlled pneumatically to shift the focal point of the varifocal system. The focal shift reached 1.1 mm without image impairment occurring. Focus measure analysis produced a 3-D focused image of a screw thread 2 mm in diameter from 50 images taken at 20-μm depth intervals, and a contour map of the screw thread is also presented.
We have developed a full-color inspection system that detects defects such as pin-holes and stains on surface of prepaid cards. The system consists ofa card conveyer unit with an automatic exchange mechanism and a custom designed image processing unit with a three-stage pipeline structure. Inspection performance ofO. 7 seconds/card with a defect detection resolution of 0. 1 5mm diameter is achieved with a new algorithm that reflects human visual criteria.
This paper presents a flexible and highly-reliable gray-level vision system based on multiple cell-feature descriptions using only three basic operation modules: extended convolution radially traversing probing and histogram compression. The generalized Hough transform is introduced as a universal method for object model matching. Model learning is automatically performed by acquiring image samples while rotating each object. A prototype system demonstrates successful recognition of mechanical parts.
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