Shape Measurement of Solder Bumps by Shape-from-Focus Using Varifocal Mirror

Jun Mitsudo; Akira Ishii

doi:10.20965/jrm.2006.p0722

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JRM Vol.18 No.6 pp. 722-727

doi: 10.20965/jrm.2006.p0722

(2006)

Paper:

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Shape Measurement of Solder Bumps by Shape-from-Focus Using Varifocal Mirror

Jun Mitsudo and Akira Ishii

Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu-shi, Shiga 525-8577, Japan

Received:

March 30, 2006

Accepted:

August 28, 2006

Published:

December 20, 2006

Keywords:

visual inspection, shape from focus, LSI package, solder bump, varifocal mirror

Abstract

We measured solder bumps on an LSI package board presented for inspection based on the shape from focus. We used a copper-alloy mirror deformed by a piezoelectric actuator as a varifocal mirror to build a motionless yet fast focusing mechanism. The varifocal mirror was at the image focal point of the image-taking lens so that lateral magnification was constant during focusing and orthographic projection was established. A focused plane was shifted along the optical axis with a precision of 1.4μm in a depth range of 1.5mm 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 spaced 500μm on the board was measured. The 10mm×10mm board was segmented into partly overlapping 3×4 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. Error in measuring bump heights was less than 12μm.

Cite this article as:

J. Mitsudo and A. Ishii, “Shape Measurement of Solder Bumps by Shape-from-Focus Using Varifocal Mirror,” J. Robot. Mechatron., Vol.18, No.6, pp. 722-727, 2006.

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References

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This article is published under a Creative Commons Attribution-NoDerivatives 4.0 Internationa License.

[1] [1] G. Bickel, G. Hausler, and M. Maul, “Triangulation with expanded range of depth,” Optical Engineering, 24, 6, pp. 975-977, 1985.

[2] [2] K. Araki et al., “High speed and continuous 3-D measurement system,” Proc. 11th IAPR Int. Conf. on Pattern Recognition, 4, pp. 62-65, 1992.

[3] [3] M. Schonleber and H. J. Tiziani, “Fast and flexible shape control with adaptive LCD fringe masks,” Proc. SPIE, 3098, pp. 35-38, 1997.

[4] [4] M. Gu, “Principles of Three-Dimensional Imaging in Confocal Microscopes,” World Scientific, pp. 1-13, 1996.

[5] [5] D. L. Dickensheets and G. S. Kino, “Micromachined scanning confocal optical microscope,” Optics Letters, 21, 10, pp. 764-766, 1996.

[6] [6] M. Ishihara and H. Sasaki, “High-speed surface measurement using a nonscanning multiple-beam confocal microscope,” Optical Engineering, 38, 6, pp. 1035-1040, 1999.

[7] [7] S. K. Nayar and Y. Nakagawa, “Shape from Focus,” IEEE Trans. PAMI, 16, 8, pp. 824-831, 1994.

[8] [8] Adaptive Optics for CO₂ Laser Material Processing, Technical Description, Adaptive Mirror 40 mm Dia., Diehl Stiftung & Co., Systemtechnik Dept., Roethenbach/Pegnitz, Germany, 1999.