Paper:
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
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.
- [1] G. Bickel, G. Hausler, and M. Maul, “Triangulation with expanded range of depth,” Optical Engineering, 24, 6, pp. 975-977, 1985.
- [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] M. Schonleber and H. J. Tiziani, “Fast and flexible shape control with adaptive LCD fringe masks,” Proc. SPIE, 3098, pp. 35-38, 1997.
- [4] M. Gu, “Principles of Three-Dimensional Imaging in Confocal Microscopes,” World Scientific, pp. 1-13, 1996.
- [5] D. L. Dickensheets and G. S. Kino, “Micromachined scanning confocal optical microscope,” Optics Letters, 21, 10, pp. 764-766, 1996.
- [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] S. K. Nayar and Y. Nakagawa, “Shape from Focus,” IEEE Trans. PAMI, 16, 8, pp. 824-831, 1994.
- [8] Adaptive Optics for CO2 Laser Material Processing, Technical Description, Adaptive Mirror 40 mm Dia., Diehl Stiftung & Co., Systemtechnik Dept., Roethenbach/Pegnitz, Germany, 1999.
This article is published under a Creative Commons Attribution-NoDerivatives 4.0 Internationa License.
Copyright© 2006 by Fuji Technology Press Ltd. and Japan Society of Mechanical Engineers. All right reserved.