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6 December 2005 Shape measurement of solder bumps by shape-from-focus using varifocal mirror
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Proceedings Volume 6049, Optomechatronic Sensors and Instrumentation; 60490E (2005)
Event: Optomechatronic Technologies 2005, 2005, Sapporo, Japan
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.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Akira Ishii and Jun Mitsudo "Shape measurement of solder bumps by shape-from-focus using varifocal mirror", Proc. SPIE 6049, Optomechatronic Sensors and Instrumentation, 60490E (6 December 2005);


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