Shape measurement of solder bumps by shape-from-focus using varifocal mirror

Akira Ishii; Jun Mitsudo

doi:10.1117/12.648791

6 December 2005 Shape measurement of solder bumps by shape-from-focus using varifocal mirror

Akira Ishii, Jun Mitsudo

Proceedings Volume 6049, Optomechatronic Sensors and Instrumentation; 60490E (2005) https://doi.org/10.1117/12.648791
Event: Optomechatronic Technologies 2005, 2005, Sapporo, Japan

Abstract

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.

Citation Download Citation

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); https://doi.org/10.1117/12.648791

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