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Proceedings Paper

Structured Light Technique Applied To Solder Paste Height Measurement
Author(s): Catherine A. Keely; Charles C. Morehouse
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Paper Abstract

The technique of structured light has been used to measure the height of solder paste "bumps" on surface mount printed wiring boards. The issue of solder paste height and volume is important in the characterization of the surface mount production process, because solder paste shape and volume (among other things) can have a large effect on the final solder joint quality. Inspection of solder paste takes place after the paste is screened or stenciled on the board, and before components are placed. The structured light system was developed as an off-line process monitoring or process development station. The paper discusses some of the technical challenges overcome in the lighting and imaging side of this application. The challenges include applying the system to boards of various colors and translucencies, imaging the laser stripe reflected off different kinds of solder mask, dealing with large variations of reflectance within the same image, and finally analyzing the image in such a way as to obtain very accurate height measurements. In addition, a method for automating the image analysis was incorporated to significantly improve the usability of the system. Parameters investigated while developing the system include the laser color, polarization of the beam, configuration of the structured light components, and laser speckle effects. The accuracy and repeatability of the system was quantified by a study of the errors contributing to the final measurement.

Paper Details

Date Published: 12 March 1988
PDF: 5 pages
Proc. SPIE 0850, Optics, Illumination, and Image Sensing for Machine Vision II, (12 March 1988); doi: 10.1117/12.942863
Show Author Affiliations
Catherine A. Keely, Hewlett Packard (United States)
Charles C. Morehouse, Hewlett Packard (United States)

Published in SPIE Proceedings Vol. 0850:
Optics, Illumination, and Image Sensing for Machine Vision II
Donald J. Svetkoff, Editor(s)

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