doi:10.3850/978-981-08-7723-1_P144

ABSTRACT

A simple method for evaluating the surfaces of through-holes in printed wiring boards is required in engineering applications. We have studied diffraction in the shadow region created by a micron-sized projection on a flat board (such as a thin obstacle). A curved diffraction fringe was clearly observed in the shadow region corresponding to the position of the small projection. This diffraction phenomenon in the shadow region produced by a small projection can be used to examine the surfaces of through-holes in a printed wiring board as well as the surfaces of flat boards. In this paper, we present experimental results for diffraction in the shadow region produced by micron-sized projections on a flat board and the inner surfaces of tubes. The relationship between the fringe spacing and the position of the projection on the sample surface is experimentally determined. The first maximum peak in the interference pattern produced by a small projection illuminated by coherent light can be used to evaluate and measure a small projection on a flat board. We propose applying this interference phenomenon to evaluate and measure the surface of a through-hole using unidirectional illumination.

Keywords: Laser diffraction, 3D, Scratch, Inner surface, Through-hole.

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