Profile measurement for printed wiring boards

Abstract

We developed pattern inspection techniques for simultaneously measuring both the width and the thickness of conductive patterns printed on ceramic green sheets. The measuring optics use a He-Ne laser scanner. Thickness is measured by beam splitting, and width, by light diffusion. The beam-splitting optics measure the height by determining the ratio of reflected to transmitted light intensity. By optimizing the arrangement of the optics, we attain a resolution of 5 im and a height measurement range of [70 pm. Pattern width measurement is based on the fact that a beam of light diffuses when it strikes the substrate, but does not diffuse when it strikes the conductive pattern. A spatial ifiter in the focal plane raises the S/N ratio to four regardless of the state of the conductor surface. We used these techniques to inspect the conductive patterns on green sheets. Our system inspects conductor patterns 3-dimensionally at 12 Mplxels per second with a 5 i.m resolution.