TABLE OF CONTENTS The surface properties of interest, surface roughness and camber, are highly dependent on the particle size and method of processing. Surface roughness is a measure of the surface microstructure, and camber is a measure of the devi- ation from flatness. In general, the smaller the particle size, the smoother the surface.
Surface roughness may be measured by electrical or optical means. Electrically, surface roughness is measured by moving a fine-tipped stylus across the surface. The stylus may be attached to a piezoelectric crystal or to a small magnet that moves inside a coil, inducing a voltage that is proportional to the magnitude of the substrate variations. The stylus must have a resolution of 25.4 nm (1 in) to read accurately in the most common ranges. Optically, a coherent light beam from a laser diode or other source is directed onto the surface. The deviations in the substrate surface create interference patterns that are used to calculate the roughness. Optical profilometers have a higher resolution than the electrical versions and are used primarily for very smooth surfaces. For ordinary use, the electrical profilometer is adequate and is widely used to characterize substrates in both manufacturing and laboratory environments.
Camber and waviness are similar in form in that they are variations in flatness over the substrate surface. Referring to Fig. 8.5, camber can be considered to be an overall warpage of the substrate, whereas waviness is more periodic in nature. Both of these factors may occur as...
