Evaluation of drilled circuit boards using scanning white light interference microscopy

Abstract

The evaluation of drilled circuit board holes has traditionally involved examining the cross-section of a hole using an optical or scanning electron microscope. The objective of this thesis was to compare the use of a Scanning Electron Microscope (SEM) and a Scanning White Light Interference Microscope (SWLIM) for use in drilled circuit board hole inspection. The thesis had two experiments to complete the objective. The first experiment evaluated drilled holes using both a scanning electron microscope and a scanning white light interference microscope (SWLIM) in order to-directly compare the two methods. The second experiment related the quantitative surface texture measurements given by the SWLIM to the drilling factors speed, chip load, number of panels in a stack. number of hits and head height (indicative of time between drilling holes). ,Experiment I addressed the first objective and showed that the SEM is an excellent instrument for initially locating defects in drilled circuit board holes, but falls short in providing quantitative depth measurements of the defects. The SWLIM provides more quantitative data on defects, but can require more work to initially identify defects. Experiment 2 statistically related surface texture measurements to drilling parameters using analysis of variance techniques. The experiment showed that chip load, number of panels, and number of hits were significant factors for the arithmetic mean value (R,) and the root-mean-square average (Rq). Speed, number of panels, and number of hits were significant for peak-to-valley roughness (R). Overall, the scanning white light interference microscope was found to be superior to the SEM in providing quantitative measurements of a drilled hole's surface. The experiments showed that the SWLIM is a viable inspection tool for drilled circuit board holes.