Quantitative 3D surface profiling inspection of glass core PCB using nanometer resolution off-axis digital holographic microscopy

Abstract

Accurate 3D surface profiling of glass core printed circuit boards (glass PCBs) is critical for the reliability of advanced electronic packaging. Conventional automated optical inspection methods provide only 2D information without quantifying surface height, while white light interferometry suffers from slow speed and high cost. To address these limitations, this study applies an off-axis digital holographic microscopy (DHM) system to quantitative 3D surface profiling of glass PCBs and systematically evaluates its metrological performance using representative industrial surface features. A quality-guided phase unwrapping algorithm is implemented to accurately reconstruct the surface topography. The system achieves a field of view of approximately 2000 × 2400 μm2 and a height measurement accuracy of 0.02 µm, validated using the USAF 1951 resolution test target. Four representative surface features are measured and quantified: convex-type protrusions (step height ∼ 0.16 μm), concave-type surface pits (depth∼0.18 μm), large area irregular topography (2000 × 2400 μm2), and a spatially extended elevated feature (maximum reconstructed height ∼ 0.27 μm). Comparative measurements conducted using a commercial white-light interferometer reveal excellent agreement with the developed DHM system in both 2D height maps and cross-sectional profiles. The single-shot acquisition capability enables full-field quantitative profiling without mechanical axial scanning, demonstrating the potential of the DHM system for non-contact inspection of glass PCBs.