Three Dimensional Voxel Scale Calibration Methods for Automated Micro-CT Inspection
Calibrating micro-CT voxel scale with certified ball-bar phantoms bounds geometric magnification drift and ensures repeatable automated void sizing.
Surface Determination
Threshold Extraction
Image segmentation algorithms process three-dimensional volumetric density datasets to locate physical material boundaries between distinct component structures and surrounding air. Performing surface determination establishes discrete CAD-compatible surface meshes from raw grey-scale voxel arrays captured during X-ray computed tomography scans of circuit assemblies. This algorithmic processing determines exact physical dimensions for copper traces, solder joints, and plastic component housings.
The application scope of this segmentation stops at uncalibrated grey-scale datasets where background noise or severe artifact streaks prevent deterministic threshold calculation.
Gradient Calculation
Volumetric grey-scale images generated by CT reconstruction algorithms lack sharp step-function material boundaries due to partial volume effects and focal spot unsharpness. Surface determination employs local grey-scale gradient algorithms, evaluating grey-value derivative peaks along search lines perpendicular to estimated material interfaces. Advanced iterative algorithms adjust surface mesh node coordinates to sub-voxel precision by fitting mathematical profile models to local grey-level intensity gradients.
Accurate boundary placement enables sub-micron dimensional verification of internal microvia geometries, package lead coplanarity, and solder fillet shapes. Computed mesh models undergo direct comparison against nominal CAD models to calculate dimensional deviations across complex assembled boards.
Boundary Accuracy
Material density variations across multi-material assemblies require local adaptive thresholding rather than single global grey-value selection. Artifacts such as beam hardening create false grey-value variations that shift calculated surface locations if left uncorrected. Calibration standards verify threshold accuracy prior to performing critical dimensional inspection routines.