Voxellation Artifact
Volumetric reconstruction of X-ray computed tomography images assigns a single gray level value to each three-dimensional pixel voxel based on total X-ray absorption within that discrete volume element. Occurrence of the partial volume effect blurs boundary interfaces where materials of vastly different densities occupy the same individual voxel space. This phenomenon causes thin copper traces or thin solder joint voids to appear with intermediate gray values that match neither copper nor air.
The physical occurrence of this artifact stops when discrete feature boundaries align perfectly with voxel grid coordinates at spatial resolutions significantly finer than the target feature size.
Density Averaging
Spatial sampling limits in digital CT detectors force voxels located along material boundaries to compute an average attenuation value based on the relative volume fractions of adjacent substances. When evaluating microvia plating thickness or thin solder fillets, the partial volume effect reduces apparent peak density while artifically broadening physical feature thickness. Small gas bubbles inside ball grid array solder joints appear larger with lower grey-scale contrast, leading automated defect recognition algorithms to miscalculate total void volume percentages.
Higher geometric magnification and smaller detector pixel pitches reduce voxel dimensions relative to feature size, mitigating density averaging errors during volumetric measurement routines. Sub-voxel edge detection algorithms estimate actual surface boundaries by analyzing grey-scale gradients across neighboring voxel groups.
Spatial Resolution
Voxel size selection directly dictates the accuracy of volumetric void fraction analysis in power semiconductor solder joints. Undersampling fine feature boundaries causes false pass or fail classifications during automated inline X-ray inspection runs. Calibration phantoms establish dimensional measurement uncertainty limits under specific voxel resolution configurations.
