Spatial resolution of a laboratory based X-Ray cone-beam laminography scanning system for various trajectories

Abstract

Computed laminography (CL), a long established NDT method, is ideal for the non-destructive evaluation of plate-like structures, for which conventional computed tomography (CT) is less well suited. This paper demonstrates the feasibility of implementing raster CL on a Nikon Metrology custom build X-ray CT scanner without the need for specialised equipment. To provide a more principled way to demonstrate the widespread adoption of CL for defect characterization in plate-like structures, a test specimen was designed and manufactured from Polyoxymethylene (Delrin) that allows well defined features of different size and orientation to be characterized. The study highlights the relation between direction-dependent spatial resolution, feature geometry and scan trajectory. It demonstrates that high-resolution and highspeed in situ volume-imaging of plate-like structures with large aspect ratios is viable at levels that would be challenging via CT or alternative three-dimensional NDT methods.

Geometric calibration of a computed laminography system for high‐magnification nondestructive test imaging

“…CT operates using the attenuation coefficient of X‐rays transmitted through a material to form a 3D image. It effectively inspects a structure's interior by filtering the projection images acquired from various directions around the rotation axis and projecting them back [6,8–10]. However, CT equipment has limitations in imaging samples with platelike structures, such as ICs and multilayer printed circuit boards (PCBs) [1–3,6,7].…”

“…It effectively inspects a structure's interior by filtering the projection images acquired from various directions around the rotation axis and projecting them back [6,8–10]. However, CT equipment has limitations in imaging samples with platelike structures, such as ICs and multilayer printed circuit boards (PCBs) [1–3,6,7]. First, obtaining projection images by rotating a platelike sample does not provide sufficient projection information in a specific angular range according to the shape and thickness of the sample [3,5].…”

“…The importance of NDT increases as products, such as integrated circuit (IC) packaging, become smaller and the complexity of their structure increases [2]. In particular, using X-ray computed tomography (CT) is becoming increasingly popular, as it can reconstruct and analyze threedimensional images (3D) [1][2][3][4][5][6][7]. CT operates using the attenuation coefficient of X-rays transmitted through a material to form a 3D image.…”

“…However, CT Seung-Hoon Chae and Kihong Son contributed equally to this work. equipment has limitations in imaging samples with platelike structures, such as ICs and multilayer printed circuit boards (PCBs) [1][2][3]6,7]. First, obtaining projection images by rotating a platelike sample does not provide sufficient projection information in a specific angular range according to the shape and thickness of the sample [3,5].…”

“…Additionally, even if the projection images were acquired using high-energy X-rays with enough flux, differences in the X-ray transmission path length and its effects by scattering, beam hardening, and photon starvation, and so on, would significantly degrade the quality and spatial resolution of the reconstructed images. Second, a sufficient distance between the source and sample is required to avoid collisions, reducing the magnification and spatial resolution of the CT images [5,6]. One approach to overcoming the above limitations is rotational computed laminography (CL) [1][2][3][4][5], which is based on the relative motion of the X-ray source, detector, and sample.…”