Cone-beam computed laminography for flexible three-dimensional analysis of stacked microvias in multilayer printed circuit boards

Abstract

While conventional computed tomography (CT) is widely used in nondestructive analysis applications, the scanning geometry poses limitations on objects with high aspect ratios, such as printed circuit boards (PCBs), which significantly reduce image quality. Alternatively, computed laminography (CL) techniques are being developed to overcome these challenges by granting additional flexibility of the scan geometry. For this study, the capabilities of a laboratory cabinet x-ray system are extended to perform CL scan acquisitions. Key issues regarding the system geometry are evaluated and calibration techniques are implemented to ensure CL reconstruction accuracy, which is particularly sensitive for high-magnification applications. Results using the CL method are evaluated against the traditional cone-beam CT method which shows improved image quality for the nondestructive inspection of stacked microvias buried within large PCBs. This study also uncovers the particular issues with our system geometry calibration that influence the quality of the reconstructed CL images. Application of these results suggest that cone-beam CL is an effective alternative to conventional CT when inspecting fine features within high aspect ratio objects.