An all-optical imaging method integrated laser-induced ultrasound and Fabry–Pérot acoustic detector for NDT of multilayer PCBs with subsurface defects

With the increasing structural complexity and layer count of printed circuit boards (PCBs), subsurface defects such as delamination and disbonds have become more prevalent. Precise detection of subsurface defects in multilayer PCBs remains a significant challenge. To address this, this study proposes a non-contact imaging method that integrates laser-induced ultrasound with a Fabry–Pérot acoustic detector, offering high-sensitivity for identifying subsurface defects. Two PCB specimens containing artificial defects were detected using this imaging method. The results indicate that the proposed imaging method can effectively detect subsurface defects with a diameter-to-depth ratio (D/d) as low as 0.72. Furthermore, quantitative estimation of defect thickness was achieved based on ultrasonic propagation characteristics. The spatial location, size, and distribution of defects are also clearly visualized through optical-acoustic fusion imaging, demonstrating the potential of multi-source data fusion.