All-optical optical-acoustic fusion technology: A novel method for defect detection and 3D reconstruction in PCBs

Laser ultrasonic testing (LUT) offers high-resolution, non-contact and material-flexible detection. However, its point-by-point scanning mode limits efficiency, making it well-suited for detailed evaluation of critical regions while posing challenges for automated defect positioning and detection. To address this limitation, this study proposed an optical image-based positioning method, which integrated optical imaging and LUT for automated defect detection and 3D reconstruction in printed circuit boards (PCBs). Optical images are used for locating the detection region and guiding LUT scanning, and LUT results are fused with optical images to achieve intuitive defect visualization. An acoustic attenuation–based model is used for defect depth estimation, yielding an average error of 5.56 % in the detection region. Experimental results demonstrate that the proposed method accurately reveals both surface morphology and subsurface defect features. Quantitative comparison with infrared thermography (IR) shows that LUT provides higher imaging quality and improved depth-to-diameter detectability for subsurface defects. The fusion image achieves a positioning error of approximately 0.32 mm and an average IoU of approximately 0.643, demonstrating the feasibility of the system for 3D visualization.