High-precision alignment system of machine vision based on Hough transform

As the integrated circuit(IC) characteristic size continues to decrease, the number of I/O pins is increasing. For high-density packaging, especially in 2.5D/3D packages, fast and accurate alignment of electronic components and substrates is critical. A precise optical vision alignment system was set up by using the high precision charge coupled device (CCD), and the Hough transform algorithm was utilized to calibrate the chip and the substrate. The image captured was preprocessed to remove the noise, and the alignment marks were extracted by using morphological edge detection method, and 4 sets of parallel straight lines were obtained by Hough transform. Finally, the displacement and the rotation angle of the substrate were calculated and the alignment was completed. The running time of the Matlab program is about 4.2 s, the rotation parameter error is less than 1.2 °, x and y axis translation errors are less than 1 pixel. The experimental results demonstrate that the optical visual alignment system based on the Hough transform algorithm can realize chip and substrate alignment quickly and accurately to meet the IC packaging requirements.