An Optical Inspection System for the Solder Balls of BGA using Support Vector Machine Classification
In this paper, the Support Vector Machine (SVM) is utilized to classify the defective solder ball of ball grid array (BGA) so as to promote the accuracy and efficiency of the optical inspection. The terms of inspections include the ball displacement, the ball over scale, the ball undersize, the ball absence, and ball bridging. There are two step of the SVM processing: the training step and the real testing step. The SVM is more efficiency because of the calculation in testing step is no relation to the number of the input vector. As this point, SVM is fit to build up the high dimension input recognize system such as BGA inspection. From the real testing results, the Support Vector Machine is proved to properly identify and classify the shape defects. The two dimensional BGA optical inspecting system is implemented by Visual Basic as the developing tool incorporated with the Halcon's function which is the database of the image processing on Windows operation system. For the development of the processing procedure of the automatic optical inspecting system with the designed lighting system, the precise geometrical information of the solder ball is evaluated by the sub-pixel method to identify the shape of solder ball and its location under the BGA board is offset and rotated at any angle.
A Line-Based-Clustering Approach for Ball Grid Array Component Inspection in Surface-Mount Technology
In production processes that use surface-mount technology (SMT) for the assembly of printed circuit boards, automated optical inspection is widely employed to diagnose component defects. However, commonly used inspection algorithms can hardly meet reliability and time efficiency requirements simultaneously, especially when applied to the components of high-density and large-scale integration, such as ball grid array (BGA). In this paper, a novel approach is presented to inspect BGA component defects. An adaptive thresholding combined with modified  $(\varepsilon, \delta)$-component segmentation is first performed to extract the grayscale image of solder balls. A line-based-clustering method is then proposed to recognize ball array. Simultaneously, accurate position and orientation of BGA are obtained based on the recognition results. Finally, ball features are extracted to diagnose potential defects. The proposed algorithm is implemented on the host computer of Samsung SMT 482 machine. The results obtained show that the proposed approach is suitable for a vast majority of BGAs with different ball arrays and also that it is robust to interferences caused by the image segmentation. Furthermore, compared to Samsung's algorithm, it has significant advantages in time efficiency and high inspection accuracy under nonideal lighting conditions.
Synthesis of β-FeSi2 nanowires by using silicon nanowire templates
Si nanowires templates were grown by a Cu-catalyzed vapor–liquid–solid process and used for the preparation of β-FeSi2 nanowires on a Si substrate. The silicon nanowires were transformed into β-FeSi2 nanowires by annealing with additional source material containing FeCl2 and Si powder. In contrast to uniform Si nanowire templates along the direction, the synthesized nanowires were deformed irregularly. The electron diffraction pattern of the nanowires synthesized from the template corresponded to that of single-crystalline β-FeSi2 and the longitudinal direction of the nanowire was along the direction. The energy dispersive X-ray fluorescence analysis confirmed that the nanowire contained Fe and Si in an atomic ratio of approximately 1:2. The results confirmed that β-FeSi2 nanowires on a Si substrate were synthesized from the Si nanowire templates.Si nanowires templates were grown by a Cu-catalyzed vapor–liquid–solid process and used for the preparation of β-FeSi2 nanowires on a Si substrate. The silicon nanowires were transformed into β-FeSi2 nanowires by annealing with additional source material containing FeCl2 and Si powder. In contrast to uniform Si nanowire templates along the direction, the synthesized nanowires were deformed irregularly. The electron diffraction pattern of the nanowires synthesized from the template corresponded to that of single-crystalline β-FeSi2 and the longitudinal direction of the nanowire was along the direction. The energy dispersive X-ray fluorescence analysis confirmed that the nanowire contained Fe and Si in an atomic ratio of approximately 1:2. The results confirmed that β-FeSi2 nanowires on a Si substrate were synthesized from the Si nanowire templates.