SMT007 Magazine

SMT-June2016

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84 SMT Magazine • June 2016 tion and solder analysis. Some studies using structured light and advanced light reflection theories have been developing 3D reconstruc- tion of solder joint shapes [6-8] . IPC established the A-610 document to help manufacturers achieve the highest possible SMT production quality. The standard specifies three classes of electronic devices, depending on how mission critical the final application is. For each class, IPC-A-610 defines assembly of component packages onto PCBs using measur- able dimensions related to component position and solder fillet size [9] . IPC-A-610 rules specify that the solder joint should reach at least 25% of the component electrode height, however 2D AOI systems aren't capable of measuring the height of the solder joint. The measurement of such characteristics will require a 3D measurement system [10] . The proposed approach presents a 2D AOI system using the 3D-SJR method, for improving solder joint classification (Figure 1). 2D Image Acquisition The image acquisition system was installed in the SMT manufacturing line. The equipment used on this study was the VT-RNS-II from OM- RON [12] . Figure 2 shows an RGB image obtained in the image acquisition stage. The illumination system used in the acqui- sition step consists of three rings of LED lights, each ring with a different LED color and placed at a different angle (Figure 3). Phong Reflection Model The proposed approach uses the Phong re- flection model to analyze the solder joint area. The Phong reflection model (1) has three com- ponents: the ambient light reflection (Ia), the diffuse light reflection (Id) and the specular light reflection (Is). 1 Figure 1: Block diagram of the proposed approach. Figure 3: Light rings [12] . Figure 2: Initial image. 3D SOLDER JOINT RECONSTRUCTION ON SMD BASED ON 2D IMAGES

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