3D Solder Joint Reconstruction on SMD Based on 2D Images

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Automated optical inspection (AOI) systems are commonly used in PCB manufacturing. The use of this technology has been proven as highly efficient for process improvements and quality achievements. The most challenging point in inspection of surface mounting devices (SMD) is the component solder joints, due to their specular reflects. Several studies have been made to improve this situation. This paper presents an algorithm for 3D solder joint reconstruction (3D-SJR). The criteria used in the classification of the solder joints was the IPC-A-610D (Acceptability of Electronics Assemblies).

One of the most common technologies used in PCB manufacturing is surface mounted technology (SMT). By employing SMT, the production process speeds up, but the risk of defects also increases due to component miniaturization and denser packing of boards. In these conditions, the failure detection has become critical for any SMT manufacturing process. AOI systems for PCBs have become a proven solution, replacing the traditional human-based inspection method.

Historically, the primary place for AOI systems has been after solder reflow or post-production because post-reflow AOI systems can inspect for most types of defects (component placement, component polarity, solder shorts, missing solder, etc.) at one place in the manufacturing line with one AOI system. Hence, the faulty boards are reworked before they are sent to the next process stage.

Solder joint inspection has been a critical issue for quality control, mainly due to their specular reflections. AOI systems have been faced with the same difficulty for solder inspection. In order to improve the solder joint inspection and classification, structured light solutions have been used.

With structured light solutions, a low angle illumination ring improves the solder joint classification. These light systems have proven to be a very good lighting solution for SMT inspection and solder analysis. Some studies using structured light and advanced light reflection theories have been developing 3D reconstruction of solder joint shapes.

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 measurable dimensions related to component position and solder fillet size.

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Editor's Note: This article originally appeared in the June 2016 issue of SMT Magazine.



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