Printed Circuit Design & Fab - June 2008 - (Page 34)

DFA reliability for Complex Designs Advanced AOI techniques provide manufacturers and OEM customers with exceptional inspection reliability. by ZuLKI KAHN AoI – Defining Automated optical inspection (AOI) technology is making significant progress as PCB designs continue to pack in more circuitry per square inch and create new inspection challenges. Nowhere is this felt more than in assembly. Both designers and EMS providers need to stay abreast of the latest advances in AOI tooling to ensure that designs can be inspected to yield highly reliable assembled products. Precise optics, advanced AOI algorithms, powerful computing, and easy-to-read graphical user interfaces (GUIs) are critical to the success of PCB inspection whether it is at the bare board level or in pre- post-assembly. The common goal among AOI system manufacturers is to improve lighting, computing power, vision software, and signal-to-noise ratio (SNR). These improvements make AOI products more intelligent, flexible, and with far more repeatable results that are superior to human visual inspection. In AOI terms, SNR refers to the signal or image represented by a featured component and its markings of interest. Noise comes in a variety of forms that need to be suppressed to achieve a cleaner image. Lighting is a critical factor for managing SNR. In the case of post-assembly inspection, the AOI tool must have the capability to view all the features and markings of a component to efficiently perform an inspection. Appropriate light conditions amplify the features of interest and verify them, while suppressing any features considered noise. LED-based lighting, now standard for newer AOI gear, is stable and easily controlled. Older style incandescent and fluorescent lighting are still used in some newer systems. Further, the increasing complexity of PCB manufacturing is severely challenging AOI’s computing power. Hence, increasingly powerful data crunching capability is critical to acquiring an image, comparing it to a golden board, processing the inspection, and communicating the information to the 34 database. One of the biggest challenges is that all this computing needs to happen continuously and in real time. High-end AOI systems operate on 3-dimensional CAD data. They render an image in 3D to perform component verification for cracks or flaws, lead contamination or oxidization, scratches, and other defects. These advanced AOI systems use 4 to 6 cameras to capture an image the cameras translate the light pattern from the inspected component into an electronic image. FiGurE 1 shows an AOI image while the software is being “trained” to view a component and verify markings. In this process, the system uses progressive scanning to acquire a series of images and then compares them against each other. In this training sequence, the computer analyzes the image of the board’s features to exact specifications. Here, the “brains” of the AOI system is the vision computer and its software, where complex algorithms store details and verify FiGurE 1. AOI Image is shown while the software is being “trained” to view a component. Also shows component markings. JUNE 2008 printEd circuit dESign & fAB

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Printed Circuit Design & Fab - June 2008 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar Interconnect Strategies Final Finish Forum DFA/DFT Signal Integrity From the Field DFA Fab Basics Drill Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - June 2008

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