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30 PCB007 MAGAZINE I OCTOBER 2025 D R I V I N G I N N OVAT I O N Alignment is especially complex because of the flexible portion of the board, which can bend and move easily. Alignment systems, such as post-etch punch machines, must be designed to work with these delicate materials. It's also crucial to remember that flexible and rigid materials behave differently under thermal stress— stretching and shrinking at different rates dur- ing lamination and prior processes. The first step in managing this is to gather statistical data about these deformations using X-ray systems. Produc- tion can then perform one of two compensation types, or preferably both for complex boards: • Compensate during direct imaging: Each inner layer can be compensated individually during the direct imaging step by making adjustments for material type, copper density, layer position, and other factors. • Compensate during drilling: Compensation can also be applied during the drilling operation, which is especially easy if the drilling machine is equipped with CCDs and individual tables. This standard approach, also vital for HDI boards, is sometimes more critical in rigid-flex production because of the very different behaviors of the rigid and flex layers. Optical Operations Engineers must carefully adapt optical processes, including direct imaging and laser cutting, for rigid- flex materials. For direct imaging, machines need to handle thin flex layers without causing damage. While manual loading is an option, automated machines require highly adaptable, adjustable grippers that can handle such delicate materials without stress. After lamination, these mixed-material boards are never perfectly flat, so the machine must be equipped with an auto-focus system and Z-axis control for each print head to adapt to the uneven surface and maintain a sharp exposure. At the same time, it is often necessary to cut cov- erlays or contour the final shape of the flexible lay- ers. Typically, a laser cutting machine equipped with a UV-nanosecond or a pico green laser source does this. While a UV-nanosecond laser is often suffi- cient for special cases where cutting quality is crit- ical, the pico-green source provides the best results with minimal carbonization. The science behind this is that a laser beam is pure energy, and energy A f l ex b o a rd ex p o s e d by S c h m o l l M D I - F l ex . ▼ S c h e m e d e m o n st rat i n g t h e Z- a x i s o n t h e p r i nt h e a d . ▼