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80 PCB007 MAGAZINE I APRIL 2025 How is X-ray Data Used? Once X-ray measurement data is available, it serves two equally important purposes in the PCB production process: 1. Compensating inner-layer exposure for the next batch: By analyzing registration devi- ations, manufacturers can adjust exposure parameters in subsequent similar produc- tion batches to improve alignment and reduce errors over time. 2. Correcting the drilling program for the current batch: X-ray data is used to align the drilling process to the actual position of the inner layers, ensuring greater accu- racy in via and hole placement. While exposure correction helps refine the overall process for future batches, drilling compensation is essential for achieving high precision within the same production batch. To perform corrections at the drilling stage, X-ray data (needed corrections for the drilling part program to better correspond to the position of the inner layers) must be somehow transferred accurately to the drill- ing machine. While data can be passed man- ually or through specialized soware, these methods have limitations—they allow data to transfer to the drilling machine but do not enable per-station compensation. Ensuring precise alignment at each sta- tion requires a more advanced process. In such a process, aside from drilling on X-ray two positioning base holes for the prism and slot, additional holes/fiducials for the individual alignment must also be drilled directly on the X-ray machine. is allows the CCD cameras on the drilling machines to recognize those reference holes at the panel alignment level or, if needed, within individual PCB zones. In such a process, the "data about the inner layers" (i.e., needed corrections for the drilling program) can be transferred to each individual station of the drilling machine indirectly via reference fiducials/holes that are drilled on the X-ray machine in positions which correspond to the inner layer misalignment picture. For multi-zone alignment, where a single panel contains multiple high-accuracy PCBs, the X-ray system must support full-table measurement and drilling, ensuring optimal registration across the entire panel. If multi- zone alignment is used, fiducials should be drilled not only at the panel corners but also in corners of each zone, allowing zone-spe- cific compensation. Mechanical Drilling Alignment Achieving precise registration on drilling machines requires CCD cameras for fiducial recognition (Figure 5). To achieve this on multi-station machines: • Each station must have independent CCD • A fully independent axis system is required Figure 4b: Pad-stack fiducials on a HDI PCB recognized by X-ray. Figure 4a: Layer-to-layer fiducials on a 74-layer PCB with a 10 mm thickness recognized by X-ray.