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78 PCB007 MAGAZINE I APRIL 2025 Inner Layer Exposure Before the introduction of direct imaging (DI) machines, contact exposure was the standard method. is process relied heavily on the alignment of phototools, making the overall accuracy dependent on the phototo- ol's condition. With direct imaging technology, depen- dency on photo tools has been eliminated, but achieving proper alignment now relies fully on machines. Since inner layers typically lack holes or fiducials—just copper—alignment must be established only by the machine itself. Mod- ern direct imaging equipment uses small UV markers integrated into the table, exposing fiducials from the bottom side while the main exposure system processes the top side (Fig- ure 1). ese fiducials later serve as reference points aer flipping the panel. Alignment of the Inner Layers ere are multiple methods for aligning inner layers before lamination. e three pri- mary approaches are: 1. Pin-lam: Pins in the press tools hold layers in position during lamination. 2. Mass-lam (without pins in press-tools dur- ing the lamination): Layup before lamina- tion could be done using: › A fully automated lay-up machine › A two-step lay-up process: a. First machine drills registration holes. b. e operator stacks the layers and pre preg on pins of second machine, then performs lay-up (via welding, riveting, etc.), and user removes the stack from the pins. Each method is viable, but the choice depends on several factors: • Required productivity levels • Pre- and post-processing needs • Accuracy requirements • Panel sizes • Compatibility with different materials • Capability to measure inner layers before lay-up • Maintenance requirements is topic alone needs a deeper discussion, and we will explore it further in future articles. X-ray Aer lamination, if pin-lam holes are not available or not used, X-ray registration is Simon Khesin Figure 1: Inner layer alignment fiducial, exposed by UV markers in the table during top side exposure, and recognized by CCD camera alignment during the bottom side exposure.