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74 The PCB Magazine • March 2014 A second study measured the impact of a flat innerlayer treatment with an 18 µm (1/2 oz./ft²) thick ultra-flat BF-HFI-LP2 foil, almost no profile copper foil with the primer coating (BF-ANP-PA) and thick reverse treated foil HFZ- B on the insertion loss. The study was using a very low-loss resin system (Panasonic Megtron 6) for high-end ap- plications. Details of this study are shown in Figure 10. Based on a reference board designed by Cis- co, all measurements using the Cisco S3 meth- ED-COPPER FOILS FOR HIGH-SPEED DIGITAL PCBS continues Figure 8: insertion loss study #1. Figure 9: innerlayer oxide on a flat profile foil.