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March 2014 • The PCB Magazine 75 od up to 25 GHz compare the three different copper foil profiles (Rz between ~1–1.2µ and ~3.6–4µ) and five different innerlayer oxide treatments from MEC generating significantly different roughness on the foil's shiny side. 50Ω single-ended striplines and 16-inch striplines produced the following results: While using the same innerlayer treatment, a significant difference is measured between an ultra-flat profile foil and a conventional reverse treated copper foil. By using the same ultra-flat copper foil, the innerlayer treatment producing a Ra of only 0.04 µm generates up to 11% lower insertion losses compared to a conventional oxide treat- ment with a Rz of 1.5 µm. The losses for the primer coated ANP cop- per foil type were very close to the ultra-flat BF- HFI-LP2 foil, but presented higher peel strength compared to the other foil types. Summary and Conclusions For high-end applications using very low- loss resin chemistries, the usage of ultra-flat profile BF style copper foils is highly recom- mended for taking entire advantage of much lower conductor losses. In the near future, a primer-coated, almost no profile foil (BF-ANP-PA) may contribute to higher peel strength without impacting dielec- tric loss. For mid-loss resin systems, the relationship of required performance to cost is very likely the leading decision factor. PCB References 1. Cisco ® Global Cloud Index. 2. BPA Report n°985. 3. A. F. Horn III, J. W. Reynolds, P. A. LaF- rance and J. C. Raution, ''Effect of conductor profile on the insertion loss, phase constant, ED-COPPER FOILS FOR HIGH-SPEED DIGITAL PCBS continues Figure 10: insertion loss study #2.

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