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92 DESIGN007 MAGAZINE I SEPTEMBER 2019 ferent nickel thickness were measured for cir- cuit dimension differences and nothing signifi- cant found. The thicker nickel will impact the capacitance in the gap coupled area. Thicker nickel decreases the conductivity in the gap coupled area, which is seen as a decrease in capacitance, that will shift the frequency up which relates to a lower extracted Dk. Addi- tionally, if Df was extracted, then the ring res- onator with the thicker nickel would report a falsely higher Df than the ring resonator using the thinner nickel, again, while using the same sheet of material. Conclusions Conductor loss is one of the components of PCB insertion loss and can be impacted by the final plated finish used for a circuit. There can be a substantial increase in insertion loss due to the final plated finish. This study explored the effects of the final plated finish on circuit insertion loss. Thin substrates were used to achieve good resolution among the different plated finishes used with the test vehicle, al- though if a thicker circuit was used, the mag- nitude of the curves shown in this study would be less. As a reference, that effect (of substrate thickness) can be seen in Figure 2. Designers should consider the effects of final plated fin- ish on insertion loss when predicting and sim- ulating circuit performance during the design phase of circuit development and choose final plated finishes according to performance re- quirements. DESIGN007 Acknowledgments I would like to thank Accurate Circuit Engi- neering for the fabrication of the circuits in- volved in this study. I would also like to thank MacDermid and Uyemura for their kind assis- tance with these plated finishes as well as ap- plying the plated finishes to several circuit sets. References 1. J. Coonrod, "The Effects of PCB Fabrication on High- Frequency Electrical Performance," IPC APEX EXPO, 2015. 2. J. Coonrod, "The Effect of Radiation Loss on High-Fre- quency PCB Performance," IPC APEX EXPO, 2014. 3. J. Coonrod, "Understanding the Variables of Dielec- tric Constant for PCB Materials Used at Microwave Fre- quencies," European Microwave Week, 2011. 4. A.F. Horn III, J.W. Reynolds, and J.C. Rautio, "Con- ductor Profile Effects on the Propagation Constant of Microstrip Transmission Lines," 1-Rogers Corporation, 2-Sonnet Software, IEEE Transactions on Microwave The- ory & Techniques Symposium, 2010. 5. J. Coonrod, "Managing Circuit Materials at mmWave Frequencies," Microwave Journal, Vol. 58, No. 7, July 2015. This paper was first presented at the IPC APEX EXPO 2019 Technical Conference and published in the 2019 Technical Conference Proceedings. John Coonrod is technical marketing manager at Rogers Corporation and an I-Connect007 columnist. Figure 11: Comparison of Dk extraction using microstrip ring resonator with ENIG plating having different nickel thickness.