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40 The PCB Design Magazine • October 2017 for the 1-mil HK04J25 lami- nate example. Note that the resistance is given so far at zero frequency, whereas the starting point of the induc- tance is calculated at infinite frequency. The calculations assume that at DC the cur- rent penetrates vertically the plane thickness uni- formly (large skin depth), but at infinite frequency the current flows only on the facing surfaces of the planes (very small skin depth). At interim frequencies the current penetration de- pends on the ratio of the skin depth and conductor thickness. At each frequency we can calculate an effective plane separation, which is the dielectric thickness and the sum of the equivalent layer thickness values in the upper plane and lower plane. Similar calculations can be applied to obtain the Figure 5: HK04J25 Dk(f) and Df(f) as a function of frequency (on the left) and C(f) and G(f) as a function of frequency for a one square inch of laminate (on the right). Figure 6: Self-impedance magnitude in the middle of a 10" x 10" FR-4 dielectric sheet between one ounce copper planes. The parameter is the dielectric thickness. CAUSAL POWER PLANE MODELS