Intel VC820 Design Guide - Page 148
Impedance Calculation Tools, 5.3.8 Testing Board Impedance,
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System Manufacturing Figure 5-2. (a,b) Microstrip and Stripline Cross-section for 28 Ω Trace a) Microstrip Cross-Section for 28 Ohm trace 10 mils 6 mils 18 mils G S G 4.5 mils 2.1 mils b) Stripline Cross-Section for 28 Ohm trace 6 mils G 5 mils 5 mils 13.5 mils S 1.2 mils 7 mils G 1.2 mils 1.2 mils Note: Don't forget ground floods and stitching 5.3.7 Impedance Calculation Tools The 3D Field Solvers (e.g., those by HP, Ansoft, Sonnet, and Polar) are the most accurate for calculating impedance. Z calculators based on equations (zcalc) are also fairly accurate. The differences are shown in Table 5-2. Table 5-2. 3D Field Solver vs ZCALC #1 #2 #3 #4 #5 #6 H 4.5 4.5 4.2 4.8 4.5 4.5 W 18 18 18 18 17 19 W1 18.1 18.1 18.1 18.1 17.1 19.1 T 1.4 2.8 1.4 1.4 1.4 1.4 εr 4.5 4.5 4.5 4.5 4.5 4.5 Z0(3D) 29.0 28.4 27.6 30.4 30.2 27.9 Z0(zcalc) 29.1 28.7 27.7 30.4 30.2 28.0 5.3.8 Testing Board Impedance The Intel Impedance Test Methodology Document should be used to ensure boards are within the 28 Ω ±10% requirement. This document can be found at: http://developer.intel.com. 5-4 Intel®820 Chipset Design Guide