User's Manual

System Manufacturing

5-4 Intel

820 Chipset Design Guide

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.

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.

Figure 5-2. (a,b) Microstrip and Stripline Cross-section for 28 Ω Trace

4.5 mils

2.1 mils

6 mils

18 mils

10 mils

a) Microstrip Cross-Section for 28 Ohm trace

b) Stripline Cross-Section for 28 Ohm trace

5 mils

1.2 mils

5 mils

13.5 mils

6 mils

7 mils

1.2 mils

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

W181818181719

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

r 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