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38 DESIGN007 MAGAZINE I JUNE 2022 PCB designs that are generally well- grounded (that is, there are ground vias con- necting the planes in multiple places) create a Faraday cage that functions to contain inter- nal resonances and energy that might be avail- able to radiate from the edge of the board. Power distribution networks that are well- bypassed across the entire area of the planes also help suppress resonance. Copper pour and via stitching are unnecessary in many digital designs. Copper pour is not the magic bullet that will solve all your EMC problems. Pouring copper randomly to fill up space may create additional issues. Proper design prac- tice should be applied rather than just random copper. Key Points • e myth of copper pours is fueled by ref- erence designs that seem to persistently use this old RF design technique. • Copper pours are sometimes used, incor- rectly, simply to fill in the unused space on a board. • e CAM engineer may add copper thieving patterns to balance the copper distribution on a layer. • Floating (unconnected copper) is a real hazard for signal integrity. All copper pours must be connected to ground or power net. • A ground pour that is not accompanied by grounding vias can become a conduit for crosstalk between the traces on either side of the ground shape. • By creating the copper thieving as part of the ground net and configuring it as a solid plane, you can assist with providing a well-defined return current path. • Any additional planes must be positioned and spaced correctly, so they do not have a negative effect on the signal integrity of the board. • A ground pour on a microstrip layer changes the transmission line from microstrip to grounded coplanar wave- guide. • e characteristic and differential imped- ance of the transmission line is lowered by using this technique. • CPW combines the EM fields in a more localized manner than does microstrip, thus reducing spurious coupling, radia- tion, and dispersion. • Microstrip can radiate. However, with the fields confined between ground planes, stripline does not. • When copper pours come into proxim- ity of critical signal traces (Figure 3) the impedance is reduced by 2–3 ohms. • is will convert differential mode signals into common mode signals at these points, impacting signal integrity. DESIGN007 Resources 1. Beyond Design: "To Pour or Not to Pour," "Com- mon Symptoms of Common Mode Radiation," by Barry Olney. 2. An Altium Designer blog, "Copper Pour and Via Stitching: Do You Need Them in a PCB Layout?" Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Australia, a PCB design service bureau that specializes in board-level simulation. The company developed the iCD Design Integrity software incorporating the iCD Stackup, PDN, and CPW Planner. The software can be downloaded at www.icd.com.au. To read past columns or contact Olney, click here.