EM Modeling: The Impact of Copper Ground Pour on Loss and Impedance


Reading time ( words)

This article briefly introduces the general purposes of copper ground pour on printed circuit boards. Subsequently, the impact of copper ground pour on PCB channel loss in terms of insertion loss and impedance in terms of time domain reflectometry (TDR) is studied with electromagnetic modeling using Mentor HyperLynx.

Introduction

Copper ground pours are created by filling open, unpopulated, or unrouted areas on outer layers of the PCB with copper. Subsequently, copper fill is hooked up to ground planes on inner layers with stitching vias as depicted in Figure 1. Copper ground pours on outer layers provide extra shielding against electromagnetic radiation by signals on inner layers. Besides that, copper pour also serves as a heat sink for the voltage regulator module on PCBs. In terms of manufacturability, copper pour reduces the possibility of PCB warpage during reflow by balancing the amount of copper on each side of the PCB.

Yee-fig-1.jpgHowever, copper ground pour comes with some disadvantages, as there is a change in impedance of PCB trace adjacent to ground pour (i.e., impedance decreases when copper pour becomes closer to the PCB trace). As a result, the impedance mismatch contributes additional PCB loss to the transmission line at a high-frequency range.

Analysis and Results

To study the impact of copper pour on PCB channel loss in terms of insertion loss and impedance in terms of TDR, five models of 1” single-ended microstrip listed in Table 1 were created. The simulation topology is shown in Figure 2. For model 1A, a microstrip trace 5 mils wide and 1 oz. thick is laid out 2.65 mils above the reference plane insulated by low-loss dielectric substrate material. This trace is sandwiched between two ground traces on the same outer layer. The spacing between each adjacent ground trace and the signal trace is 1x the signal trace width. Meanwhile, the spacing between each ground and signal trace is set as 2x, 4x, 6x, and 8x for model 1B, 1C, 1D and 1E, respectively.

To read this entire article, which appeared in the April 2019 issue of Design007 Magazine, click here.

Share




Suggested Items

Electronics vs. Physics: Why Vias Don’t Get Hot

12/06/2022 | Douglas Brooks, Consultant, and Johannes Adam, ADAM Research
Most of are aware that when we pass an electrical current through a trace (conductor), the trace will heat up. This temperature increase is caused by the I2R power loss dissipated in the resistance of the trace. The resistance of a copper trace is mostly determined by its geometry (cross-sectional area), and there are lots of studies trying to look at the relationship between the current down a trace (of known size) and the resulting temperature of the trace. But the situation is much more complicated than this. There are physical properties that exist that result in helping to cool the trace. These properties are usually a combination of conduction of the heat away from the trace through the material, convection of the heat away from the trace through the air, and radiation of the heat away from the trace.

My Experience With Maxwell

11/23/2022 | Happy Holden, I-Connect007
I was first introduced to James Maxwell in 1967 as a college student. I had to decide whether I would take the Maxwell fields course or the switching and coding course. Being a chemical engineering major with a co-major in control theory, I had heard about the trials and tribulations of the infamous Maxwell fields course.

Sunstone’s Matt Stevenson Shares Insights From New PCB Design Book

10/27/2022 | Nolan Johnson, I-Connect007
There’s designing the “perfect” circuit board and then there’s designing a board that is “perfect for manufacturing.” While seasoned designers and design engineers understand many of the nuances, PCB fabricator Sunstone Circuits has just published a new book specifically for new designers who have the knowledge of design but are still learning what it means to get the board manufactured. Sunstone’s Matt Stevenson takes the reader through a series of situations that should help clarify what’s happening in the fabrication process and how to adjust a board design to be better suited for manufacturing.



Copyright © 2022 I-Connect007 | IPC Publishing Group Inc. All rights reserved.