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Does Copper Pour on a Signal Layer Decrease Signal-To-Signal Isolation?
April 7, 2022 | Steve Hageman, Analog HomeEstimated reading time: 1 minute

Does putting a ground pour on PCB signal layers make the isolation better or worse? It can go either way, but with the proper knowledge and application, this technique will improve your designs.
In this article, I’ll discuss how to simulate trace-to-trace isolation with true electromagnetic simulation software. We’ll also cover a variety of rules of thumb that can help you stay away from trouble.
Fact or Fiction?
Recently an acquaintance told me, “I have heard that putting a copper pour on a signal layer between traces actually makes the isolation between the traces worse.” I grabbed one of my RF boards and said, “If that is so, then how do all these RF boards that I have done with co-planar waveguide over ground manage to function? They all have copper pours on the signal layer, and they work to very high frequencies.”
Since co-planar waveguide over ground (CPWG), which is essentially “pouring copper on a signal layer,” is used for a lot of RF work, and is proven to work for very high-performance RF circuits, how did this contradictory opinion catch on in the industry?
To investigate this, I used a one-inch section of 50-ohm microstrip consisting of an aggressor trace from ports 1 to 2 and a victim trace running in parallel from ports 3 to 4. I used typical values for the dimensions as might be on a real PCB. The trace width is 20 mils, with a spacing of 60 mils from center to center, over an FR-4 substrate, 9.5 mils thick, with a modeled Er of 4.4.
To read this entire article, which appeared in the March 2022 issue of Design007 Magazine, click here.
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Sweeney Ng - CEE PCBSuggested Items
Statement from the Global Electronics Association on the July 2025 Tariff on Copper Foil and Electronics-Grade Copper Inputs
07/31/2025 | Global Electronics AssociationWe are disappointed by today’s decision to impose a 50% tariff on imported copper foil and other essential materials critical to electronics manufacturing in the United States.
Considering the Future of Impending Copper Tariffs
07/30/2025 | I-Connect007 Editorial TeamThe Global Electronics Association is alerting industry members that a potential 50% tariff on copper could hit U.S. electronics manufacturers where it hurts.
Connect the Dots: Sequential Lamination in HDI PCB Manufacturing
07/31/2025 | Matt Stevenson -- Column: Connect the DotsAs HDI technology becomes mainstream in high-speed and miniaturized electronics, understanding the PCB manufacturing process can help PCB design engineers create successful, cost-effective designs using advanced technologies. Designs that incorporate blind and buried vias, boards with space constraints, sensitive signal integrity requirements, or internal heat dissipation concerns are often candidates for HDI technology and usually require sequential lamination to satisfy the requirements.
OKI Launches Rigid-Flex PCBs with Embedded Copper Coins Featuring Improved Heat Dissipation for Space Equipment Applications
07/29/2025 | BUSINESS WIREOKI Circuit Technology, the OKI Group’s printed circuit board (PCB) business company, has developed rigid-flex PCBs with embedded copper coins that offer improved heat dissipation for use in rockets and satellite-mounted equipment operating in vacuum environments.
Designers Notebook: Basic PCB Planning Criteria—Establishing Design Constraints
07/22/2025 | Vern Solberg -- Column: Designer's NotebookPrinted circuit board development flows more smoothly when all critical issues are predefined and understood from the start. As a basic planning strategy, the designer must first consider the product performance criteria, then determine the specific industry standards or specifications that the product must meet. Planning also includes a review of all significant issues that may affect the product’s manufacture, performance, reliability, overall quality, and safety.