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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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Connect the Dots: Designing for Reality—Electroless Copper
08/28/2024 | Matt Stevenson -- Column: Connect the DotsRoll up your sleeves because it's time to get messy. In a recent episode of I-Connect007’s On the Line with… podcast, we discussed electroless copper deposition. This process deposits a copper layer into the through-holes and vias of what will eventually be a PCB. Electroless copper deposition feels like a black box to many people. It sort of looks like a black box, too. The boards go in one side, come out the other, and emerge differently. So, let's crack open that black box and look inside.
Maximizing ROI Through Better Wet Process Control
08/20/2024 | I-Connect007 Editorial Team“When things get out of control, the variation in your wet process begins,” says Mike Carano,. “Just because they look like good boards and may even pass electrical test, it does not necessarily mean you have good boards. Once the chemistry is headed toward the right or left side of the process control parameter cliff, the plating is compromised. If the copper is thinner than it should be, when the customer puts it into service, the board may fail after 500 cycles vs. the requisite 1,000 or 2,000 cycles. The root cause issue is that you plated 7/10ths of a mil of copper instead of one-mil of copper because you were not controlling your process. The fact that you passed your own electric test becomes inconsequential.”