Microstrip Copper Pour and Losses

[@DeadCatX2]

Rick Hartley recommends tying the copper pours to the alternate polarity of the underlying reference plane, to increase interplane capacitance because such layers are often very closely spaced. Your talk refers to ground pours, though. How would having a power pour on the top layer affect the coplanar waveguide of a microstrip referencing a ground plane? Would the fields "prefer" coupling to the ground plane because the pour powers would require the return current to pass through a bypass cap?

[@Zachariah-Peterson]

I'm familiar with this strategy, Lee Ritchey has stated he does the same thing. If you're designing to just use copper pour as a mechanism to increase plane capacitance, rather than using it for a controlled impedance circuit, then it's an appropriate way to use pour. Eric Bogatin has told me he disagrees with any use of ground pour and says there is no real usage for it ever, but that's another matter I'll be discussing with him in an upcoming video :). I think both groups are right.... the capacitance view is technically correct, but that's not necessarily implemented to solve a specific problem. Bogatin says it's never needed, and he's probably technically correct too because if you do the board design right, you might not need the extra capacitance anyways, so why bother? I think it's a silly thing to argue about because, 9 times out of 10, it doesn't cause the board to fail. Conversely, if you have an existing EMI problem in your board and you didn't include copper pour, then simply adding in the copper pour probably won't solve the problem, the root cause is either your stackup, grounding, or routing. I approach copper pour from the RF perspective anyways, where you do need it in specific types of RF structures you design. If copper pour and stitching vias didn't work, we would never have used it as on-board shielding in most cell phones for the last 2 decades. In terms of what happens if you bring in power pour vs ground pour, you would still have the same capacitive effect because a signal traveling along a trace would be switching between two states, it's not a constant voltage. The capacitance is always there, but it doesn't create displacement current unless there is some dV/dt across that capacitance like you would have in a switching signal. I believe in the case where you have signal level being larger than the pour voltage level, then you would still have the same return current effect, it will then just couple capacitively back to GND through bypass/decaps and through the parasitic capacitance. If the polarity across that gapped capacitance is reversed, then the polarity of the displacement current is also reversed. It's more a matter of "what direction does the current flow".

[@saeidesekhavati1518]

EXCELLENT information, thank you!

[@AltiumAcademy]

Glad it was helpful!

[@adityamody8942]

what happens when you have a 20Hz to 20KHz signal with 20Vpp how would it be affected if the width is 0.5mm. The signal is not Digital but Audio

[@Zachariah-Peterson]

At those frequencies the losses due to copper and the dielectric are barely noticeable. This is because those losses are proportional to frequency, so they are much larger with fast digital signals and RF signals, where the frequency content is in the high MHz range or GHz range. At audio frequencies, the dominant loss mechanism is the DC resistance of the traces. If you are doing anything with amplifiers, you are basically designing a power system that must operate at those frequencies so it will tend to have much larger rails for those audio signal becuase this will reduce the DC losses on those nets.

[@adityamody8942]

@@Zachariah-Peterson thank very much this was great help, will post question 👍

[@keynaanmedia5329]

I like 3D pictures and video simulations examples than blackboard drawings