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[SOLVED] Trace vs Plane on Multi-Layer Board

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Jun 12, 2009
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Designing a 4-layer board (signal+pwr, gnd, signal+pwr, gnd), and I have some newbie doubts about the best option to connect different connector's pin or IC's pad to power lines, or sometimes to different signals. Board has different parts: Power, MCU & RF.

The main issues I have:

  1. Power at connectors. Which is the design guideline to right connect these pads? Will this type connection create EMI which affect to RF module?
  2. Power planes instead of traces. Which is the design guideline for routing at this situations? I think plane, instead of traces, will be better to reduce EMI and impedance, but I'd like to have a second option due to I'm worried about how it would affect to RF.
  3. Best layer for planes. I would have to create several planes to connect different voltages on top layer, is this suitable? On the internal signal layer, there's only a power plane and trace.

Power connections can be regarded as a DC signal with a AC component caused by the current consumption of the switching digital components. Make sure to route them in a plane, and add proper decoupling caps at chokepoints. The problem with planes attached to connectors with thermal reliefs is that you're creating a sudden change in impedance, which will indeed create large amounts of EMI if you're running an AC current through them. So again, decoupling with low ESR tantalum capacitors can be a good solution there.

As long as none of the power EMI or its harmonics are close to the frequency of your RF module, it should be fairly robust against interference. If necessary you can add an extra filter to the RF input, but this will of course also attenuate the useful signal.
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Thanks ArticCynda!

I'll take your comment into consideration in order to avoid EMI.


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