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Below is the bottom layer of a 4 layer PCB.The stack up is SIG-GND-Power-Signal.

You can see that there is a floating ground whose some portion is not connected to GND plane.

I have shown that in red color. The portion connected to GND plane is shown in violet color.

May I know keeping ground floating as shown in red color will cause any emi emc or SI issues.

enter image description here

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  • \$\begingroup\$ Looks like it's connected to GND a the left. \$\endgroup\$
    – MiNiMe
    Oct 9, 2023 at 9:22
  • \$\begingroup\$ If the purple via is connected to GND, surely the red part is too? \$\endgroup\$
    – jonathanjo
    Oct 9, 2023 at 9:22
  • \$\begingroup\$ Yes RED part is connected but what I mean is there is no via in the red portion.will it cause any issues.It was connected to GND only at the violet area .No via to GND after that. \$\endgroup\$
    – Confused
    Oct 9, 2023 at 9:25
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    \$\begingroup\$ I recently watched Rick Hartley "How to Achieve Proper Grounding" which helped me enormously in understanding what's going on with ground planes. NB the video has some sound issues, but he repeats the missing part. (Thanks @RussellH !) \$\endgroup\$
    – jonathanjo
    Oct 9, 2023 at 10:02
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    \$\begingroup\$ Surely it is worse that the giant "GND" island with only one via in it and no direct connection to the bulk of the pour, than a peninsula that has no connection (nominally no current flow at all)? Seems to me, all three traces from the SMD-8 component could be moved to trivially solve both concerns. \$\endgroup\$ Oct 9, 2023 at 11:26

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To me it looks like it is still connected between the 2 IC pads.

In general: Having floating copper Islands (copper with absolutely no connection to any other signal) in-between Signal traces is bad with regards to signal integrity / crosstalk. At high frequencies (or fast risetimes) the copper island may behave like an antenna and the signals might couple into each other. So, if it really isn't connected either remove it or make sure it is connected to GND as well.

Edit after OP comment: At that scale it should not cause any issues, especially because the bit you circled doesn't carry any return currents. But if the partially isolated area was larger or you'd expect some return current to flow through it you should try to add a few additional vias there.

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  • \$\begingroup\$ The red portion is connected to GND by the via shown in violet color. You can see that there is no via in the red portion.Is that a good method. If we can place the one more via in the end of red portion it will be good. Please correct me if I am wrong. \$\endgroup\$
    – Confused
    Oct 9, 2023 at 9:35
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    \$\begingroup\$ @Hari Right now it is good to go (should work with no problems), if you want it to be perfect you can try to fit another via in the red area. But as I said the way you have it now should work just fine. \$\endgroup\$ Oct 9, 2023 at 9:49

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