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I have a PCB where there is mounted a microphone, on page 17 in the datasheet, there is a PCB landpattern with broken GND ring.

I have used this landpattern and routed traces through the opening.

But the microphone has an pad there, so directly above the traces there is soldermask and then the pad.

I was thinking if this could be a problem, that the PAD might short with the traces, or should the soldermask be able to keep the isolation ?

Below is a picture of my routing, the grid is 0.1mm.

microphone routing

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  • \$\begingroup\$ This shouldn't be a problem. But I would place some GND via on the lower part of the ring as well. \$\endgroup\$ – Botnic Jan 31 '17 at 8:20
  • \$\begingroup\$ I agree with Botnic. You can use a bit of silkscreen over the track as extra protection if you are worried. \$\endgroup\$ – Matthew Jan 31 '17 at 14:19
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To quote the linked datasheet:

Note that in both of these patterns, the solid ring around the sound port is still present; this ring is needed to ground the microphone and for acoustic performance. The pad on the package connected to this ring is ground and still needs a solid electrical connection to the PCB ground. If a land pattern similar to Figure 16 or Figure 17 is used on a PCB, make sure that the unconnected rectangle on the bottom of the INMP521 is not placed directly over any exposed copper. The ring on the microphone is still at ground, and any PCB traces routed beneath it must be properly masked to avoid short circuits.

As it says, avoid exposed copper. Standard solder mask should be sufficient to insulate traces from the ground ring on the device. If in doubt, you can use vias and put the traces on another layer.

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