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We are using Murata's 4MHz ceramic resonator (CSTCR4M00G53-R0) in one of our designs and request help in PCB layout design around the ceramic resonator. The below Murata's FAQs page suggests not to place any GND plane under the ceramic resonator. Picture in page is attached below.

https://www.murata.com/en-us/support/faqs/products/timingdevice/ceralock/cct/cc0010

enter image description here

We are using a 4 layer PCB with continuous GND plane in layers 1,2 & 4 and continuous power plane in layer 3.

Please help us with the questions below:

  1. Should we provide a copper clearance area under the ceramic resonator in the inner layers also i.e. layers 2, 3 & 4, or is it sufficient if we just clear the GND plane in the top layer?

  2. Is it recommended to place GND stitching vias around the tesonator (green dots as shown in below image) or should we completely avoid any vias around the resonator?

enter image description here

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    \$\begingroup\$ The stitching vias should be fine. The ground area can capacitively couple noise onto the ground plane. The capacitance can also cause instability in the oscillator. Just place a small keepout under the clock chip and IC pins. \$\endgroup\$
    – Aaron
    Jul 3 '19 at 16:31
  • \$\begingroup\$ @Aaron Thank you for suggestions. Are you suggesting to maintain a keepout in inner layers also right under the resonator / oscillator? \$\endgroup\$
    – Andrea
    Jul 4 '19 at 11:35
  • \$\begingroup\$ yes. I would do a keepout for all the layers under the oscillator. Think about it, there are no other ways to have ground/power underneath the traces as they've shown them. Therefore it is the planes. \$\endgroup\$
    – Aaron
    Jul 4 '19 at 18:40
  • \$\begingroup\$ @Aaron Thanks a lot for help. We tested boards today with out ground/power planes underneath and they are working perfect. \$\endgroup\$
    – Andrea
    Jul 16 '19 at 18:09
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You can clear the copper under it on all layers. The hole this leaves is quite small, I doubt it would have any effect. The ground stitching around the area is a little bit like a shield. They don't want any fields developing across the gap which might interfere with the resonator. Personally I would use the vias but skip every other one, I don't think you need that many.

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