PCB Crystal layout recommendations

[Nikos A.]

Hi guys,

I will integrate the MDBT50Q-1MV2 Bluetooth module into my design. According to the datasheet, a 32.768KHz crystal is required
https://www.raytac.com/product/ins.php?index_id=24
https://www.raytac.com/download/index.php?index_id=43
https://eu.mouser.com/ProductDetail/ABRACON/ABS05-32.768KHZ-9-T?qs=Pyu0ZBy%2FIJbsNYnIET1z3A%3D%3D

My PCB is a four-layer design with the (signal, gnd, pwr + ctlr, pwr + ctrl)
Beneath the crystal and the load capacitor, there is a solid ground plane (2nd plane).
I've read some design guides for routing the crystals and they recommend not routing signals on other PCB layers running directly below the crystal or below the traces to the X1 & X2 pins

Due to the limited routing space, I routed some control signals (to read the state of the chips) and 1.8V power rail under the crystal in the third and fourth layers. Should this be a problem?

[LM21]

32kHZ are a bit tricky to use, but you have ground immediately below the crystal, if I understood you correctly. Then it does not matter what is below that ground. I think (but dot not know) crystal values, like load resistance, are more critical anyway (especially with 32k crystals..

[Benta]

I don't see any problem with that layout, 32 kHz is low frequency.
The major issue with the 32 kHz crystals is excessive drive power, it should normally be below 1 uW (yes, microwatt), which is the reason for the large series reistors you'll see in many oscillator designs.
But if the oscillator IC is already optimized for this, it's OK.

[Nikos A.]

Thank you guys!!

[Alex Eisenhut]

The only thing I'd bitch about is the lack of thermal relief on the crystal's load capacitors. 

[Nikos A.]

Thanks Alex,

Do you use to apply thermal reliefs to every component connected to a ground pour?

[tooki]

Well yeah, generally speaking, unless you need the maximum current capacity.