STM32L412 32.768kHz Crystal Layout Queries

[DBhut.1]

Hello,

We are facing RTC Drift as mentioned in previous question, So We have some queries regarding PCB Layout.

1) GND of Crystal's Capacitor is connected to nearest GND Pin of STM32L412, should I connect this MCU GND Pin to Common GND Plane?

2) How should we trace the Crystal Tracks? (below images are for reference)

a) - from Controller Pin to Crystal first (or)

b) - from Controller Pin to Oscillator's Load Capacitors first

because we have seen some reference where in which connections goes from

Controller pin to Capacitors first, and in some PCB Connection goes from Controller

Pin to Crystal first.

 

3) As shown in the Attached image, we have traced the Guard Ring around the Crystal Oscillator Components. In this

a) Please review layout

b) Vias should be Open masked or not?

 

Please give us support regarding this.

Thank You

[LCE]

Most important: GND! I still do not see a good connection between controller GND and board / crystal GND, or do you have inner layer GND plane now?

I see no reason in a "normal design" to leave openings in solder mask for vias, unless you want to use them as "dirty" testpoints or causes for short circuits. 😉

Check the crystals' datasheets, some like the GND directly underneath, some don't.

Capacitors and vias: for bulk capacitors for supply stabilization / filtering the connection is usually:

from GND / voltage via to capacitor, from capacitor to controller.

[DBhut.1]

GND of Crystal's Capacitor is connected to nearest GND Pin of STM32L412, should I connect this MCU GND Pin to Common GND Plane?

[AScha.3]

you need have a common ground area...look:

[DBhut.1]

Thanks for your efforts to make image for trace. But unfortunately, it is not possible to make due to other paths and vcc layouts.

So, conclusion is I can connect GND pin of MCU and Crystal Capacitor to common Ground plane.