Re: [EE]: PCB layout of crystal oscillator for MCU

Hi Sean,

My board stack up are as following:

Top layer: Mostly signal traces, with ground pour to the entire board area.
2nd layer: Mostly ground pour, with some signal traces.
3rd layer: Ground pour entire area, with VDD (5V) fill zone to cover all
VDD vias, and a tiny 3.3V fill zone (about 1 - 2 cm square). 2 signal
traces  (UART Tx and Rx) are running through the ground pour, and one short
trace of very low speed digital signal is running through the Vdd zone.
Bottom layer: Ground pour (almost no signal trace, except a couple of parts
which cannot be placed on top layer)

The reason I want a void zone for VDD underneath the crystal area is to
avoid feeding high frequency signal into VDD. Do you think this NFZ is
unnecessary?

Many thanks.

WH Tan


On Fri, 21 Aug 2026 at 12:17, Sean Breheny <[email protected]> wrote:

> Overall it looks very good to me. What are the other layers in your
> stackup? Why do you want to prevent Vdd fill under the crystal?
>
> On Thu, Aug 20, 2026 at 11:00 AM WH <[email protected]> wrote:
>
> > Hi,
> >
> > This is my very first attempt to layout a crystal oscillator for MCU of
> > TQFP package. Attached screenshot shows the top layer of 4 layers stack
> up.
> > The MCU is PIC18F57Q84-I/PT and the crystal is
> ABM11W-16.0000MHZ-8-B1U-T3.
> > Link: ABM11W-16.0000MHZ-8-B1U-T3 Abracon LLC | Crystals | DigiKey
> > <
> >
> https://www.digikey.my/en/products/detail/abracon-llc/abm11w-16-0000mhz-8-b1u-t3/7172584
> > >
> >
> > Prior to coming up with the work as shown in attached screenshot, I have
> > read some application notes and suggestion on the webs but I still have
> > some doubts.
> >
> > 1) The stitching ground vias: should I bring them closer to the crystal?
> >
> > 2) The rectangle inside the stitching vias is construction lines I used
> to
> > define a no-fill-zone for VDD layer. Should I make it larger to cover the
> > stitching vias, or smaller to just cover the crystal, or leave it as
> shown
> > in the screenshot?
> >
> > Appreciate any advice and comments.
> > Thanks very much.
> >
> > --
> > WH Tan
> > --
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-- 
WH Tan
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