Touch pad for ESP32 ESP32-D0WD touch sensor

[Watth]

Hello EEVblog folks!
I am looking into making a touch pad for an ESP32-D0WD on a PCB.
From what I understand, a simple copper zone can do the trick. But I still have questions:
Are there dimensions restrictions (min or max)? Are there issues with ground plane on the opposite side?
Are external components needed?
Does the pad nee to be conductive, or not (for example covered by solder mask and/or silkscreen) ?
How does the touchpad influence/limit the pin's behavior as a GPIO (if not used as a touch sensor)?

Thanks for reading!

[PGPG]

I believe if some IC offers touch pad sensing than there have to be AppNote describing it in detail.

[Watth]

You are right, I should have explored this more.
FYI, I found this: https://docs.espressif.com/projects/esp-hardware-design-guidelines/en/latest/esp32/pcb-layout-design.html#touch-sensor

[xvr]

More info:

https://github.com/espressif/esp-iot-solution/blob/release/v1.0/documents/touch_pad_solution/touch_sensor_design_en.md
https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/cap_touch_sens.html

[Watth]

Hey xvr,
In the meantime, I found the first link you provided, I was about to update my latest reply!
As for the second link, it is about the software part, but I'll keep it in my bookmarks.