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Quadcopter PCB design tips

Posted: Tue Aug 28, 2018 11:24 am
by michprev
Hi,
I am designing PCB to be used on quadcopters. It should. include following:
  • ESP32-WROOM-32U (4 MB flash variant)
  • new ICM-20689 accel & gyro sensor
  • MS5611 barometer
  • external 128 Mbit SPI flash
  • JTAG connector
  • CP2102N USB-UART converter (24 or 28 pin variant)
Barometer and SPI flash will share VSPI bus. I will probably use 4 layer PCB. HW design guidelines paper says following:
  • 1st layer signal traces + components
  • 2nd layer GND plane
  • 3rd layer 3.3V plane + some signal traces
  • 4th layer power traces only
It is not recommended to place any components on bottom 4th layer.

Unfortunatelly I need to place barometer (and probably some other components due to size limitations) on the bottom layer. So I am thinking of using this scheme:
  • 1st layer traces + components
  • 2nd layer GND plane
  • 3rd layer 3.3V plane + few necessary signal traces
  • 4th layer traces + components
Is this ok? Is it ok to place components on the bottom layer under the ESP32 module with making sure that there is a complete GND plane under ESP32? Do you have any other suggestions?

Thank you!

Re: Quadcopter PCB design tips

Posted: Tue Aug 28, 2018 12:01 pm
by mikemoy
I am only using 2 layers and placed a PHY IC under it, with quite a few other parts. Works no problem. If your using 4 layers there should be no issue at all.

2018-08-28_6-59-01.jpg
2018-08-28_6-59-01.jpg (456.89 KiB) Viewed 2026 times

Re: Quadcopter PCB design tips

Posted: Tue Aug 28, 2018 3:20 pm
by michprev
Thank you for your answer. I have also seen that ESP32 DevKitC uses AMS1117 LDO regulator. I would like to use it as well. AMS1117 datasheet recommends to use 22 uF tantalum capacitors but DevKitC uses ceramic ones.

I would like to reduce noise on the power trace as much as possible. I have read that noise on the power trace can cause noise on the gyro data. I am thinking about adding one separate AMS1117 just for the gyro. What do you think about that?

Re: Quadcopter PCB design tips

Posted: Tue Aug 28, 2018 4:04 pm
by Deouss
  • 1st layer traces + components
  • 2nd layer GND plane
  • 3rd layer 3.3V plane + few necessary signal traces
  • 4th layer GND plane
  • 5th layer traces + components
Connect 2nd and 4th

Re: Quadcopter PCB design tips

Posted: Tue Aug 28, 2018 4:45 pm
by michprev
Deouss wrote:
  • 1st layer traces + components
  • 2nd layer GND plane
  • 3rd layer 3.3V plane + few necessary signal traces
  • 4th layer GND plane
  • 5th layer traces + components
Connect 2nd and 4th
5 layer PCBs are not standardly used :lol: and 6 layers are unnecessarily expensive

Re: Quadcopter PCB design tips

Posted: Tue Aug 28, 2018 5:05 pm
by Deouss
But you get perfect noise reduction for the price cost of course )