Quadcopter PCB design tips

[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!

[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 (456.89 KiB) Viewed 7630 times

[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?

[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

[michprev]

• 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 and 6 layers are unnecessarily expensive

[Deouss]

But you get perfect noise reduction for the price cost of course )